Friday, December 31, 2010

12/31/10: Uncertainty With Longer Range

Note: The 5-Day Forecast page was not updated tonight, however the forecast remains the same with no changes.

In addition, instead of a long range update, an update for the winter outlook will be posted sometime over the next few days, which includes changes from the original forecast, especially for January.

--------------------------------------------------

Today's update will only be a brief one, as for the main part there are no changes from yesterday's forecasts, however there is increasing uncertainty for the medium and longer range starting on Tuesday.

Weekend Outlook:

The NAM and GFS models, which previously were too cold with the forecast highs for tomorrow due to the snow cover, are starting to correct their errors but are still too cold, showing high temperatures only in the mid to upper 30s. The GGEM continues to remain consistent with a warmer solution, and was used for the forecast. High temperatures tomorrow are expected to be in the lower to mid 40s inland, and in the mid to upper 40s for the rest of the area with a light SSW wind expected.

There are no changes from yesterday's outlook for the weekend, as the cold front is still expected to move through on Saturday night bringing light to occasionally moderate rain, with less than 1/4 inch of rain expected. Temperatures overnight will remain steady, if not slightly rise, and will peak on Sunday in the lower to mid 40s across the area with some upper 40s in the immediate NYC area. An isolated rain or snow shower is possible early on Sunday night, especially in the eastern parts of the area.

Next Week: Cold And Dry Pattern Returns, Uncertainty Returns

By Monday, we are looking at the return of colder temperatures as a cold and mainly dry pattern develops once again, similar in some ways to that of December. High temperatures on Monday will be in the upper 20s to mid 30s across the area, slightly rising on Tuesday. By Tuesday, however, uncertainty returns to the forecast as there are several storm potentials which the models are having difficulties handling.

The first potential is on Tuesday night into Wednesday, which some models show a clipper system bringing some light snow showers to the area with the storm intensifying further east. At this time, I am going with mostly cloudy skies with scattered snow showers, however this is a low confidence forecast and is subject to change.

By Friday and the weekend, there is another storm potential that according to some models may be a bigger one than Tuesday's potential. The GFS, GGEM and ECMWF models show a storm around that time frame, with the ECMWF showing the most extreme scenario with nearly 10 inches of snow for the area and the GGEM the least extreme with an offshore storm, but each model has significant differences when it comes to the development of the storm. It is too early to go into more details on this potential, however there is the potential for a storm to affect the area during this time frame. Stay tuned for more information on this potential storm over the next few days.

Thursday, December 30, 2010

12/30/10: Chilly And Dry New Year's Eve

The 5-Day Forecast was updated for the western and central parts of the area, with the forecast for Long Island/southern Connecticut to be updated late tomorrow morning. In addition, a long range update will be posted tomorrow in the "Long Range Forecasts" page about changes in the winter forecast.

-----------------------------------

Today was a mostly sunny day across the area with high temperatures generally in the upper 30s to lower 40s, however this morning's temperatures ended up busting too high as temperatures dropped to very cold lows inland, which the GFS and GGEM models hinted at last night but were too extreme with. These models had low temperatures in the single digits across the entire area and even below zero inland, and while it was not that cold, most locations in northwestern NJ and Orange County, NY saw lows in the mid to upper single digits, and Montgomery airport even reported a low of 3 degrees!

Temperatures will continue to slowly warm up over the next few days, peaking in the mid to potentially upper 40s on Saturday, but after a cold front brings some showers overnight, a cold and dry pattern will resume, with temperatures returning to slightly below average levels with no precipitation in sight until the second week of January.


Tomorrow's Outlook and New Year's Eve:

Tomorrow will be a partly sunny day across the area with a light SW wind expected. High temperatures will be in the lower to mid 40s across the area, with the warmest temperatures in the warmer spots in the immediate NYC area, such as Newark.

Unlike the last two years, when New Year's Eve brought wintry precipitation to the area, this year dry conditions are expected with partly cloudy skies for the start of the new year, with low temperatures chilly but not as cold as the last few days, only in the mid to upper 20s inland and in the upper 20s to lower 30s for the rest of the area. A very light SW wind is expected.


Saturday - Sunday: Mild, Cold Front Brings Some Rain

On Saturday, as a storm currently developing in the Plains will be entering Canada from Minnesota, it will bring its cold front through the Ohio Valley. The cold front will be at its strongest tomorrow, when it will bring severe weather from Missouri into Louisiana and unseasonably warm temperatures into those regions, even peaking in the 60s as far north as Illinois, but it will weaken by the time that it reaches the area.

The NAM and GFS continue to show high temperatures only in the lower to mid 30s, and as a result I used the GGEM again when making the forecast for this time frame, with high temperatures in the lower to mid 40s across the area on Saturday with a few upper 40s possible in the immediate NYC area in the warmer case scenario. Temperatures will drop a little overnight but will remain generally steady, with occasional showers expected but with light rainfall amounts less than 1/4 inch. On Sunday, showers will end in the morning with high temperatures peaking in the lower to mid 40s across the area.


Monday And Beyond: Cold, Dry Pattern To Start January

Behind the cold front, a colder air mass will return into the area, and low temperatures on Sunday night will drop into the upper 10s to mid 20s across the area. The wave of low pressure mentioned last night is less evident on the models, now nothing more than a few rain/snow showers, and the latest expectation is for an isolated rain or snow shower early with otherwise clearing skies.

Monday will be a colder day for the area with 850 mb temperatures below -10c again, with high temperatures expected to be in the upper 20s to mid 30s across the area. As the cold air mass will slightly weaken afterwards, temperatures will also slightly warm up, staying in the lower to upper 30s across the area.

There is no sign of any storm affecting the area until at least January 8-9, when the models are starting to show the potential for a storm. There are significant differences with each model and how it handles this potential storm, with the ECMWF showing a suppressed snowstorm and the GGEM model showing a coastal snowstorm. There is still a lot of time left until then, and there will not be a better idea of the potential scenarios this storm might take until it enters at least the hour 180 range, but there is the potential for the storm in this time frame. Stay tuned for more information on this time frame over the next few days.

Wednesday, December 29, 2010

12/29/10: Quiet Start To January

With partly sunny skies today, high temperatures were in the mid to upper 30s inland and in the upper 30s for the rest of the area, which was again slightly warmer than expected. Temperatures will continue to warm up over the next few days as the snow continues to melt, with the highest temperatures on Saturday in the mid 40s, however a chilly and dry pattern will set up again afterwards, with the only notable event during the first week of January being light rain/snow from a cold front on the 2nd.


Thursday - Saturday: Warming Up

Tomorrow will be another mild day for the area with mostly sunny skies expected. High temperatures will be in the mid to upper 30s inland and in the upper 30s for the rest of the area, with a few lower 40s possible in the immediate NYC area. A light west wind is expected.

Temperatures will continue to steadily warm up through Friday and Saturday as a much warmer air mass moves into the region. While the warmest air will stay to the west of the area, there will still be slightly warmer temperatures. The NAM and GFS model are most likely too cold in the area, apparently due to the snow cover that is in the region, showing high temperatures on Saturday only in the lower to mid 30s, however they also showed high temperatures in the lower to mid 30s for today when they were at least several degrees warmer.

As a result of the NAM/GFS cold bias, I am leaning towards the warmer GGEM model for the forecast temperatures, with upper 30s to lower 40s on Friday and lower to mid 40s across most of the area on Saturday. High temperatures on Saturday in the upper 40s may be possible in NYC in the warmer case scenario, however at this time I am keeping temperatures slightly lower. New Year's Eve will be mostly clear and chilly but warmer than the previous nights, with low temperatures in the mid 20s to lower 30s across the area.


Sunday - Monday: Cold Front, Light Rain and Potential Light Snow

The storm in the Midwest that will bring a blizzard there for New Year's Eve will bring a cold front through the Ohio Valley on Saturday, which will start to bring some light scattered showers to the area on Saturday night through Sunday. Temperatures on Saturday night will be steady in the mid 30s to lower 40s across the area, and depending on the timing of the cold front may drop by the late afternoon on Sunday.

On Sunday night, however, there is some uncertainty with a potential weak wave of low pressure that may develop along the cold front. The 12z GFS showed a wave of precipitation bringing light snow inland and light rain changing over to snow showers further east, with the 12z ECMWF also bringing light precipitation. While the GFS may have its progressive bias coming into play, this time frame will be kept an eye on for the potential of light rain/snow on Sunday night. If any precipitation does fall, however, it should be light, with light snow accumulations where snow does fall.


Afterwards, signs are that a chilly and dry pattern may develop again, with high temperatures returning into the upper 20s to mid 30s by Monday, slightly warming up by Tuesday. There does not appear to be a threat of any significant weather until at least January 7-10, when the models show the potential for a storm but with significant differences regarding the storm's development, track and timing. Stay tuned for more information on this time frame.

Tuesday, December 28, 2010

12/28/10: New Year's Eve/Day Outlook, Longer Range

Notes:

- The 5-Day Forecast was updated for the area except Long Island/S CT. A full update of the 5-day forecast will likely be posted tomorrow morning.

- The Storm Summary page was updated, with summaries for significant storms from late September through yesterday's blizzard.

- As many of you have observed, 2010 was an extreme year in weather in the NYC area and in the region, with four historic blizzards in one year, extreme heavy rain storms, strong wind events, several tornadoes in NYC, and extreme heat. As 2010 is coming to an end, I opened a poll about which event this year was the most extreme. Pleave vote your thoughts in the poll, which will close on January 5th.

----------------------------------------------

Today was a partly cloudy day across the area, with the winds starting to calm down after the strong wind gusts from the blizzard that continued through the day yesterday. Temperatures overnight failed to reach the forecast, and the high temperatures were slightly warmer than expected, however a milder pattern will set up for the next several days, with temperatures even returning into the 40s by Friday.


Tomorrow's Outlook:

Tomorrow will be a mostly sunny day across the area with a generally light west wind as a high pressure approaches the area. High temperatures will be in the lower to mid 30s inland and in the mid 30s for the rest of the area.

Low temperatures tomorrow night, however, will briefly get colder again with a high pressure in place along with mostly clear skies and light winds. There is some slight uncertainty with how cold it gets, with the GFS model the outlier showing temperatures in the single digits across most of the area, however low temperatures are likely to be in the 10s away from the coast.


Thursday And New Year's Eve: Slowly Warming Up

On Thursday, a storm near the Rockies will develop that will bring a New Year's Eve snowstorm to the Midwest, which that storm will start to draw in cold air into the western United States, with warmer air into the eastern United States. Even though 850 mb temperatures will be much warmer, some cold air will continue to be trapped over the area, preventing temperatures from rising well into the 50s as such an air mass would usually suggest.

High temperatures will only slowly climb through the week, reaching the mid to upper 30s across the area on Thursday, and in the mid 30s to lower 40s on Friday. New Year's Eve is expected to be mostly to partly clear with low temperatures in the mid to upper 20s inland and in the upper 20s to lower 30s for the immediate NYC area, which is warmer than the previous nights.


New Year's Day And Beyond: Quiet Pattern To Start January

On Saturday, the storm in the Midwest will start to bring a cold front through the Ohio Valley with rain and thunderstorms. Cold air will still be trapped over the area, and while the GFS model is most likely too cold with keeping high temperatures only in the lower to mid 30s, high temperatures will still not warm up to their full potential, only reaching the upper 30s to mid 40s. As the cold front comes through, it will weaken, bringing cloudy skies and occasional showers to the area on Saturday night into Sunday morning with temperatures steady in the 30s to lower 40s, dropping once the cold front clears the area.

Behind this cold front, a colder air mass will return into the area with high temperatures back into the upper 20s to mid 30s range for Monday, however this cold air mass will not be as strong or as sustained as those we have seen earlier this month, with the core of the cold in Canada. On Tuesday, the cold will weaken, and with no significant storm active near the region, this will lead to a quiet start to January, and at this time there does not appear to be a threat for any significant weather until at least the January 7-10 time frame.

Monday, December 27, 2010

12/27/10: Warmer Temperatures Return

Notes:

- The 5-Day Forecast was updated for the area except for Long Island/S CT.
- The poll for yesterday's storm ended on Friday night, with the results posted below:

7 votes - Storm well to south, dry and cold
2 votes - Storm clips NYC with light snow
18 votes - Intensifies near coast, heavy snow
1 vote - Too far north, rain/mix

-----------------------------------

The snow from the blizzard has ended this morning, but the strong winds from the storm continued to affect the area through the day, with widespread blowing snow observed. The skies have cleared with temperatures tonight dropping to some of the coldest this winter, but over the next week a warming trend will start that will lead to the warmest temperatures in the area since early December.


Tomorrow's Outlook:

Tomorrow will be a partly sunny day across the area with a breezy west to WNW wind expected. Winds will not be as strong as today, however gusts up to 40 mph are still possible near the coast. With the cold temperatures and the breezy conditions, wind chills will be in the single digits across most of the area in the morning, with sub-zero wind chills even possible northwest of NYC.

Temperatures will start to warm up a little as the cold air mass weakens, in the lower to mid 30s across most of the area, though a few upper 20s are possible in the higher elevations inland with some mid 30s in the immediate NYC area.


Wednesday - Friday: Warming Trend

By Wednesday, a storm will start to take shape in the Rockies, bringing behind it a much colder air mass into the western United States. Usually, a trough in the west coast means a ridge in the East Coast, and this case will be no different. By Thursday, 850 mb temperatures will warm up above 0c, the first time since December 13, but with a high pressure over the area, temperatures will not warm up as much as areas further west as some cold air gets trapped over the area. High temperatures will only be in the mid to upper 30s on Thursday, and while on Friday, temperatures will be slightly warmer, in the mid 30s to lower 40s, they will be significantly warmer to the west of the area, peaking in the 50s in Illinois.

New Year's Eve should be partly cloudy across the area with no precipitation expected. Low temperatures overnight will be much warmer than previous nights, in the mid to upper 20s inland, and in the upper 20s to lower 30s in the immediate NYC area.


New Year's Day And Beyond

With a storm tracking through the Midwest, bringing a snowstorm to those areas on New Year's eve, and the high pressure exiting to the east, temperatures will warm up even more, but will still be cold compared to areas further west, with high temperatures only in the upper 30s to mid 40s across the area. Further west, meanwhile, high temperatures will be in the lower 50s as far as West Virginia and possibly SW PA, and may even reach the 60-degree mark in southern Virginia.

On Saturday night into Sunday, the storm's cold front will approach, potentially bringing steadily warming temperatures overnight potentially peaking well into the 40s by Sunday morning, with a round of rain late Saturday night through Sunday. Behind this cold front, a much colder air mass will enter the region, with high temperatures potentially dropping into the upper 20s to mid 30s again for early next week, however this cold will not be as strong or as sustained as the cold we saw earlier this month.

Final Blizzard Of 2010 Summary

Last night into this morning, the NYC area was affected by one of its worst blizzards in recorded history. Heavy snow fell at rates of over 2-3 inches per hour, wind gust exceeded 50 mph and even peaked 68 mph in New London, CT and Bayville, NY, and snowfall amounts exceeded 20 inches in most of the immediate NYC area. What was almost as amazing as the storm itself, however, was the surprise as it came, as 2 days before the storm there were very little signs on the models that the storm would be anything even close to being what it was.

Forecasting The Storm:

Up to the day before the storm, it was very difficult to make a forecast for this storm, as the models had two separate solutions with no real consensus. The storm started showing up on the GFS model as a notable snowstorm for the area on Christmas day on December 17, which I did a section in that day's update focusing on the storm potential, and from the following day, a split in the model solutions began that lasted until a few days before the storm, with some models following an out to sea solution, bringing barely some snow to eastern Long Island and Cape Cod, while other models took the storm up the coast, bringing heavy snow to the area. At that time, there was evidence to support both solutions, but despite the majority of the models keeping the storm out to sea, the reliable ECMWF model was showing the blizzard solution consistently, being why I decided to go with a solution close to the ECMWF, showing the big snowstorm potential areas from Long Island into southern New England.

On Wednesday the 22nd, the storm's energy moved inland into the western United States, producing another round of heavy rain and snow to California, which was already hit with heavy rain and snow prior to this storm. Usually, once the storm's energy moves inland, it can be sampled better, and the models start to reach a consensus that usually lasts until the storm arrives. That consensus, however, was an out to sea solution, and even the ECMWF model that was consistent with a blizzard for the area having trended well to the east. The pattern up to that point supported an out to sea solution, and since this was in the short range, when the models typically start to reach a consensus, I also followed along with this trend. The models, however, still had some trouble handling the storm, which was the reason why I did not remove snow chances from the forecast in case it would trend west.

Between Friday afternoon and Saturday afternoon, however, a very unusual short range trend took place that put the area back in the big snowstorm potential. Up to that point, there was uncertainty whether the storm would move up the coast and intensify, or whether it would stay weak and well east of the area. On Friday afternoon, 2 days before the storm, a run of the GFS model came in that suddenly showed the storm moving up the coast, bringing a blizzard to the area. While this run was originally discarded due to apparent initialization errors, the 00z run of the NAM, which uses new data, also showed a much further west solution, the GFS trended even more west, and the UKMET also trended west. Such a big trend is very rare in the 48 hour range, which is when models would usually be consistent with the final solution. This last minute trend was mentioned as a possibility in the discussion on Friday, and became reality on Saturday when every model finally showed a big snowstorm, less than 36 hours before the storm started.

Storm Summary:

**The radar image below is from the peak of the storm, taken around 8:28 PM.**

The storm first affected parts of the Southeast into the Carolinas and Virginia on Saturday, bringing a rare white Christmas to these areas, however the storm did not start moving up the coast until Sunday morning, when it was off the coast of North Carolina and only starting to rapidly intensify. Snow started spreading into the area between 10-11 AM, and with temperatures only in the 20s, was able to start accumulating from the start. By 12 PM, a steady moderate snow was already falling in the central and eastern parts of the area with light accumulations up to at least an inch, and winds started to increase a little, but the worst was still to come.

By 2 PM, heavy snow bands already set up in central NJ and were starting to move into New York City and Connecticut. Winds were steadily increasing across the area with decreasing visibility, and the snow continued to become heavier in the western and central parts of the area. Around 4 PM, eastern Long Island was already starting to mix with sleet as precipitation became much lighter and a dry slot moved in, meanwhile the snow band that affected NYC was starting to set itself up in northeastern New Jersey, where it would stall for the rest of the evening and produce the heaviest snow amounts.

The worst of the storm started around 5 PM, when snow amounts were still light, only between 2 and 5 inches across most of the area. The heavy snow band set itself up in NE NJ, and wind gusts were already starting to increase, frequently gusting over 50 mph, and with temperatures only in the upper 10s to lower 20s away from the coast, wind chills were well into the single digits. The heavy snow and blowing snow created whiteout conditions, with near zero visibility for several hours, and snow rates were near 2 to 3 inches per hour. Thundersnow was even observed in the immediate NYC area. The eastern parts of the area started seeing heavy snow again as heavy snow bands moved in from the ocean, while the western parts of the area, being west of the heavy snow band, saw a steady moderate to locally heavy snow.

By the overnight hours, after 11 PM, the snow bands started weakening as the storm briefly stalled close to Long Island. As the worst of the storm moved into New England, the snow started weakening across the area, ending by the morning hours on Monday.


Storm's Aftermath:

**The map below shows estimated snowfall from the storm, which may be off in some places.**

While heavy snow amounts were widespread from North Carolina to Maine, the heaviest snow amounts from this storm ended up in New Jersey, with a report of 31 inches in Elizabeth, New Jersey. The heaviest snow amounts ended up in the immediate NYC area with widespread 20-30 inch amounts, with smaller amounts further west where there sharp cut off between the light and heavy snow was, leading to anywhere between 4 inches to as much as 20 inches in the western parts of the area. Long Island generally saw between 10 and 20 inches of snow, and southern Connecticut saw anywhere between 5 inches further east to as much as 18 inches further southwest. With 20 inches observed in Central Park, this was the 6th biggest snowstorm there on record.

While the storm verified for the area and even overperformed, the storm underperformed in some areas. Washington DC was expected to see between 3 and 6 inches of snow but as the map above shows, ended up with less than an inch. The storm's heavy snow axis ended up over the immediate NYC area as expected, but moved north northeast from there, not northeast, with lighter snow amounts than expected from eastern Connecticut into parts of Rhode Island and Massachusetts.

What made this storm different than some of the big snowstorms last year was that this storm was a true blizzard. While last year's snowstorms brought heavy snow and strong winds, none of them had these conditions as strong or as long lasting as this storm had, where many places observed wind gusts over 40 mph and near zero visibility for as much as 5-8 hours. The big snowstorm at the end of February last winter was mainly a wet snow event, which led to trees and roofs collapsing, while this storm produced powder snow, and the winds with this storm were so strong that they caused the snow to blow all over the place, reducing the risk of collapsing roofs and trees but created huge snow drifts.

Overall, this storm was one of the worst to affect the New York City area on record, and its surprise was just as bad as its impact, as it was not expected to be a major snow producer until the day before the storm. After a year of extreme weather events, ranging from the February blizzards to extreme rainstorms, hurricane force wind gusts, extreme heat waves and tornadoes in New York City, this blizzard is only an addition to a year of extremes that will be remembered for a long time.

Sunday, December 26, 2010

Dec 26, 2010 Blizzard Updates

Below, I will post brief updates throughout the day covering current observations, short term forecasts and any potential changes in the storm's forecast on the blizzard that will affect the area through Monday morning.


---------------------------------------------------


11:00 PM: The low pressure has significantly slowed down and is briefly stalling off the coast of Long Island, which will lead to heavy snowfall staying in the area for the next several hours. A very heavy snow band is moving into NE NJ right now, producing another round of 2-3"/hour snowfall rates. Temperatures are very cold, in the upper 10s to lower 20s across most of the area, which combined with wind gusts above 40 mph is leading to wind chills well into the single digits. An additional 4 to 8 inches of snow are possible tonight, with the heavy snow ending after 12-2 AM and light snow remaining until the morning hours.

The storm updates have ended for tonight. An update will be posted tomorrow morning reflecting the storm's forecasts, development, how it affected the area and the snow totals.


10:20 PM: The heaviest snow has ended for the area, however heavy snow is still ongoing and will not end until later tonight. Over the last 1-2 hours, places in the deformation band in northeastern New Jersey observed zero visibility, strong wind gusts near or even over 50 mph, and snowfall rates exceeding 2-3 inches per hour, with snow totals between 10-15 inches at this time. Waves of moderate to heavy snow bands took place in Long Island and S CT, with a steady light to moderate snow in NW NJ.

The low pressure is currently below 980 mb and is SE of Long Island, with very slow movement. The deformation band shifted slightly east and weakened a little, but is still capable of producing 2-3 inches per hour with strong wind gusts and zero visibility. Bands of moderate to heavy snow will continue to affect places east of this deformation band for the next several hours before starting to weaken after 12-2 AM, with an additional 4-8 inches of snow possible by the time that the storm ends. In NW NJ, light to moderate snow will continue and will slowly weaken over the next several hours.


8:40 PM: The worst of the blizzard is now taking place across the area, as widespread heavy snow is covering most of the area, visibility is near zero, wind gusts are near or over 50 mph, and wind chills are well into the single digits in some places. By the time that the storm is done, it will likely end up as one of the biggest snowstorms to affect NYC on record.

A heavy snow band with intensity between 35-40 dbz is stationary in western Bergen/eastern Passaic, eastern Morris, and the border between Rockland/Orange counties, which is producing very heavy snowfall with rates as high as 3 to 4 inches per hour, leading to these areas ending up with the biggest storm totals, likely between 18 and 24 inches of snow. Another heavy band is currently in Westchester county and in NYC, moving west while intensifying, producing rates of 2 to 3 inches per hour. With more bands of heavy snow forming offshore, heavy to occasionally moderate snow will continue falling across most of the area until late tonight, when the snow will start to weaken after 12-2 AM.


6:40 PM: Heavy snow bands continue to affect the NYC area at this time, and over the last 1/2 hour there were reports of thundersnow in the immediate NYC area, with even some cloud to ground strikes. The snow band's westward expansion was stopped around central NJ, so the western parts of the area will still see some heavy snow but with smaller amounts than the immediate NYC area. With temperatures in the lower to mid 20s across most of the area and strong wind gusts observed, with chills are very low, only in the single digits to lower 10s.

Widespread heavy snow bands are affecting Long Island and southern Connecticut, with these bands likely to reach the immediate NYC area around 8 PM after a small dry slot comes through briefly weakening the snow. Each snow band will be capable of producing snow rates between 2-4 inches per hour, strong wind gusts over 40 mph with blowing snow and near zero visibility, and more thundersnow can be expected.


5:30 PM: WARNING: A very heavy 35 dbz snow band is developing and expanding in western Long Island, near western Nassau county into eastern Queens, and is moving WNW to NW. This band will affect Queens and southern Westchester, and may extend into the rest of NYC and up to a line from Bergen county south into Staten Island if it does not weaken. This snow band is capable of producing strong wind gusts over 40 mph, snowfall rates up to 2-3 inches per hour, and thundersnow.


5:15 PM: The heavy snow band extending from Westchester county into NE NJ is producing near blizzard conditions, with heavy snow and strong winds. Snowfall accumulations are generally near or over 2-4 inches across most of the area, however will increase significantly tonight especially in the immediate NYC area as the worst of the storm is only starting.

Light to moderate snow continues to fall in NW NJ, with bands of moderate to heavy snow slowly moving in from the east. Developing snow bands offshore will bring moderate to heavy snow into most of Long Island where a dry slot brought much lighter snow mixing with some sleet, with the heaviest snow from western Long Island into NE New Jersey and SW Connecticut, where snowfall rates will increase up to 2-3" per hour at times, along with strong wind gusts and blizzard conditions.


4:00 PM: The heavy snow band is currently affecting northeastern New Jersey and SW CT, however it has weakened from earlier this afternoon, leading to lighter snow rates. While the snow is about to temporarily end in eastern Long Island as a dry slot comes through, bands of heavy snow are forming off the New Jersey coast as the low pressure, now near 988 mb and east of Delaware, continues to rapidly intensify while moving NNE up the coast, which is producing very heavy bands of snow in southern New Jersey and even some thundersnow.

Once the low pressure gets to New Jersey's latitude, these heavy snow bands will move north along with the storm, and will bring a much more widespread heavy snow focusing on the immediate NYC area, SW CT and western Long Island by this evening, and it is possible that as the storm slows down, they could also stall over the area for a while. These bands will be able to produce wind gusts of 40-50 mph or even higher, snow rates of 2 to 3 inches per hour, and thundersnow. Depending on where the heaviest snow bands end up, isolated areas could see amounts as high as 2 feet of snow.


2:35 PM: Over the last 3 hours, snow spread across the entire area and steadily intensified. A steady light to moderate snow is falling in the western parts of the area with a moderate, wind-blown snow across the rest of the area.

A heavy snow band is currently stretching from Cape May through central NJ into NYC and Long Island, and is slowly moving NW. This band is capable of producing heavy snowfall with rates up to 2-3 inches per hour possible and strong wind gusts over 40 mph. This band will continue to affect NYC while spreading into extreme SW CT, SE New York, and northeastern New Jersey. Heavy snow but not as heavy as the band in NYC will spread into NW NJ over the next several hours. Meanwhile, the snow will start to become lighter in Long Island.


12:00 PM: Light snow is already covering most of the area, with moderate snow falling from NYC and further east. Light accumulations are already being observed in places where snow is falling, as with low temperatures the snow can easily stick on most surfaces.

The snow is slowly expanding northwest, and around the next hour, light snow should start falling in the western parts of the area, but the heavier snow will not move in until later this afternoon. The snow may briefly weaken in the suburbs north and west of NYC in the short term, but between around 1-2 PM, potentially a little earlier or later, the heavier snow bands will start moving in from the south southeast. Long Island is seeing heavier snow moving in, and for the next several hours the snow will continue to gradually intensify.


10:45 AM: Light snow has started to fall across the eastern parts of the area, with some places reporting a dusting of snow already. The snow is expanding while moving NNE, and will continue to spread into southern Connecticut and steadily intensify over the next several hours with light accumulations expected. Further west, in the immediate NYC area, light snow will start to fall, but will not start to steadily intensify until after 12 PM. In the western parts of the area, light snow will only begin to fall after 12 PM, after the rest of the area starts to see snow. The snow will steadily intensify across the area through the early afternoon hours, with the heaviest snow until then in the eastern parts of the area.

We are currently seeing a 992 to 996 mb low pressure just off the coast of eastern North Carolina starting to become more negatively tilted. The latest NAM and GFS models are further east with the storm, bringing considerably smaller amounts to western New Jersey, however they are still having some issues, with the short term models further west with the storm. Updates through this afternoon will also focus on the location of the low pressure and whether it appears to follow the western or eastern solutions, though at this time observations seem to support a further west scenario, like the one described last night.

Saturday, December 25, 2010

12/25/10: Final Storm Forecast

Today was a mainly cloudy day across the area as the leftovers of a snowstorm in the Ohio Valley brought scattered snow showers to parts of the area today. Looking at the latest radar, light to moderate snow is currently falling in southern Virginia with more snow headed towards these areas. We are currently tracking a low pressure moving through Florida right now, which tonight into tomorrow will start to turn northeast and then north to bring a blizzard to parts of the area into southern New England that may rival some of the blizzards of last winter.


Storm Development And Track:

Up until today, the storm's development was the most uncertain part of the forecast, and put the range of possibilities from a major snowstorm to no snow with barely a small shift. Several days ago, it was mentioned that the two possible tracks would either take this storm up the coast or out to sea, but the models trended to a consensus that was out to sea once the storm's energy entered the United States. While usually, the models would then become more consistent with this solution as this was in the short range, the GFS model started an unusual last minute trend yesterday that was big enough to bring heavy snow well into the NYC area, and now it appears that the storm will take the western path up the coast.

Up until tomorrow morning, the radar appearance of the storm may make it seem as if it is going out to sea, when it will not do so. Tonight, as precipitation continues to affect Virginia and the Carolinas, the low pressure will move towards the coast of the Carolinas, with a NE movement making it seem as if the storm is going out to sea, however the storm will start to take more of a neutral tilt, meaning that it will start to move NNE and then north. Yesterday's model runs had the storm with a positive tilt when off the coast of the Carolinas, meaning it would continue to move northeast and out to sea, though now all of the models show a neutral to slightly negative tilt by that time.

By the early afternoon hours, as the storm starts to move more north while rapidly intensifying, the precipitation will start to move more north, extending slightly west the further north the storm gets. It is then expected to peak between 970 and 975 mb tomorrow night while briefly stalling off the coast of Long Island. Afterwards, the storm will start to move northeast and away from the area while producing windy conditions.


Forecast For The NYC Area:

Until at least tomorrow afternoon, cloudy skies with an isolated flurry are expected for the area as the storm develops to the south of the area. Starting around 12-2 PM, snow will move into the area from south to north, steadily intensifying and becoming heavy by the late afternoon hours. Temperatures will be stuck in the mid to upper 20s across most of the area, with upper 20s to lower 30s further east. By the late afternoon hours, as the storm slows down southeast of NYC, widespread heavy snow will start to cover the area, with increasing winds and dropping temperatures, leading to a high liquid to snow ratio snowfall across most of the area as snow will fall with temperatures in the lower to mid 20s away from the coast.

The heaviest snow will fall between the late afternoon and overnight hours, with the heaviest snowfall in the immediate NYC area and western/central Long Island and southern Connecticut. Due to the proximity of the storm, the snow may mix with rain at times in eastern Long Island, which will lead to slightly lower snow accumulations there. At the peak of the storm, snowfall rates as high as 2-3 inches per hour are possible where heavier snow bands develop, wind gusts potentially over 40 mph will lead to blizzard conditions at times for the central and eastern parts of the area, and even thundersnow cannot be ruled out. By the morning hours on Monday, the snow should start to come to an end as the storm exits the area.


Forecast For The Northeast Region And Snow Map:

By the time that the storm is over, between 8 and 16 inches of snow are possible inland, 12 to 18 inches for the immediate NYC area, and 10 to 18 inches for Long Island and southern Connecticut as potential mixing will lead to slightly lower amounts in eastern Long Island. Depending on where the heavier snow bands set up, amounts locally as high as 20-24 inches are possible in the central and eastern parts of the area, and while it is also possible that some places could see slightly lower snow totals than expected, snow totals will still be very high, over 10 inches in the immediate NYC area and western/central Long Island/S CT.

Due to the NNE/north motion of the storm at first, most of the heavy precipitation will stay offshore tomorrow afternoon, keeping snow totals lower in the Washington DC area, with up to 6 inches of snow possible there, but this will need to be watched as it is possible that the storm could end slightly west, bringing even more snow to DC. The storm's precipitation shield will then expand northwest, with heavy snow developing in the NYC area and moving northeast through much of southern New England into southern Maine.

It appears that there should be a tight snow gradient to the west and northwest of the storm, and there is some uncertainty on where this gradient sets up, which could be slightly west or east of the snow map above. Regardless of changes with this gradient, it will stay to the west of NYC, meaning that heavy snow is still expected in the central and eastern parts of the area, with the westernmost parts of the area having the potential for slightly lower snowfall amounts if this gradient is further east and the eastern parts of the area having the potential for rain mixing with the snow if this gradient is further west.

Even though the general storm scenario has been figured out, there can still be some slight changes while the storm is ongoing, including potentially shifting the heavy snow axis slightly west or east. Storm updates will be posted throughout the day tomorrow covering the short term forecasts and and any potential changes if needed.

This is a dangerous storm and has the capability of producing well over a foot of snow, blizzard conditions with near zero visibility at times, and very hazardous traveling conditions. Stay tuned for updates tomorrow on this storm.

12/25/10 Noon: Blizzard Warning For NYC

5:00 PM Brief Update: With the latest model guidance having trended even more west and even heavier with the precipitation, I extended the heavy snow warning inland and added a blizzard warning for the immediate NYC area and Long Island/S CT, with the latest expected amounts at 8-16 inches inland, 12 to 18 inches in the immediate NYC area and 10 to 18 inches in Long Island, where rain may mix with the snow in eastern Long Island. Locally higher amounts up to 22-24 inches are possible in the heavier snow bands.

A final storm discussion, covering the development of the storm, the forecast snow totals and timing for the area, and a snow map for the area will be posted late tonight, with storm updates being posted tomorrow.

12/25/10 Morning: Major Snowstorm Expected

Note: Snow and Heavy Snow watches have been issued. Please visit the "Weather Alerts" page for the latest alerts and potential snowfall amounts in each part of the area.

------------------------------------

Last night, the update mentioned that some models have trended west with the storm, and it was possible that if the overnight model runs trended west, this storm would be able to produce a significant snowstorm for the area with as much as over a foot in Long Island. The overnight and morning model runs have done so, and a major snowstorm as big as some of last winter's blizzards is now reality for the area.

Accordingly, I issued a snow watch inland and a heavy snow watch further east, which are likely to be upgraded to warnings later tonight. I went with snowfall amounts slightly lower than the models are showing, however some upward adjustments in snowfall amounts may be possible, especially in the central and western parts of the area.

As the storm moves north from the Carolinas and up the coast, it will rapidly intensify, stalling off the coast of Long Island on Sunday night before moving northeast by Monday. Starting Sunday in the early afternoon, the storm will bring widespread heavy snow to the area and windy conditions, and it is possible that a blizzard watch/warning may be issued for the eastern and central parts of the area. By the time that the storm is over, at least 4 to 8 inches, or up to 10 inches in the snowier scenario, are possible inland, with 8 to 14 inches in the immediate NYC area and 10 to 18 inches in Long Island and southern Connecticut. Locally higher amounts up to as much as 20-22 inches may be possible.

There is still some uncertainty though as the models have not finished trending yet, and some slight changes are possible. Stay tuned for more updates on this storm tonight and tomorrow, as well as a final snow map.

Friday, December 24, 2010

Dec 24: Potential Snowstorm Update

Note: The 5-Day Forecast was updated through Monday only. A full 5-Day Forecast will be posted tomorrow.

As mentioned below, due to new uncertainty with the storm, a special update will be issued late tomorrow morning, and it is possible that snow and heavy snow watches may be issued depending on tonight's model runs.

----------------------------------------

Today was a mainly sunny day across the area with slightly cooler temperatures as the storm that was stuck over the Northeast for the last several days began moving out, bringing more sunshine and less windy conditions. Temperatures tomorrow will be again chilly, similar to today's temperatures, however cloud cover will be increasing ahead of this storm. Up until now there was a lot of uncertainty with this storm, and there is still uncertainty, however some models are trending towards a solution that might perhaps bring the potential of widespread heavy snow as far west as New Jersey.


Sunday - Monday Storm: New Trend May Change Forecast

Yesterday's models were consistent with the more east solutions that we observed with Wednesday and Thursday's model runs, and the discussion removed snow chances a little as there was increasing consistency in an out to sea solution. As briefly mentioned above, however, some of these models have started a trend which may put the NYC area in the potential for heavy snow. While it is too early to determine whether this is a real trend or just an error, this potential needs to be watched as more models continue to catch onto this possibility.


Model Analysis: The main model that started forecasting this storm as a blizzard, the ECMWF, remains out to sea with today's runs, as well as the GGEM and the UKMET. The GGEM model trended west in its 12z run today, but remains out to sea. The main highlight of today's models, however, were the GFS and NAM models, which trended west today to bring several inches of snow to the area.

The 12z GFS suddenly trended well west of its 06z run, producing over a foot of snow near and east of New York City. The 18z run went even more west, with over a foot of snow in NYC, northeastern New Jersey, Long Island and Connecticut. The NAM model also trended west with today's runs, with its 18z run bringing several inches of snow to the eastern parts of the area. While it was first determined that there were some errors with the way how the GFS and NAM initialized leading to these solutions, the 00z NAM, which uses new data, came in even more west of its 12z run, with snowfall amounts potentially between 7 and 9 inches in NYC and over 10 inches for Long Island and Connecticut.

While this may be an error, it is still too early to determine anything out of this potential trend. The 00z model runs, especially the ECMWF and GGEM will be important to see if they trend west, as well as the 00z/06z GFS to see if it remains consistent with its solution and if the NAM continues to trend west. If at least most of the above happens, this will confirm that this is most likely a trend. If not, we will have to continue following the models and making observations with the storm compared to the forecasts to determine which solution may happen. A special update will be issued late tomorrow morning about tonight's runs.


Forecast Set Up: Up until at least Sunday, the storm track is generally consistent with the models, however as soon as Saturday there are already differences with the models. The main difference comes with the phasing of the storm and how quickly it intensifies and starts to become neutrally/negatively tilted. Once the storm becomes neutrally tilted, it will start to move more NNE then north instead of going out to sea, but the question is where this happens. The latest GFS and NAM runs trended earlier with this, showing the storm already with a neutral tilt when near the Carolinas, while the further east models still have a positive tilt, meaning that the storm will continue to move NE and out to sea from that point. That is an important thing to follow with the model runs tonight and tomorrow, as the earlier the storm phases and shows a neutral/negative tilt, the further west it will be.


Thoughts For NYC Area: This was a very difficult forecast to make, and it may not be until the day of the storm itself that we know exactly what happens. Taking into account the western model solutions as well as the eastern models, I made very little changes to the forecast from 2 days ago, with a 40% chance of snow inland, 50% chance of snow for the immediate NYC area, and a 70% chance of snow for Long Island/S CT, which may be raised tomorrow depending on the model trends. It should be noted, however, that even if the storm misses the area well to the east, an upper level low will still bring scattered snow showers, so whether the main storm hits the area or not, at least some snow is likely to fall in at least parts of the area in the easternmost scenario.

As previously mentioned, tonight's model runs will be very important when trying to determine whether the western model runs tonight were off runs or if this is in fact a new trend. I will make a special update for this late tomorrow morning, and changes to the forecast may be made. If the main models remain east, there will not be many changes to the forecast. If, however, the GFS model remains west and the other models trend west, snow probabilities will be increased for the area, and snow and heavy snow watches may be issued for the appropriate parts of the area. There will also be the potential for up to or even over a foot of snow to fall in the eastern parts of the area if this solution is to verify. Stay tuned for more information on this storm and how it may affect the area.


Longer Range Update: Mild And Wet Start To New Year

As mentioned yesterday, the cold pattern will temporarily fall apart once the storm ends. Temperatures next week will be steadily warming up, meanwhile by the last day of the year, a significant storm will be taking shape near the Rockies, which will lead to a much warmer air mass spreading across the eastern and central United States. There is uncertainty with the exact track as this is in the longer range, but this storm will lead to mild temperatures for New Year's Eve and New Year's Day, with the storm's cold front then making temperatures briefly even warmer followed by rain. After the storm ends, the latest models show the potential of a cold pattern returning again, and this potential will be watched.

Thursday, December 23, 2010

Dec 23: Snow Or No Snow?

Today was a mainly cloudy day across the area as some snow showers from a storm affecting New England reached the eastern parts of the area and brought some reports of light accumulations there. Temperatures were generally in the lower to upper 30s across the area with windy conditions observed. Temperatures over the next several days will slowly cool down ahead of a potential storm on Sunday.


Sunday-Monday Storm Discussion: Snow Looking Less Likely

Over the last few days, today's model runs were mentioned as important runs as once the energy came onshore, the models would be able to sample it better and give us a better idea of where the storm could track. Today's models did start to agree on a general track area, which is leaning towards the out to sea scenario rather than the western scenario that would have brought a large snowstorm to the coast, but what especially helped lower snow chances was the ECMWF model that was the most consistent over the last few days with a big snowstorm, which went much further east today - barely bringing any snow to NYC when its runs yesterday had well over a foot of snow.


Model Analysis: As mentioned previously, the models started agreeing on a general track area today. The most noticeable trend came from the ECMWF, which is rather surprising as up until today it was the most consistent model, showing a slow and further west storm bringing a large blizzard to the Interstate 95 corridor. Its 00z (night) run was only slightly east of yesterday's 12z (afternoon) run, but today's 12z run had a huge east shift, keeping most of the snow offshore. While its next 2 runs will help determine if this was an off run or not, the fact that most of the models are also this far east makes it more likely that this could be a trend towards the general consensus, not an off run.

The GFS model, which trended west yesterday, is now one of the westernmost solutions, with its 18z run showing nearly 2-4 inches of snow in the immediate NYC area. Its morning 06z run though was even more west, with slightly higher snow amounts in NYC and over 10 inches of snow in far eastern Long Island. The GFS, however, is still not very consistent with the exact storm track, which is shown by its 12z run which was out to sea. The GGEM and UKMET models are still showing a solution that is out to sea, with the GGEM even further east than yesterday.


Forecast Track: There are still no major changes with the forecast scenarios from yesterday, however the eastern track that was shown on the map two days ago now appears to be more likely over the western track. The timing remains the same as yesterday, with this being a Sunday to Monday storm. The exact track mainly depends on the storm's timing and phasing, which we will likely have a better idea on over the next day or two.


Thoughts For NYC Area: The latest models today, as previously mentioned, trended away from a big snowstorm, especially the most reliable model, the ECMWF, and with the new consensus further east, I decided to lower snow chances for the area. Even though the 5-Day Forecast was not updated, I am currently putting the western parts of the area with a 30% chance of snow, the immediate NYC Area with a 40% chance, and Long Island/S CT with a 50% chance as there could be several inches of snow in Long Island/S CT if the western tracks verify. These percentages are still not final and are subject to change.

For the scenario map above, I used a scenario similar to that of the ECMWF and the GFS models, which are the western solutions at this time, to show that eastern Long Island and eastern New England have the best chance of accumulating snowfall from this storm if the western solution verifies. If they trend west from there, several inches of snow may extend into the area in the light blue, and while this is unlikely at this time, this potential will be watched as the models are still uncertain with the smaller details such as precipitation coverage area and intensity. It is still very possible, however, that the storm ends up going well out to sea and missing the area, which in that case, the area would only see scattered snow showers. At this time, my probabilities are based on a solution in between the eastern and the western solutions, which would favor at least some light snow in the eastern parts of the area, but this is subject to change based on tomorrow's model runs.

It is important to note, however, that the models are still having difficulty handling the storm's energy and the phasing and timing of the storm, with the models not too consistent with the exact track, especially the GFS. While there is a better idea on the general track area, it is possible that the storm could trend east and completely miss the area, just as much as it could trend west and bring the potential of up to several inches of snow in NYC like the GFS model is showing. Stay tuned for more information on this storm over the next few days.


Longer Range: Cold Pattern Temporarily Breaks Down

After this storm, one thing that is likely is that the cold pattern will break down throughout the week. Temperatures will be steadily warming up as the cold air mass weakens quickly, and by the late week there is the potential for another storm to form, however the models show that storm in the north central US, going along with the idea that the cold pattern temporarily falls apart. With this scenario, we are looking at a storm that could end up well northwest of the area, with warmer temperatures to start the new year and a potential storm for the first several days of the new year that may produce precipitation in the form of rain for the area. Stay tuned for more details on this time frame.

Wednesday, December 22, 2010

Dec 22, 2010: Sunday-Monday Snowstorm Potential

- The 5-day forecast was updated for the area tonight except for Long Island/S CT.

---------------------------------------------

Today was a mostly sunny day for the area with mild temperatures once again. With the storm in New England still bringing precipitation in these areas, cloud cover will likely increase tomorrow, but will decrease again for Friday. Temperatures will remain steady in the mid 30s to lower 40s through Friday, however by Saturday as a cold air mass pushes into the region, temperatures will slightly cool down. While a white Christmas is not expected, there is the potential for snow to fall in the area on the day afterwards.


Discussion On Storm: Snow Probabilities Slightly Increasing
Today, the models have reached a slightly better agreement with the general track area than yesterday, however there is still not a lot of agreement with the models. The ECMWF remains consistent with a historic snowstorm for the Interstate 95 corridor including the NYC area, while the GFS model, yesterday's eastern solution, has trended west today. While there is still a lot of uncertainty on which solution plays out an exactly how, at this time it appears that snow probabilities are increasing for the area.


Model Analysis: Yesterday's ECMWF models were consistent with showing a storm nearly hugging the coast, stalling off the Mid Atlantic coast and producing a historic blizzard for the region, with nearly 15-20 inches of snow and strong winds according to that model. Today's ECMWF runs were still very consistent with this solution with the only change being trending slightly slower with the timing. Considering the other models have also trended slower, I went with a slower timing for this storm, meaning that if any snow falls, it would start around Sunday evening and last through Monday evening/night.

The UKMET model trended east with its 00z run, as well as the GGEM, but came back further west in its 12z run. The GGEM stayed consistent with its 12z run, however given the time range this is in, the GGEM will likely change again tomorrow. The GFS model, which yesterday was the easternmost solution, was mentioned as a potential outlier, and came back further west today, bringing over 5 inches of snow to Long Island and up to an inch near NYC, which is a significant improvement over its runs last night and this morning. The GFS also trended much slower, making its timing more similar to that of the ECMWF, making it a more reasonable scenario.

There is still a spread with the models at this time, however with the storm's energy already onshore, the models will be able to sample it better, and tomorrow's runs will be very important when trying to determine the potential of this being a snowstorm for the area or not.


Storm Scenario: Up to at least Saturday, there are no major changes with the storm scenario other than slightly slower timing, potentially putting the storm in the extreme northern Gulf of Mexico or near southern Louisiana on Saturday. Up to that point, the models have become more consistent, however afterwards there is still a split with the solutions. The scenarios remain similar to those shown in the map yesterday, with one solution taking the storm out to sea and the other one bringing a big snowstorm to the coastal areas and the Interstate 95 corridor. The models today trended towards the ECMWF, which is still consistent with the western track, however the eastern track cannot be ruled out yet.


Forecast For NYC Area: After seeing today's models, with the majority of them bringing at least some precipitation to the area, I decided it was safe enough to upgrade snow chances to at least 50% inland, 60% for the immediate NYC area, and while I did not update the 5-Day Forecast for Long Island/S CT, I would put a 70% chance of snow in these areas at this time. Note that these probabilties are subject to change. It is still too early to go into snow amounts at this time, however depending on the model trends a preliminary snow map could be issued either tomorrow or Friday.

Due to changes in the timing, if it does snow, the snow would last from around Sunday evening through Monday evening/night. At this time, I am still conservative with the forecast, mentioning possible snow in the 5-Day Forecast, but as I mentioned earlier, with the energy now inland in the western US, tomorrow's models will be important in deciding this storm's snow potential. If the main consensus tomorrow is close to the ECMWF with more model support and consistency, this would give a higher confidence level for at least several inches of snow, if not even more. If the main consensus tomorrow is east, however, that would lower the snow potential. While we will not know for sure what happens tomorrow, there will likely be a better idea of the potential scenario that may verify.

While there is uncertainty on this storm at this time, this storm needs to be kept an eye on, as impacts could range from as little as no snow in the area to as much as over a foot of snow and strong wind gusts. Stay tuned for more information on this storm over the next few days.

Tuesday, December 21, 2010

Dec 21: Discussion On Dec 25-27 Storm

Today was a mostly sunny and breezy day for the area, with high temperatures in the mid 30s to lower 40s across the area, which once again was warmer than expected. Tomorrow appears to be another mild day across the area as high temperatures will be similar to, if not warmer than today, in the mid to upper 30s inland and in the upper 30s to lower 40s for the rest of the area. These temperatures will continue through at least Saturday, with dry conditions until then, however by Sunday a storm is expected to reach the region and may affect the area with snow and wind.


December 25-27 Storm Discussion: Split Continues Between Big Snowstorm Or Nothing

When making yesterday's discussion for this storm, the majority of the models took the storm out to sea, and even though the pattern so far this month would favor that solution, I did mention that there were some factors that make this snow event potentially more likely to verify than the previous potentials which ended up being too far south/east. Today's models trended more west again, and also trended slower, meaning that the snow will not fall on Christmas, but on the day after Christmas. While there are still at least 5 days left until the storm begins, there is enough confidence for higher snow probabilities in the area. There is still a split between the models about the storm's track, which still gives us a range of either a big snowstorm or a suppressed storm to the south/east of the area.


Model Analysis: The ECMWF model, which was the most consistent with showing the big snowstorm potential, continues to show the big storm with today's runs, and even shows a powerful 966 mb low pressure sitting east of New Jersey in its 12z run. The ECMWF, however, seems to be too slow with the storm, not showing the storm starting until at least Sunday night. At this time, this solution is a slow outlier, and the track is also potentially too far west, as no other reliable model shows the storm just east of New Jersey. The 00z ECMWF run was also potentially a little too strong and too far west, however it is more reasonable than today's 12z run and was used for the forecast.

The GGEM model has trended towards the ECMWF today, with its 00z run showing a big snowstorm for the area with apparently over 10 inches for NYC, but the storm would be so far west that rain/sleet mixing with the snow becomes an issue for Long Island. At this time, the storm is unlikely to be west enough to lead to precipitation other than snow falling in the area, and the 12z GGEM, which is slightly further east, is a more reasonable solution and was also used for today's forecast. The GFS model has trended much more suppressed, however it is currently the least consistent of the models, and is still slowly trending slower, meaning that it is still trending and could return further north/west tomorrow. At this time, I am considering the 18z GFS run as a potential outlier, but if the GFS is consistent with this solution tomorrow and/or other models trend towards it, then it could be a sign that the storm could be suppressed.


Storm Scenario: The models are generally consistent with the storm track until at least Saturday, when the storm is likely to end up near south Carolina, but from there where it goes is uncertain and depends on the phasing of the storm.

It is possible that the storm starts to intensify early and comes up the coast like the ECMWF and GGEM models show, which is the track to the left in the image to the left. This tpye of track would support a major snowstorm from the Delmarva Peninsula into New York City/Long Island and much of New England. The second possibility is the one that the GFS model is showing, where the storm doesn't intensify until it's too late, and as a result ends up moving ENE to NE and out to sea, keeping any snow away from the region. At this time, the more reliable models show the western track and the less reliable models show the eastern track.

Looking at the set up, it is more favorable than it has been for the potential December 19-20 storm which ended up being too far east, including a more defined western ridge and a sharper East Coast trough, which gives the storm a better chance to intensify and move up the coast. With the above mentioned, I am currently going for a solution in between, leaning towards the first track, but keeping the second track in mind as it cannot be ruled out yet.


Potential Scenario In NYC Area: At this time, as previously mentioned, I am thinking that a solution in between the first and second track, leaning towards the first track, may be more reasonable at this time. If I was to follow this scenario, there would be the potential of significant snowfall in the eastern parts of the area, with lighter snowfall west of NYC.

At this time, though, due to this being 5 days away and with uncertainty on the models, I am going more conservative with this storm, and while the 5-Day Forecast was not updated tonight, it appears that the best time frame for snow to fall would be on Sunday night, with at least a 40-50% chance for the western parts of the area, 50-60% chance of snow for the immediate NYC area, and a 60-70% chance of snow for the eastern parts of the area. It is still possible that it does not snow in the area, however if tomorrow and on Thursday the GGEM/ECMWF models stay consistent and the other models, including the GFS and UKMET, start to trend west, then I will probably increase the precipitation chances. On the other hand, if the GFS remains consistent and the GGEM/ECMWF trend further east, probabilities could be decreased tomorrow.

The scenario mentioned above is just a possibility at this time, and it is possible that other solutions might verify. If the eastern solution verifies, the area would likely stay dry, but if the western scenario verifies, as much as a foot of snow, if not even more could be possible in the central and eastern parts of the area. Both of these solutions are currently extremes, and at this time they remain only possibilities.

There is still uncertainty with the storm, and the scenario mentioned above is subject to change with future updates. Stay tuned for more details on this storm and how it may affect the area.

Monday, December 20, 2010

Dec 20: Christmas Storm, Too Far South?

Notes:

- The 5-Day Forecast was updated tonight.

- The poll for the Christmas storm impact on the area remains open until Thursday. So far, the majority of 7 votes is for heavy snow in NYC, with one vote for no snow in NYC, however it is not too late to vote yet!

----------------------------------------

Today was a mostly sunny day across the area with high temperatures in the mid to upper 30s across most of the area, which was slightly warmer than expected. The storm that was just offshore yesterday ended up bringing a big snowstorm to Cape Cod today, which was not predicted very well by some of the models, as 2 nights ago, some models didn't even have more than a few flakes there. This storm is expected to stick around for a few days, affecting the Northeast with snow showers and bringing increased cloud cover to the area, and while the cloud cover will briefly clear afterwards, the attention then focuses to a storm in the western US, which may affect the area on December 25-26.


Tomorrow's Outlook:


**Map correction: The 35 degree line should be moved slightly more NW on the map.**

Tomorrow will be a partly sunny day across the area with increasing cloud cover by the late afternoon and a NW wind expected, with breezy conditions along the coast. High temperatures will be in the lower to mid 30s inland, in the mid to upper 30s in the immediate NYC area, and in the mid to upper 30s in Long Island and southern Connecticut.


Wednesday - Friday: Dry, Slightly Warmer

By Wednesday, the cold air mass over the area will weaken, leading to warmer temperatures returning to the area. As snow showers take place to the north and east of the area, related to the storm that passed east of the area yesterday, high temperatures will warm up into the mid to upper 30s across most of the area, with some lower 40s possible in the immediate NYC area and in Long Island.

For Thursday and Friday, as the storm's influence starts to decrease across the region, the cloud cover will clear with mostly sunny skies expected, however temperatures will remain milder than they have been recently, with temperatures very similar to, if not slightly cooler than those of Wednesday. By late Friday night, however, cloud cover will start to increase again due to a storm approaching from the west.


Christmas Storm: Big Snowstorm Or Too Far South?

Yesterday, it was mentioned in the discussion that the models had 3 separate solutions for this time frame, the first and the least likely one being the western solution bringing a wintry mix to the area, the second scenario bringing a big snowstorm to the Interstate 95 corridor including New York City, and the third track taking the storm well south of the area, keeping the snow in the central and southern Mid Atlantic, or from Washington DC and further south. The western solution is no longer appearing on the models, signalizing that it was likely an outlier solution, however the split is now between whether the storm can make it far north enough to bring a big snowstorm to the area, or if it will stay south enough that the area stays dry.


Latest Model Summary: The models today are still not very consistent, considering this is still in the medium range, however there are now solutions that the models are split between. The ECMWF and the GFS models continue to show a big snowstorm for the area, however there are some differences between the two models, as the ECMWF digs the storm well south, into the extreme northern Gulf of Mexico, before being pulled NNE along the coast and bringing a large coastal snowstorm. The GFS model has the storm moving west to east through the central US like showed in yesterday's map, however with most of the models showing a further south solution, it is likely that the storm will start at least slightly further south than yesterday's map showed it.

Looking at the other scenario, the UKMET and the GGEM models support a storm that goes out to sea. The storm also starts out in the far southern US like the ECMWF model shows, but from there they take the storm out to sea, with intensification taking place too late that by the time that the storm starts to move northeast, it's already away from land.

Both of these solutions are reasonable at this time, and based on the pattern we've seen so far this month, the southern scenario would seem to be more likely, however there are some differences from the previous storm that give this storm a better potential to produce snow for the area. There is a more defined ridge in the western United States and a deeper trough in the East than the previous storm, which is usually better for a storm to move northeast and up the coast instead of simply going out to sea. The models are also more consistent than they have been at any point with the previous storm with a big storm close enough to the coast to produce a big snowstorm near or east of the I-95 corridor, and with the storm's energy moving into California in 2 days, the models will likely start to reach a better agreement by then.


Current Thoughts For Area: As mentioned previously, based on the pattern we've seen so far this month I'd prefer to go with the suppressed storm solution and keep the snow to the south of the NYC area, however there is also evidence suggesting that the set up is better than it was so far this month. At this time, I am going in between, slightly learning towards the suppressed solution, with at least a 40-50% chance of snow for NYC out of this storm, however this is still subject to change over the next few days, and may increase if more models start showing the northern/western scenario. In addition, the latest models have delayed the timing of this storm so that it starts on Saturday night and lasts into Sunday, and considering that the models that usually have a fast bias also trended slower to show this solution, it appears that if any snow falls in the area, it should start to fall around Saturday evening, and in the 5-Day Forecast, at this time I went with mostly cloudy skies and a chance of snow showers west of NYC for Saturday.

There is still uncertainty with this storm, and the forecast above could change. Stay tuned for more information on this storm over the next few days.


Longer Range: Cold Returns

Regardless of the path that the storm takes, the latest models show another round of cold air dropping down into the region behind the storm for early next week. As this is in the longer range, there is uncertainty on how cold it gets, though the latest model runs have been suggesting high temperatures potentially returning into the 20s again for parts of, if not most of the area. Windy conditions are also possible along with the cold due to the storm offshore, resulting in cold wind chills if this scenario verifies. Stay tuned for more information on this time frame.

Sunday, December 19, 2010

Dec 19: Christmas Storm Potential

Reminder: The poll for the scenarios for the storm on December 24-26 remains open. Please vote your thoughts in the poll, which will close on Thursday.

The 5-Day Forecast was not updated tonight, but the forecast remains the same through Thursday.

---------------------------------------

Today was a mainly cloudy day across the area as a coastal storm that yesterday affected the Southeast stayed mainly offshore, but brought some light snow to parts of eastern Long Island. The storm is now moving into southeastern New England, bringing rain and snow to Cape Cod. Several days ago, the models showed the potential of this producing a snowstorm for the area, however there were several problems with this potential, which led to the storm being too far east for any snow to fall in NYC.

This coming week will bring generally steady temperatures in the 30s, with a few lower 40s on Wednesday, however another storm will then affect the region on Saturday, which needs to be kept an eye on as it may affect the area.


Tomorrow's Outlook:

Tomorrow will bring clearing skies to the area with a breezy NW to NNW wind. High temperatures will be in the upper 20s to lower 30s inland, lower to mid 30s in the immediate NYC area, and in the mid to upper 30s for Long Island and southern Connecticut. A few readings above 35 degrees are possible in the warmer parts of the NYC area.



Tuesday - Thursday: Warming Up A Little

On Tuesday, the storm will continue to stay in the western Atlantic, meanwhile a weak low pressure will move ESE from the Midwest into the Great Lakes and towards the Mid Atlantic region, producing moderate to heavy snowfall into the Great Lakes. The clipper, however, will be unable to easily make it east of the Appalachians, and as a result the precipitation will significantly weaken, with only scattered rain showers making it east of the Appalachians as what's left of the storm becomes absorbed into the larger storm offshore. As a result, scattered rain and snow showers are expected in the central Mid Atlantic, in places such as Washington DC, with perhaps some rain/snow showers affecting the area.

The cold air mass will temporarily weaken on Tuesday before another cold air mass will enter the region by Thursday, leading to slightly warmer temperatures, potentially reaching the lower 40s in the warmer spots in NYC and the eastern parts of the area on Wednesday. In terms of precipitation, I went with mostly cloudy skies with an isolated drizzle or flurry possible in the 5-day forecast, as any precipitation should be isolated and light. Note that the 5-day forecast was not updated tonight, but the forecast hasn't changed for this time frame.

Thursday will bring colder temperatures to the area once again as another cold air mass returns into the region, but the attention then turns to the western United States, where a piece of energy entering California on Wednesday will start to move west to east through the United States, heading towards the area.


Friday - Sunday: Christmas Storm Potential - Mix, Snow Or Nothing?

Over the last 2 days, the potential for a storm to affect the area on Christmas Day has been mentioned as the models started showing a nor'easter affecting the area with near or over a foot of snow, especially on the GFS model. The ECMWF model has caught on to the GFS today, and while it was further east with the snow than the GFS, the exact precipitation area doesn't matter considering this is almost a week out, and the model spread is unusually small with greater than normal consistency considering this is in the hour 144-168 range. There are still some models showing other solutions, such as the GGEM keeping snow to the south of NYC, and the 18z GFS is further west of the storm, bringing rain and some snow to the area, but normally in this time range there would be a bigger range.

At this time, the models are generally in agreement with showing a piece of energy moving into California on Wednesday, which will bring another round of heavy rain/snow there before a break in the precipitation takes place for 2-3 days. By Thursday, the storm should be located near Arkansas/Missouri, however where it goes from there is a question. It is possible that the storm intensifies early and moves NE further west, leading to the 3rd scenario shown above and rain/mix for the area. The central solution, the one that the ECM/GFS are favoring, would bring a large snowstorm, if not a blizzard to parts of the area, and the southern solution, supported by the NOGAPS/GGEM/UKMET models would keep snow to the south of the area.

At this time, the western solution is not too likely, and it seems to be either that the storm brings snow to the area or it's too far south/east, but there is still time left until the storm's energy moves inland, which is when the models will likely start to get a better idea of the scenario. Stay tuned for more details on this storm and how it may affect the area.

Dec 19 Storm Updates

11:55 AM: As mentioned yesterday, the storm appeared further west on the short range models, giving a chance of accumulating snow in Long Island/S CT. The 00z NAM model run was the most extreme, showing nearly 2-4 inches for eastern Long Island, and while this was too much, there is still the potential of accumulating snow in eastern Long Island today, potentially up to 1-2 inches if the snow is heavy enough.

Looking at the radar, we are seeing precipitation off the coast moving northeast and intensifying while also expanding. While they may be too far east for NYC to get any snow, Long Island will likely see snow today, potentially mixing with rain near the immediate coast, with the best chance of snow, potentially accumulating, in eastern Long Island and SE Connecticut.


More updates on this will be posted later today, as well as an update tonight focusing on a potential storm that may affect the area on Christmas Day.

Saturday, December 18, 2010

Dec 18: Looking At Week Ahead

Notes:

- The 5-Day Forecast was updated for the entire area, the forecast temperatures for each part of the area can be found in the 5-day forecast. Tonight's discussion mainly focuses on the scenarios for the storms and less on the temperatures.

- The poll for tomorrow's storm has ended yesterday, with the results below. A new poll has been opened for the potential Christmas storm, please vote your thoughts on that poll, which will close on Thursday.

5 votes - Storm well to the south, dry and cold
10 votes - Storm clips NYC with light snow
4 votes - Heavy snow and wind in NYC
2 votes - Too close to coast, rain/snow mix

------------------------------------------------

Today brought increasing clouds to the area as a storm to the south brought rain and some frozen precipitation to the Southeast. Despite this being the short range, I am now keeping an eye on the possibility that the storm tracks further west than currently expected, with perhaps some snow accumulations in Long Island tomorrow.


Tomorrow's Storm: Snow In Long Island?

Yesterday, it became apparent that the storm would fail to impact places near and west of NYC with anything more than a few flakes, if even that. The latest short term models, however, are catching on to the possibility that the storm may try to move NNE up the coast, bringing 1-2 inches of snow to Long Island and even more snow for Cape Cod, eastern Massachusetts and Maine, while models such as the GGEM and GFS do not show this scenario.

With this being in the near future, it is coming down to simple observations such as the radar and where the storm is tracking to determine whether the solution that the short range models are showing may verify or not. At this time, I went with a 70% chance of snow in Long Island with potential accumulations up to 1 inch, but this is based on the possibility of the storm tracking further west. This change, however, would have very little impact on the rest of the area, with NYC only seeing flurries with the western parts of the area staying dry.

Stay tuned for an update tomorrow morning about this possibility, and a Light Snow Alert may be needed for eastern Long Island if the storm does track further west than originally expected.


Tuesday-Wednesday Clipper: No Snow Expected

Yesterday, the potential of a weak clipper affecting the Mid Atlantic was discussed, with some uncertainties that have been mostly eliminated with today's models. The clipper is expected to significantly weaken east of the Appalachians, and bring some light snow to the central Mid Atlantic, including Washington DC, between Tuesday and Wednesday with the area staying dry. I did, however, mention the potential of flurries in the 5-Day Forecast.

Temperatures will slowly warm up through this time frame, with Wednesday's high temperatures the warmest over the next week or so, peaking in the mid 30s inland, mid to upper 30s in the immediate NYC area, and upper 30s for Long Island/S CT. A few places in the central and eastern parts of the area may reach the 40 degree mark.


Thursday - Sunday: Dry Start, Potential Christmas Storm

Thursday and early Friday are expected to be dry once again for the area as the effects of tomorrow's storms will end as the storm, still expected to be off the coast early in the week, will move away from the region. More sunshine is expected with temperatures generally remaining steady, slightly cooling down from Wednesday. Meanwhile, another storm is expected to start taking shape in the central US, moving towards the region.

The models today have backed away from the big snowstorm solution that the GFS had yesterday, with most of them showing a snowstorm well to the south of the area. This is still in the long range, however, and while it is possible that the storm does stay to the south of the area, it is also possible that the storm trends north to affect the area. The difference with this storm and the previous one, however, is that there are less players coming into play with the scenario, so it appears that the models may have an easier time handling this storm than tomorrow's storm, when we're less than a day from the storm and there is still some uncertainty.

At this time, it is likely that a storm will be moving west to east through the central US during this time frame, which would then bring at least some snow to the central and potentially southern Mid Atlantic, but what happens from there is a question, as it is possible that the storm moves ENE and out to sea, or it could intensify and move NE up the coast, bringing a big snowstorm for the coast or into the Interstate 95 corridor.

Details are uncertain at this time, however there is the potential of a storm to affect the region during this time frame with snow, and may potentially affect the area. Stay tuned for more information about this storm.

Friday, December 17, 2010

Dec 17: Sunday Snow Unlikely, Looking Ahead

Notes:

- The 5-Day Forecast was updated for the entire area, with a new 5-Day Graphic.

- The Snow Alert has been removed for the eastern parts of the area. More information on that is below.

----------------------------------------------

Today was a partly cloudy day across the area with slightly warmer temperatures than those of yesterday, which continues the warming trend from earlier this week when high temperatures were barely in the 20s.

Tomorrow will be a mostly sunny day with more clouds by the afternoon with a west wind. High temperatures will be in the lower 30s inland and in the mid to potentially upper 30s across the rest of the area. A storm will affect the Southeast with rain and some snow, however it now appears that the storm will miss the area with nothing more than flurries across the eastern parts of the area.


December 19-20 Storm: Now Likely To Stay East Of NYC

It first appeared that a storm potential existed for this time frame on Sunday, when I mentioned it in my discussion. The following day, the GFS model jumped on board, showing a blizzard for the area. Over the last few days, however, the models trended east, and despite yesterday's afternoon runs, which briefly went west again to show some light snow for NYC, today's models continued trending east, and are now in agreement with any snow staying south/east of NYC.

The models are also starting to become much more consistent with the storm, meaning that while some minor shifts are expected, a trend big enough to put the NYC area in the potential area of several inches of snow is very unlikely to happen. This was a very possible solution all along, which was the reason why I kept the minimum potential snowfall at 0 inches in case this scenario would verify, which now appears to be the likely scenario.

The models now show a much weaker and further south storm by Sunday morning, which ends up southeast of Cape Hatteras, NC, slowly intensifying and moving NE. The models yesterday had the storm already steadily intensifying with a negative tilt moving NNE by this time, however today's consensus shows a weak storm further east still moving NE and only slowly intensifying. The storm becomes more intense by Monday, however by then it is already well northeast of the area. Based on this scenario, I removed snow chances for the interior and only kept a chance of flurries in the NYC area in case the storm trends slightly more west, though if there's no changes in the forecast that chance will likely be removed tomorrow.

Looking at the temperatures for the area, since we're not looking at much, if any precipitation for Sunday, temperatures will be slightly warmer than previously expected, in the lower to upper 30s across the area, and low temperatures on Sunday night could be cold again, in the mid 10s inland and upper 10s to mid 20s in the NYC area. Monday will be a partly cloudy and breezy day with slightly colder temperatures, in the upper 20s to mid 30s.


Tuesday - Wednesday: Clipper Brings Light Snow Potential

The storm that will miss the area to the east this weekend is expected to end up in the Atlantic Ocean away from Nova Scotia by Tuesday, however another clipper is expected to be near the Ohio Valley, moving east or ESE towards the Mid Atlantic and southern Northeast. There are differences with the timing and the location of the weekend storm, which will influence what this storm might do, however it appears that this storm may have the potential of bringing light snow to the area between Tuesday night and Wednesday.

It is possible that the storm stays south of the area with only light snow in the central Mid Atlantic, another possibility is that the storm is further north and stronger, and brings a period of steady snow to the area. At this time, I am leaning towards the southern solution, with some light snow in the central Mid Atlantic and perhaps some snow showers in the area. Regardless of the storm scenario, however, it appears that the storm may end up being absorbed into the larger storm to its east, which would prevent this from becoming a notable snow producer east of the Appalachians, however this potential is also uncertain and could change. More information on this clipper will be posted over the next few days.


Thursday - Sunday: Cold And Dry Start, Potential Christmas Storm?

By Thursday and Friday, once the previous storm exits the region, dry conditions with less cloud cover are expected once again, and temperatures are expected to remain chilly and generally steady in this time frame. By Saturday, however, the latest model runs have been showing a potential storm, which would be a clipper moving east through the central US and affecting the area. The GFS model was the most aggressive with this potential, with its 18z run showing over 6 inches of snow for NYC. As this is in the longer range, it is too early to look at the specific details of the storm, such as where it tracks and where snow falls, however there is the potential for a storm during this time frame that needs to be watched. Stay tuned for more information on this potential storm and how it may affect the area.