Tuesday, November 30, 2010

Nov 30: Rain Moves In

Due to technical difficulties, a full update will not be posted tonight. The 5-Day Forecast page was not updated, though for the main part the expectation remains the same with very little changes.


Tonight And Tomorrow: Storm Brings Rain, Wind, Thunderstorms

An unexpected round of light rain developed earlier today as the storm started affecting Pennsylvania, as the storm was not supposed to bring widespread rain to the area until at least tonight. Rainfall amounts were generally light from this round of rain, and it is currently cloudy across the area. A warmer air mass is currently moving into the area, with 850 mb temperatures expected to reach 10c by tomorrow morning. As a result, temperatures will steadily rise tonight, reaching the mid to upper 50s by the morning. Occasional showers will fall tonight, however the heaviest rain will hold off until tomorrow. In addition, expect winds to increase tonight, coming out of the SSE.

The line of heavy rain and thunderstorms we are currently seeing affecting the eastern Ohio Valley will move into the area by tomorrow, affecting the area from west to east between the morning and the evening hours. This will produce heavy rainfall, strong winds gusting near or over 50 mph, and thunderstorms as well. Rainfall amounts are expected to range from 1.5 to 2.25 inches inland, 1 to 2 inches in the immediate NYC area, and 3/4 to 1.5 inches in Long Island/S CT. The winds should calm down by the overnight hours, but breezy conditions will likely continue.


Longer Range Outlook: Cold Pattern Settles In, But Will Snow Fall?

Between Thursday and Saturday, the forecast remains the same as yesterday. A cold air mass moves into the area, which given the -NAO is expected to settle in and not quickly exit like previous cold air masses have done.

By Sunday, however, uncertainty increases. With yesterday's update, I mentioned how a clipper could produce snowfall for the Mid Atlantic. Today's models, however, backed away from the clipper, and the models that do show the clipper have it very weak and dissipate it west of the Appalachians. As this is over 100 hours out, and the models are not consistent yet, changes are expected with the solution, and it is possible that the models trend back to the clipper solution with snow in the Mid Atlantic, however at this time, it is starting to look less likely that we see a scenario like the one mentioned yesterday. Stay tuned for more details on this potential over the next few days.

Afterwards, the models continue to show a strong -NAO with several consecutive retrograding storms hitting Maine and Nova Scotia while cold air stays trapped over the region. While there is also uncertainty with this solution, it does seem likely that at least for the first 1-2 weeks of December, a cold pattern will be in place, with temperatures below average, potentially bringing highs in the 30s for the area and lows in the 20s with 10s inland. The question at this time is whether the pattern can become favorable for snow events, as the current scenario that the models are showing suppresses any storm that tries to develop. Stay tuned for more details on this time frame.

Monday, November 29, 2010

Nov 29: Snow Potential On December 5

Note: A new poll has been opened for the potential scenario on 12/5 and whether it snows or not. Please vote your thoughts in the poll, which will close on Friday.

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Today was a mainly sunny day across the area, with high temperatures peaking in the mid to upper 40s inland, upper 40s to lower 50s in the immediate NYC area, and in the mid to upper 40s in Long Island/S CT. This morning was a cold one across the area, with low temperatures as low as the mid to upper 10s inland due to radiational cooling. Temperatures are currently steadily droppping across the area, however with increased cloud cover expected for tonight, the low temperatures will take place early in the overnight hours with warmer temperatures by tomorrow morning.

Temperatures will continue to warm up through Wednesday, when they should peak in the upper 50s to lower 60s ahead of a storm that will produce heavy rain, thunderstorms, and very windy conditions. A much colder pattern will settle in behind this storm, and afterwards we may be looking at the first widespread snow event for the Mid Atlantic by Sunday through Monday.


Tomorrow's Outlook:

Tomorrow will be a mostly cloudy day across the area with a SE wind expected. High temperatures will be in the lower 50s inland, lower to mid 50s for the north/west suburbs of NYC, mid 50s in NYC, and in the lower to mid 50s for Long Island/S CT.

Looking at the rest of the region, the Mid Atlantic should warm up, with southern/eastern Virginia reaching the mid to upper 60s. Rain is expected to start falling in Pennsylvania and western New York, however any rain will stay to the west of the area until Wednesday.


Tomorrow Night - Wednesday: Becoming Windy, Stormy

Cloudy skies are expected tomorrow night as the cold front produces heavy rainfall in Pennsylvania/New York, with an occasional shower possible late for the western and central parts of the area. As a warm air mass moves into the area, with 850 mb temperatures rising to near 10c, temperatures will rise overnight, reaching the mid to upper 50s across most of the area by Wednesday morning. Windy conditions are also expected to develop overnight, with gusts near/over 40 mph possible, being why a Wind Alert is in effect for the area.

On Wednesday, a line of heavy rain and thunderstorms, potentially strong/severe south of NYC with damaging wind gusts the main risk, will move through the area from west to east, affecting the western parts of the area in the morning/afternoon and the eastern parts of the area in the afternoon/evening. By the time that the rain ends, at least 1.5 to 2.5 inches of rain are possible inland, 1 to 2 inches in the immediate NYC area, and 3/4 to 1.5 inches in Long Island/S CT. More updates on this storm will be posted tomorrow, as well as a final rain map.


Thursday - Saturday: Colder, Breezy

The cold front will move through the area on Wednesday night, with a negatively tilted trough moving into the area for Thursday. This trough, unlike the previous ones we've seen this fall, is expected to settle in, with a strong -NAO present, leading to persistent chilly conditions and mostly cloudy skies. High temperatures in this time frame will be in the upper 30s to mid 40s, with lows in the lower 20s to lower 30s.


Saturday Night - Monday: Potential Snow Event For Mid Atlantic

Over the last several days, the potential for a storm on December 4-6 was mentioned. While the GFS model is still not showing this scenario, it is still having difficulties handling the pattern and will likely start to show the storm soon. We are looking at a clipper from the north central US that will be moving ESE, and with the strong cold over the NE US and the -NAO, will track to the south of the area. With plenty of cold air available, this storm will likely produce snow to its north, even in the central and northern Mid Atlantic, between Saturday night and Sunday night.

While there still some uncertainty with the timing and the track of the storm, it is likely that there will be a clipper, and its track could range from southern Virginia to near Washington DC. At this time, the models are showing the southern track, with the heaviest snowfall between Washington DC-Philadelphia, but there is still time for trending and is it possible that the storm trends further north. With the potential scenario mentioned above, snow is likely to fall in at least the central and northern Mid Atlantic on Sunday, potentially including the NYC area, which will generally be light but may accumulate up to several inches where the heaviest snow falls. At this time, the potential snow area labeled on the map to the top is from central Virginia to southern New England, though this range will likely become narrower as the storm enters the shorter range. Stay tuned for more details on this potential storm and how it may affect the area.


After the storm exits the region, there is increasing uncertainty, however it is likely that the storm will intensify offshore once it exits the region by Monday. It appears that with the -NAO in place, the storm could get a negative tilt offshore, and according to the ECMWF model, may try to move back NW towards New England. There is a lot of uncertainty about what happens with the storm though, so stay tuned for more details over the next few days.

Sunday, November 28, 2010

Nov 28: Wednesday Storm, Longer Range Outlook

Notes:

- The 5-Day Forecast was updated tonight.
- The poll for this winter's temperatures and snowfall in NYC ended yesterday. Here are the final results:

Temperatures: (Total 39 votes)

1 vote - Well above average (>+5)
5 votes - Above average (+3 to +5)
9 votes - Slightly above average (+1 to +3)
10 votes - Average (-1 to +1)
12 votes - Slightly below average (-1 to -3)
1 vote - Below average (-3 to -5)
1 vote - Well Below average (-5+)

Snowfall: (Total 41 votes)

4 votes - Well below average (<12")
4 votes - Below average (12" - 18")
8 votes - Slightly below average (18" - 24")
9 votes - Average (24" - 28")
10 votes - Slightly above average (28" - 34")
2 votes - Above average (34" - 40")
4 votes - Well above average (40"+)

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Today was a mostly sunny and chilly day across the area, with high temperatures in the mid to upper 40s inland, upper 40s to lower 50s in the immediate NYC area, and in the mid to upper 40s in Long Island/S CT, which was slightly warmer than expected. Temperatures this morning were cold, in some places the coldest so far this fall, with widespread lower 20s inland and most places away from NYC dropping into the 20s.

Tonight will be another cold night, with clear skies and temperatures already dropping steadily across the area, though tomorrow will be even warmer, with lower 50s returning into the immediate NYC area. Temperatures will continue to warm up until Wednesday, when a storm will end the warmth with strong winds, heavy rainfall and thunderstorms.


Tomorrow's Outlook:


*Slight revision: The 50-55 degree area is extended further out to cover western Long Island and most of NE NJ.

Tomorrow will be another mostly sunny day across the area with calm winds becoming a light SSE wind. High temperatures will be in the mid to upper 40s inland and in the upper 40s to lower 50s for the rest of the area.


Tuesday - Wednesday: Significant Storm To Affect The Area

**NYC Area Weather currently has 3 alerts in effect: A Rain Warning, Rain Watch, and a Wind Alert. Please check the Weather Alerts page for the latest alerts in your area.**


Tuesday is expected to be a mostly cloudy day for the area, with high temperatures in the lower to upper 50s across the area. A cold front in the Ohio Valley will approach the area slowly, leading to rain developing in Pennsylvania and a few showers potentially reaching NW NJ in the evening hours.

On Tuesday night, the cold front will move towards Pennsylvania, with a wave of low pressure expected to develop along the front. Tuesday night will be cloudy for the area with a few showers possible, especially in the western parts of the area and later in the overnight hours, though winds are expected to increase. As the storm draws in a warmer air mass, temperatures will steadily rise overnight, reaching the mid to upper 50s inland and in Long Island/S CT, with upper 50s in the immediate NYC area.

The cold front will move through the area on Wednesday, bringing heavy rainfall. A line of heavy rain and thunderstorms will move from west to east, affecting the western parts of the area during the morning/afternoon hours and the eastern parts of the area in the afternoon/evening hours. Windy conditions are expected, with even stronger wind gusts possible with any heavier rain shower/thunderstorm. As a result, it is possible that the Wind Alert may be upgraded to a High Wind Watch.

By the time that the storm is over on Wednesday night, rain totals should range from 1 to 2, locally 3 inches in the western and central parts of the area, with 3/4 to 1.5 inches further east. The rain map created yesterday remains unchanged and may be used as the final rain map.


Longer Range: Colder, Potentially Snowy Pattern Setting Up

On Thursday, after the cold front moves through, a negatively tilted trough will move into the area, bringing low temperatures back into the 20s and high temperatures into the upper 30s to mid 40s. This time, however, it appears that the trough may stick around in the area through at least Saturday, keeping these cold temperatures in place.

By Sunday, there is more uncertainty on the time frame, however with the GFS considered as an outlier and not used for this update as it is still having difficulty handling the pattern, it appears that a low pressure from the west, potentially an Alberta Clipper, will move west to east through the United States, potentially moving through the Ohio Valley. This potential clipper will likely stay to the south of the area given the cold air and the -NAO in place, and while it is possible that like the GGEM/DGEX models are showing, the clipper may be moisture starved and may not be able to make it further east than the Appalachians, if this storm is stronger and does make it east of the Appalachians, it is possible that there could be a little snow in the area on Sunday. Stay tuned for more details on this potential storm.

For the longer range, however, the currently strong -NAO is expected to weaken afterwards but is still expected to remain negative, and while there is a lot of uncertainty for this time frame, it is possible that the pattern may become more favorable for snow events affecting the area after December 5. More on this potential will be discussed over the next few days.

Saturday, November 27, 2010

Nov 27: Heavy Rain And Wind On Wednesday

Note: The 5-Day Forecast was updated for the entire area tonight.

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Today was a partly cloudy day across the area with chilly and breezy conditions, with high temperatures in the upper 30s to lower 40s inland and in the lower to mid 40s for the rest of the area. Temperatures this morning were cold, but not as cold as expected due to more cloud cover than expected, with NYC failing to drop below the freezing mark. Temperatures are currently dropping very slowly across the area, but with clear skies and a high pressure, temperatures tonight should be cold again, and will likely be colder than those of this morning.

Temperatures should start warming up by Monday, with a storm expected to bring widespread heavy rain, windy conditions and potentially thunderstorms on Wednesday, being why I have a Rain Watch, or a 30-70% chance of rainfall amounts near or over 1 inch in effect for the central and western parts of the area. Temperatures should cool down again behind this storm, with the pattern setting up for what could be an active period of time in the longer range.


Tomorrow's Outlook:

Tomorrow should be a mostly sunny day across the area with a light WNW to NW wind expected. High temperatures will be in the lower to mid 40s inland and in the mid to upper 40s for the rest of the area.

Looking across the rest of the region, high temperatures should be slightly warmer than those of today, in the 30s to lower 40s and some 20s in the higher elevations. The southern Mid Atlantic should be slightly cooler, with highs in Washington DC and Virginia in the upper 40s to lower 50s.


Monday: Warming Up

On Monday, a low pressure near the Midwest and an exiting trough in the region should lead to warmer temperatures in the area. High temperatures will peak in the mid to upper 40s inland and in the upper 40s to lower 50s in the immediate NYC area, however temperatures will only continue to get warmer from this point through Wednesday.


Tuesday - Wednesday: Storm Produces Heavy Rain, Wind

On Tuesday, a strong low pressure should be present near the Great Lakes, moving NNE and bringing a cold front through the Ohio Valley and the Southeast, slowly moving east. This front will be capable of producing heavy rainfall and potentially strong/severe thunderstorms. For the scenario map on Tuesday, please refer to the map posted on the November 25 update.

Overnight on Tuesday, the storm will approach the area, with a wave of low pressure forming along the boundary and enhancing the rainfall around Pennsylvania. Tuesday night will be mainly cloudy for the area with rising temperatures as a warm air mass moves into the area, and rain increasing in intensity by the morning.

As the warmest air mass will be over the area on Wednesday, with 850 mb temperatures above 10c, high temperatures will peak in the upper 50s inland, and in the lower 60s in the immediate NYC area. Heavy rain will fall, mainly in the second half of the day, along with windy conditions. Some thunderstorms are also possible on Wednesday. By the time that the rain ends on Wednesday night, rain totals could range from 1 to 3 inches of rain across the area. Stay tuned for more details on this storm.


Longer Range: Cold End To Week, Storm Potential To Follow

After this storm, a much colder air mass should move into the area for Thursday and Friday. While it is uncertain how cold it gets, it appears that the cold air mass could be locked up over the area until at least Saturday, which if this scenario verifies, temperatures could be even colder than today and tomorrow, with high temperatures in the mid 30s to lower 40s and low temperatures in the upper 10s to upper 20s possible. These numbers could change over the next few days, so stay tuned for more details.

Those who have been watching the long range GFS model have been seeing crazy solutions showing up on the model, with several consecutive large storms affecting the Northeast after December 4-6, with cold air trapped over the area. The GFS seems to be incorrectly handling the pattern, and will likely change over the next few days. The ECMWF is showing a low pressure moving west to east across the United States, with redevelopment off the coast and potential for frozen precipitation in the northern Mid Atlantic. The models are all over the place with this storm as they are having difficulty handling the pattern, though it is likely that a storm should be present in this time frame and could affect the area. Stay tuned for more details on this potential storm and how it may affect the area.

Friday, November 26, 2010

Nov 26: Cold Weekend, Rain Returns For Tue-Weds

Today started out cloudy and wet for the area, with light rain associated with the cold front falling, and as the cold front cleared the area, the skies started to clear by the late afternoon, with high temperatures in the upper 40s inland and in the lower to mid 50s for the rest of the area. With mainly clear skies now in place, temperatures are quickly dropping across the area, and are already in the lower to upper 30s away from NYC. Tonight is expected to be the coldest night so far this fall, with lows in the upper 10s to lower 20s inland, mid to upper 20s for S CT and the north/west suburbs of NYC, in the upper 20s to lower 30s in Long Island, and in the lower to potentially mid 30s in NYC.

Tomorrow will be a chilly day for the area, with highs in the upper 30s to mid 40s, however temperatures will continue to warm up through the weekend into Wednesday, when a storm affecting the area could result in heavy rainfall over 1 inch.


Tomorrow's Outlook:



Tomorrow will be a mostly sunny day across the area with a west wind expected. Temperatures will be chilly, peaking in the upper 30s to lower 40s inland, lower to mid 40s north and west of NYC, mid 40s in NYC, and in the mid to potentially upper 40s in Long Island/S CT.

Looking at the rest of the region, tomorrow should also be a cold day across the Northeast, with high temperatures generally in the 30s to lower 40s, with 20s in the higher elevations of the central/northern Northeast. The central/southern Mid Atlantic should still be chilly but not as cold, with Washington DC in the upper 40s and Virginia in the lower 50s.


Sunday - Monday: Dry, Not As Cold

On Sunday, the trough will start to weaken, however it will still be strong enough to produce another day of cold temperatures, but slightly warmer than those of tomorrow, peaking in the lower to mid 40s inland and in the mid to upper 40s for the rest of the area.

Sunday night will be another cold one with mainly clear skies in place, though Monday will continue the warm up as the trough exits the area and a low pressure organizes itself near the Midwest, with high temperatures returning into the lower 50s for the immediate NYC area.


Tuesday - Wednesday: Heavy Rain, Wind Potential

On Tuesday, a low pressure will organize itself over the Great Lakes, with a cold front moving through the Ohio Valley and the Southeast, associated with heavy rainfall. This cold front will then move towards the area pulling in a warmer air mass, resulting in temperatures rising through Tuesday night, peaking on Wednesday in the upper 50s to lower 60s with windy conditions possible. Meanwhile, a wave of low pressure will develop along the front, producing heavy rain for the area on Wednesday, with over 1 inch of rain likely for most of the area. At this time, I issued a Rain Alert for the area, indicating a less than 30% chance of 1+ inch of rain, however this will likely be upgraded to a watch tomorrow.

The heaviest rain from this storm is expected to be inland, west of the area, where over 3 inches of rain could fall, however there is the potential of 1 to 2 inches of rain for most of the area, with locally 3 inches of rain for the western and potentially central parts of the area. Stay tuned for more information on this storm.


More on the longer range will be posted tomorrow, including a cool down behind this storm and another storm expected for December 4-6.

Thursday, November 25, 2010

Nov 25: Storm Summary, Longer Range Update

Today ended up bringing the second snow/sleet event to parts of the area, as a storm approaching from the west led to several hours of snow/sleet falling west of NYC before changing over to rain.

The set up that took place today was already clear over the last several days, with the general idea of wintry precipitation, potentially accumulating, in most of PA into northern New Jersey, however there were some small uncertainties with the timing which led to some differences with the forecasts, as the NAM model was the slowest, bringing precipitation in only after 5 PM, and was correctly considered as a slow outlier for this storm as it tends to have a slow bias.

Today, we saw a broad area of low pressure from the Midwest into the Ohio Valley moving east, with the front end of the storm entering Pennsylvania in the early overnight hours, bringing heavy precipitation. Dew points were low across the Northeast, meaning that evaporative cooling, temperatures cooling down once precipitation starts, would take place. With a high pressure exiting the region, a Cold Air Damming scenario took place, where cold air was trapped over Pennsylvania despite the storm track, which would usually support a much warmer air mass. While surface temperatures in most of PA were cold, there was a small area of 850 mb temperatures below zero in central Pennsylvania, leading to heavy snow developing in those areas and moving east during the morning hours into eastern PA along with the pocket of sub-zero 850 mb temperatures.

The heavy snow in eastern Pennsylvania was a result of the factors mentioned above, and at least a period of moderate snow fell over most of eastern PA as well as southern and central New Jersey. The best dynamics were over eastern PA, where heavy snow for several hours accumulated up to 2-3 inches, with reports of slightly over 1 inch in Allentown. As the pocket of cold 850 mb temperatures was further east over eastern PA, central/western PA changed over to rain/freezing rain by the late morning.

As the precipitation pushed east into the dry air by the early afternoon, it began to weaken, leading to the dynamics becoming less favorable and the area of snow shrinking. Light snow/sleet managed to fall over northern New Jersey, with sleet mixing in with the rain in Bergen County and New York City. By 5 PM, 850 mb temperatures then went back above 0c, and with temperatures warming up, the area changed over to light rain.

As of 10 PM, the area is seeing cloudy skies and warm air advection starting to take place, with temperatures expected to rise tonight, however an area of heavy rain in western NY/PA associated with the cold front of the storm will lead to a wet start to Friday, followed by a cold weekend.


Tomorrow's Outlook:

As the main storm will be north of the Great Lakes with a secondary low developing near Maine, a cold front will move through in the late morning hours, producing moderate rain late tonight into tomorrow morning, though the heaviest rain should be to the north of NYC. By the early afternoon, the cold front should clear the area, with clearing skies, and breezy conditions. High temperatures will be steady in the mid to upper 40s inland and lower to mid 50s for the rest of the area, dropping by the late afternoon.

With mainly clear skies and a much colder air mass tomorrow night, temperatures should quickly drop overnight, with the coldest temperatures so far this fall possible by Saturday morning, in the upper 10s to lower 20s inland, mid to upper 20s in S CT and the north/west suburbs of NYC, upper 20s to lower 30s in Long Island, and in the lower 30s in NYC.


Weekend Outlook: Dry, Cold

Saturday should be a very chilly day, with high temperatures expected to be in the upper 30s to lower 40s inland and in the lower to mid 40s for the rest of the area. Saturday night will have mainly clear skies again, but with a slightly weaker cold air mass, should be a little warmer than Friday night. Sunday should be warmer, with high temperatures in the lower to mid 40s inland and in the mid to upper 40s for the rest of the area, but with a high pressure in place and clear skies, Sunday night could be slightly colder than Saturday night.


Early To Mid Week Outlook: Storm Expected For Wednesday

As the high pressure exits the area and a low pressure moves through the Midwest, the trough will lift out of the Northeast on Monday with temperatures returning into the 50s for parts of the area. This storm will pull in an arctic air mass into the Dakotas, though not as strong as the one we saw over the last few days, and its cold front will start to slowly move east. On Tuesday, the storm should be north of the Great Lakes, with a large supply of cold air to its west and a slow moving cold front moving through the Ohio Valley and the Southeast, pulling in a warm air mass into the East along with heavy rain. On Tuesday, due to the high pressure to the NE of NYC, the air mass won't get as warm as places to the west/south, however that will change in the overnight hours.

By Wednesday, a low pressure is expected to develop along this cold front, and while there is uncertainty on the exact track, it could end up between western Pennsylvania and a track just off the coast, taking a negative tilt overnight and moving more north, then NNW through the Northeast as cold air comes rushing into the southern side of the storm. This storm has the potential of producing heavy rainfall over an inch in the area, as well as the potential of a snowstorm to its west, further inland. Stay tuned for more details on this storm.


Longer Range: Colder, Then Another Potential Storm For December 4-6

Behind the storm, a moderated version of the arctic air mass will move into the region, producing yet another round of cold temperatures, potentially similar to those of this coming weekend for Thursday and Friday, however another storm will meanwhile be taking shape near the Rockies.

Even though there is uncertainty as this is in the long range, it appears that a storm could be moving east through the central US during this time frame. With another potential arctic air mass dropping into the north central US, this potential storm will be capable of producing snow to its north, affecting the area on the 5th and 6th. Due to a -PNA still in place, this storm is also likely to track inland to the north of the area, however the models are suggesting that if the storm does track inland, with a -NAO still in place, there could be redevelopment further east, however at this time, this time frame doesn't appear to be favorable for a snowstorm in the northern Mid Atlantic. Stay tuned for more details on this time frame.

Nov 25 Storm Updates

***NYC Area Weather has issued a Sleet / Freezing Rain Alert for Sussex and Orange Counties, in effect until this evening.***


Below, storm updates will be posted on the storm, which is expected to bring the second snow/sleet of the season to the central and western parts of the NYC area.

**Short term outlook maps will also be posted, click on the maps to view them in a larger size.**

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5:00 PM: The snow/sleet part of the storm has ended for the area, as warm air advection is changing over any snow/sleet into rain and freezing rain in the higher elevations. The storm updates have ended for today. Stay tuned for an update later tonight about the longer range.


2:10 PM: Snow/sleet fell earlier this afternoon over much of central New Jersey and NW NJ, however due to the low dew points, the precipitation had difficulty moving further north, and light rain is now falling over NYC with sleet mixing in parts of Bergen County. While the dynamics aren't as favorable as they were earlier this morning, there's heavier precipitation in north central NJ moving east, which should result in sleet/wet snowflakes mixing in with the rain in the areas mentioned above, with another round of snow/sleet for north central and NW NJ.

Behind this area of heavy precipitation, expect the snow in NW NJ to gradually mix with and start to change over to sleet/rain.


11:40 AM: We are currently seeing heavy precipitation falling in Pennsylvania, with the eastern edge curving ESE into northern Delaware and southern New Jersey. Last night, snow/sleet fell over much of Pennsylvania, and as the cold air mass is moving out but the cold air is still trapped, the snow/sleet is now falling as rain/freezing rain in places that saw snow last night.

With the scenario mentioned last night, the front edge of the precipitation is now in western New Jersey and moving east. Due to the cold 850 mb temperatures and low dew points, evaporative cooling is taking place, meaning that despite temperatures appearing to be too warm for snow in northern New Jersey, they will drop once precipitation starts to fall, leading to snow, mixing with sleet at times.

There is already snow/sleet falling in parts of New Jersey and even Philadelphia, with accumulating snowfall reported in eastern Pennsylvania. As precipitation continues to move east, so will the rain/snow line, which should lead to snow/sleet falling over most of northern New Jersey by at least 12-2 PM, with accumulations up to 1/2 inch possible inland.

Wednesday, November 24, 2010

Nov 24: Final Forecast For Tomorrow

Notes:

- The 5-Day Forecasts have been resumed for Long Island/S CT. Check the 5-Day Forecast for the how the storm tomorrow may affect your area, and how cold it could get over the weekend.

- The winter polls will be closing on Saturday. Please vote if you have not done so yet.

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Today was a mostly sunny day across the area, though temperatures were much colder than those of yesterday, with high temperatures in the mid to upper 40s inland and in the upper 40s to lower 50s in the immediate NYC area, which was slightly warmer than expected.

Clouds are increasing in the area as a storm is moving in, currently producing a wintry mix in the Ohio Valley into SW Pennsylvania, and this storm should continue to move towards the area, likely bringing the second snow/sleet of the winter to places west of New York City for Thanksgiving.


Thanksgiving Day Scenario / Forecast:

Temperatures are expected to be quite chilly tonight, in the mid 20s to lower 30s away from the coast, as a cold air mass starts to leave the region and the front end of the storm starts to move into Pennsylvania. As a high pressure will be exiting the area, however, cold air will be trapped in Pennsylvania, leading to a CAD, or Cold Air Damming, set up. Dew points are currently low across the Northeast, and are expected to be in the 20s tomorrow when the precipitation begins to fall, which will lead to evaporative cooling, or temperatures dropping into the upper 20s to lower 30s as precipitation starts to fall in Pennsylvania. With 850 mb temperatures slightly below 0c, this will lead to a widespread wintry mix in Pennsylvania, southern NY and northern NJ, which could accumulate in PA given the heavy amounts of precipitation expected.


Forecast for NYC area: In the area, precipitation will not be as heavy, however some snow and sleet are still expected west of New York City. High temperatures are expected to peak in the late morning for the western parts of the area and in the early-mid afternoon for the eastern parts of the area, in the mid to upper 30s further west, upper 30s to lower 40s in the immediate NYC area, and in the lower to mid 40s for Long Island/S CT.

As mentioned previously, due to the low dew points, temperatures will drop once precipitation starts to fall around 1-3 PM. The drop in temperatures will be the most noticeable further west, where temperatures by the late afternoon will drop into the lower 30s with snow and sleet likely to fall, potentially accumulating between a trace and 1/2 inch in the faster scenario. In the immediate NYC area, temperatures will likely drop into the upper 30s, with some snow/sleet expected west of NYC. There shouldn't be much of a drop in Long Island/S CT, which will see mainly cloudy skies with a few showers possible in the late afternoon.

Note, however, that there is still some uncertainty with the storm for tomorrow, and it is possible that the storm may be a little slower than expected, like the NAM/00z GFS models are showing. If this verifies, temperatures could be several degrees warmer in the area, with the main precipitation type being rain with maybe a few flakes inland. Stay tuned for storm updates that will be posted throughout the day tomorrow.


Thursday Night - Friday: Rising Temps, Then Cold Front Moves Through

On Thursday night, warm air advection will take place, pushing out the small area of cold air and changing over any frozen precipitation in the northern Mid Atlantic into rain. Light rain will continue to fall across the area overnight with rising temperatures, though there could be some dry periods overnight. Temperatures will rise into the lower to mid 40s inland, mid to upper 40s in the immediate NYC area and in the upper 40s to lower 50s for Long Island/S CT.

On Friday, the cold front will move through, producing a round of moderate rain for the area. Temperatures will be steady in the morning to early afternoon, and should drop in the late afternoon once the cold front moves through with increasing winds. Low temperatures will be much colder overnight, ranging from the lower-mid 20s inland to the lower-mid 30s in NYC.

Saturday - Sunday: Cold, Breezy

The coldest air mass so far this fall will move into the area behind the cold front, producing much colder temperatures. High temperatures on Saturday will struggle to reach the 40s across most of the area, peaking in the upper 30s to mid 40s, with overnight lows cold again, similar to, if not slightly warmer than those of Friday night.

Sunday should warm up a little, with highs in the lower to upper 40s, but with clear skies, overnight lows could be slightly colder away from the coast. Monday will continue the trend, with high temperatures returning into the 50s in the immediate NYC area.


Stay tuned for more details on the longer range, including a storm on Tuesday and Wednesday which will bring warmer temperatures and the potential of moderate-heavy rain which will be followed by colder air, and another potential storm around December 4-6.

Tuesday, November 23, 2010

Nov 23, 2010: Wintry Mix Potential On Thanksgiving

Today was a mostly cloudy day across the area, with high temperatures in the mid to upper 50s inland, lower to mid 60s in the immediate NYC area, and in the upper 50s to lower 60s in Long Island/S CT, which was near the expectation.

A colder air mass is going to move into the area tonight, bringing much colder temperatures for tomorrow, with high temperatures returning into the 40s. Even though a storm moving through the Great Lakes will affect the area on Thursday and Friday, it appears that the cold may stay long enough for precipitation to begin as a wintry mix west of New York City.


Tomorrow's Outlook:

Tomorrow will be a mostly sunny and colder day, with a NW wind expected. High temperatures will be in the lower to mid 40s inland with a few upper 40s possible and in the mid to upper 40s for the rest of the area, with a few lower 50s possible south and SW of NYC.

Looking at the rest of the region, tomorrow will be a cold day in the interior Northeast, where highs will only be in the 20s to the lower 30s. Virginia will see highs in the lower to mid 50s.


Thanksgiving Storm: Wintry Mix To Rain

While at first, the models were not consistent with the storm, in fact the GFS model was showing a very weak and suppressed storm solution at one point, the models came into better agreement on Sunday, which is still present, though there is still some uncertainty with the timing of the storm. Below, I will discuss the expected set up for the storm and the forecast for this time frame.


Storm Set Up: A broad area of low pressure tomorrow expected to be near Kansas will split by tomorrow night into Minnesota with another low pressure further south, which the Minnesota low pressure becomes the dominant one by Thursday and intensifies while moving ENE. Unlike a typical storm in that area, however, the low pressure will expand southeast while becoming negatively tilted, and redevelopment is expected near the New England coast on Thursday night moving NNE towards the main storm. This redevelopment potential was already shown on the models for the last several days. The storm will bring its cold front through on Friday for most places, with a much colder air mass including scattered flurries behind it.


Thursday: As the storm moves into the area in the late morning hours, surface temperatures will be in the lower 40s inland and lower to mid 40s in the immediate NYC area. Dew points are expected to be in the 20s, with a high pressure over the area moving east. A CAD (Cold Air Damming) scenario is expected to take place, where despite the storm moving into the Great Lakes, instead of bringing a warm air mass into the region, it traps some cold air in Pennsylvania, with a small area of 850 mb temperatures below 0c.


With the set up mentioned above, a band of precipitation will move into Pennsylvania tomorrow morning, with heavy precipitation affecting western PA by the afternoon and late afternoon. The rain will run into the type of airmass mentioned above, which should lead to a mix of snow, sleet and freezing rain falling in central Pennsylvania. While the set up will not be as favorable in the area, the timing is the main question, as if the storm can arrive fast enough, by at least 11 AM-noon on Thursday, it could produce frozen precipitation as far east as the immediate north/west suburbs of NYC. The timing and the temperatures are likely to be favorable enough for at least a little snow/sleet to fall in the interior parts of the area.


Thursday Night - Friday: As the first rain band associated with the warm front lifts out of the area, warm air advection will take place, changing any leftover frozen precipitation in the Mid Atlantic to rain, with an occasional shower overnight and rising temperatures, which could reach the lower 50s in NYC. This band will move on to produce a wintry mix in other parts of the Northeast.

By Friday, the cold front should move through the area, producing a round of moderate rain in the morning into the early afternoon hours. Due to a strong cold air mass behind this cold front, it will be able to produce back end snow into Pennsylvania, and may lead to a few flakes in the interior parts of the area as temperatures start to drop in the afternoon. Meanwhile, a secondary low pressure will develop in New England, which will enhance the rainfall amounts in these areas.


Friday Night - Sunday: Much Colder
The coldest air mass of the fall so far will move into the area behind this storm, which is the leftovers of the current extreme cold spell in the northwestern and north central US, where low temperatures will drop below -20 degrees in the mountains. The GFS model, before trending to the currently expected scenario with the Thanksgiving storm, had a large source of cold air spilling into the Northeast, leading to very cold, if not near record temperatures. The storm, however, will block this source of cold air, leading to a cold air mass but not as extremely cold as modeled to be at first. High temperatures are likely to be in the upper 30s to mid 40s for the area on Saturday, with overnight lows ranging from the lower-mid 20s inland to the lower to potentially mid 30s in NYC.

By Sunday, the cold air mass will start to weaken, with slightly warmer temperatures, however another storm will start to organize over the Rockies, which may later on move into the Great Lakes, producing another round of brief warmth and rain for the area for early next week followed by another round of colder temperatures. Stay tuned for more information on this time frame.

Monday, November 22, 2010

November 22, 2010 Brief Update

Note: If you have read the winter outlook before this update was posted, please check the bottom of the winter outlook, as a small edit was added in.

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No full update will be posted tonight, the next one will come tomorrow, though below I will briefly review the expected scenario for the next week, which I will discuss in more details tomorrow as well as the longer range and an update for early December.


Tomorrow will be another mild day for the area, with highs in the upper 50s to mid 60s across most of the area, though a few showers are possible in the evening hours as a cold front comes through.

Wednesday should be much colder, with highs only in the 40s to lower 50s, with overnight lows even colder, in the 20s for most of the area except for NYC and the immediate coast.

On Thursday, while it no longer appears that the immediate NYC area has much of a chance of seeing front end snow out of the storm except for parts of Rockland county, the interior areas still have a chance of seeing some snow/sleet when the storm starts on Thursday afternoon, which will change over to rain in the overnight hours. There could be flakes for the central and western parts of the area on Friday evening as the cold front moves through and temperatures drop. More will be discussed on the Thanksgiving storm with tomorrow's update.

For the weekend, while extreme cold is not expected, slightly below average temperatures are likely, from the upper 30s to mid 40s across the area, with lows in the 20s for most of the area except for NYC and the immediate coast. Temperatures on Sunday will start to warm up as another storm may then form in the central US and potentially move towards the Great Lakes according to the latest models. Stay tuned for more details on this time frame.

Sunday, November 21, 2010

Final Winter 2010-2011 Outlook

Final Winter 2010-2011 Outlook
NYC Weather

Meteorological winter is only days away, and the pattern we are seeing now is already becoming a winter-like pattern, with several strong arctic air masses dropping into the Midwest, which will reach the area in a modified version after Thanksgiving. Winter 2009-2010 was a historic one for the Mid Atlantic, with over 80 inches of snow in the Washington DC area, the snowiest month on record in the NYC area, as well as a late February blizzard that brought NYC one of its biggest snowfalls on record.

Last winter, most signs pointed out to a cold and snowy winter in the Mid Atlantic, and there were even indications that the winter could be a historic one before the winter started. While this year’s winter outlook was a little more difficult to make, as there are more uncertainties than there were last year, signs are pointing towards a much less extreme winter in the northern Mid Atlantic, with snowfall ranging from slightly below to above average, with the cold and snow focusing further north and west, which I will discuss in more details below.


Part A: Factors For The Winter Outlook


La Niña:

So far in 2010, we've gone from a strong El Niño in the start of the year to a borderline strong La Niña in the fall. Such a rapid transition is not something that was common in the last 60 years, though it has happened before. Last winter's strong El Niño was different from most strong El Niños, which are typically east based and associated with a mild and dry northern US and a cold and wet south. Last winter had a west based El Niño, which combined with the right amount of cold and an active southern branch, led to historic snowfall in the Mid Atlantic.

This year's La Niña is also different than most strong La Niñas. While a typical strong La Niña would be west based, with a +NAO and -PNA pattern leading to a storm track through the Great Lakes/Midwest with a warm east and a cold west, such as the winter of 2007-08, this La Niña started out east based and is still east based, even though it may transition to more of a central/slightly west based La Niña later on in the winter.In addition, the NAO has generally been negative, when it would typically be positive with a strong La Niña. On average, an east based La Niña has less warmth and more cold in the east, with very cold temperature departures in the north central US.

The La Niña developed as an east based one in the summer and fluctuated between east and central based in the fall, however recently the La Niña became much more east based as the western ENSO regions saw weakening of the cold departures, which gives a high confidence level on this winter staring out with an east based La Niña. In my preliminary winter outlook, I expected the La Niña to be more central based by now, though this has failed to happen so far. Despite this, some La Niñas that started out as more east based became west based by the end of the winter, and while I do not think that this La Niña becomes a completely west based La Niña, I continue to expect gradual shifting to a central based, potentially slightly west based La Niña by the end of the winter. It is also possible that the La Niña simply stays east based through the whole winter, which could lead to slightly colder/snowier conditions in the East than I am expecting.

For the intensity of the La Niña, it has reached a peak earlier this month, and while La Niñas typically peak in the middle of the winter, it is possible that the La Niña may already have peaked. From the start, the models were showing this La Niña peaking unusually early, it’s now November and it appears that the La Niña either peaked in intensity or may peak in intensity within the next month, with weakening expected later in the winter.

NAO:

The North Atlantic Oscillation (NAO) is an important factor in addition to the La Niña. When the NAO is negative, it typically results in a colder East coast, and when it is positive, warmer temperatures generally take place in the East. On average, the NAO tends to be positive during La Niña winters. Last winter, we saw a strong -NAO which contributed to the unusually favorable set up of cold and snow in the Mid Atlantic. This year, we saw a consistently negative NAO, strong at times, which was one of the longest lasting -NAO periods in the last few decades. The La Niña is currently moderate, and we have been seeing a -PNA so far, which is also frequently associated with stronger La Niñas, however the NAO continues to be negative, with a strong -NAO expected for the end of November into early December. While a -NAO does not always mean that it will be cold in the East, as we are now seeing with a -NAO and a -PNA a southeast ridge is expected for early this week, but it won't be as strong as it could've been as the -NAO is preventing the SE ridge from becoming even stronger, which will be something that may repeat itself at times this winter.

For this forecast, I am expecting a generally negative NAO to continue through December into potentially early-mid January with an occasional period of +NAO possible, with a more variable NAO from January into parts of February where +NAO periods could become more frequent, but with –NAO periods also expected.

PNA:

The Pacific/North American Pattern (PNA) is also an important factor in the general pattern across the US. When the PNA is positive, that means there is a ridge in the western US resulting in above average temperatures, and can sometimes mean a trough in the eastern US resulting in below average temperatures. When the PNA is negative, a trough is likely for the western US with below average temperatures, which can mean a ridge in the eastern US bringing above average temperatures. So far this month, we have been seeing a –PNA in place, which led to cold conditions in the west and north central US. Despite the NAO being negative, the –PNA and –AO which have produced and will likely continue to produce strong arctic air blasts into the north central and NW US have occasionally led to a ridge in the eastern United States. This ridge would typically be a strong one with a +NAO, however since we are seeing a –NAO, this ridge is weak compared to what it could have been.

At this time, the models are expecting a trend towards a neutral PNA by early December, leading to an increased potential of cold and snow in the Mid Atlantic/Northeast. For this forecast, I am expecting a variable PNA through most of December into early January, which can range from negative to neutral with occasional positive periods, with an occasional +PNA possible in the second half of the winter but with a –PNA more common.


Other Factors:


It has been observed that sometimes, colder than average Octobers result in colder than average winters for Central Park, NY and Philadelphia, PA. 2009’s October was slightly colder than average and resulted in an average winter. 2007’s October had record warmth and the following winter was unusually warm. October 2010 brought below average temperatures, and the following winter brought near-slightly below average temperatures to the Mid Atlantic. This October ended up with slightly above average temperatures, which could support a slightly warmer than average winter.

The SE ridge is something that is usually seen with La Niñas, especially strong La Niñas. The SE ridge is a high pressure off the East Coast, which tends to bring above average temperatures to the SE US, or if it’s strong enough, to all of the eastern US. We have already seen the SE ridge appear from time to time this month due to a –PNA keeping the cold further west, however it was unable to become strong due to a persistent –NAO. While I think that the NAO will be slightly positive at times, I am expecting a generally neutral to occasionally slightly negative NAO, meaning that I’m expecting the SE ridge to generally be weak when it does appear, though there could be a few periods of time where the SE ridge becomes strong, combined with a +NAO, especially in parts of January and February. There will also likely be some times where we see a –NAO/–AO and a strong cold spell can briefly push into the Mid Atlantic and/or parts of the SE, but such strong cold spells likely won’t be too common, with most of the intense cold spells focused in the north central US.


Part B: Forecast For The Mid Atlantic


As previously mentioned, a –NAO, -AO and neutral PNA pattern is expected to start December, which may lead to a favorable time frame for cold and snow in the Northeast and potentially the Mid Atlantic for the first week of December. The pattern in December will likely be a variable one with periods of cold and snow, however the pattern will mainly depend on the PNA, as when the PNA is negative, the cold will be focused further west, with milder conditions for the East and an inland storm track, and when the PNA is more neutral, there should be more cold/snow periods affecting the region, especially the northern parts of the Mid Atlantic. The storm tracks could range from a few coastal lows to mainly inland tracks, Alberta clippers, and a storm track through the Great Lakes or Northeast with a Miller B low, or redevelopment near or off the Mid Atlantic/NE coast. For December, I am expecting slightly below average temperatures with occasional periods of slightly above average temperatures, with near to slightly below average snowfall for the southern Mid Atlantic and slightly above average snowfall for the northern Mid Atlantic.

December patterns:
Variable PNA, negative to slightly positive
Negative NAO


January could be a more variable month, though it appears that especially by the second half of January, we could see a transition to a pattern a little more similar to that of a typical La Niña, with a more negative PNA, and the AO/NAO still slightly negative but with more periods of slightly +NAO possible. The SE Ridge should appear more frequently in this month, and could also be briefly strong at times. As a result, I am expecting slightly above average temperatures further north and above average temperatures further south, with slightly below to below average snowfall.

January patterns:
Negative to occasionally neutral PNA
Slightly negative – slightly positive NAO


February is not expected to be a cold and snowy month at this time, though there should be differences from January. I am expecting the pattern to become more active in February, and based on analogs from most La Niñas, above average precipitation could be a good possibility from the central/northern Mid Atlantic into the Northeast and further west. The SE ridge could be weaker in February than in January, with colder temperatures returning to the NE US, which combined with the colder temperatures could lead to increased snow in the Northeast and snow/mix events in the central/northern Mid Atlantic. While the main storm track should be inland, there should also be snowfall from Alberta clippers, overrunning events, and Miller B storms that are inland first then redevelop off the coast of the Mid Atlantic. At this time, I am expecting slightly above average temperatures and snowfall slightly below average in the south and near average in the north, though the forecast departures for February have less confidence than those of the earlier months.

February Patterns:
Neutral-slightly negative NAO
Negative-neutral PNA


Winter Summary:


Overall, this winter should be less extreme than last winter, but near to slightly above average snowfall is possible in the northern Mid Atlantic, with near-slightly below average snowfall in the central Mid Atlantic and slightly below to below average snowfall in the southern Mid Atlantic. The average storm track should be inland, in the Northeast and Great Lakes, though a few storms may be coastals or move into the Midwest, with other tracks including Alberta clippers, overrunning events, and Miller Bs that are inland storms which redevelop off the Mid Atlantic coast. There should be more mixing with sleet and freezing rain than last year.


Part C: Forecast For The Rest Of The US


Western US: As the storm track moves through the NW US, expect above average precipitation in the Pacific Northwest, with a wetter winter than last year. With colder than average temperatures also likely, expect above average snowfall.

California will see a much drier winter compared to last year, and while some rainstorms are still possible, most of the storms as well as the storm track will be focused to the north, with near average temperatures and below average precipitation likely.

Midwest: (Minnesota, N/S Dakota, Montana): Expect below to well average temperatures this winter, as strong cold air masses dropping from Canada will focus on this region. Precipitation is expected to be near to slightly above average, with snowfall also slightly above average.

Great Lakes: As the storm track will focus on the Great Lakes and Northeast, this will likely be an active region this winter. Above average precipitation is expected for most of the Great Lakes, and as the storm track is expected to be close to the region with colder air to the west, below average temperatures are also likely, but not as cold as those in the Midwest. While there could be a few times where the SE ridge could be strong enough that the storm track is near the Great Lakes/Midwest and some places see rain/mix, there will likely be a lot of snow in this region, with above average snow likely, especially in the second half of the winter.

Southeast: December could be more of an average month, but as the SE ridge develops, warmer than normal temperatures and drier than average conditions are likely to develop and persist for a good part of the winter. There will be a few times when strong yet brief cold spells could make it down to the SE along with some snow, but this will likely not be too frequent. Above average temperatures and below average snowfall is expected.


Experimental forecast snow totals by city:


New York City
December: -1 to -3 degrees
January: +1 to +3 degrees
February: 0 to +2 degrees
Overall: -1 to +2 degrees
Snowfall: 20-32 inches (Average: 26 inches)

Philadelphia, PA
December: -1 to -3 degrees
January: +1 to +3 degrees
February: 0 to +2 degrees
Overall: 0 to +2 degrees
Snowfall: 15-25 inches (Average: 19 inches)

Washington DC
December: -1 to -3 degrees
January: +2 to +4 degrees
February: 0 to +2 degrees
Overall: +1 to +3 degrees
Snowfall: 9-16 inches (Average: 16 inches)


Part D: US Winter Maps









**Note:** As this is a long range outlook, there are some uncertainties on the exact patterns for each month. If necessary, a separate monthly outlook will be posted for each month as it gets closer.


Edit On November 22:

While I did not mention it in the winter outlook when it was posted, the pattern is expected to turn more favorable for more cold and snow in the Northeast by the second half of February, which may reach the northern Mid Atlantic. Depending on the La Nina and the pattern, it is possible that March could end up being a colder and potentially snowy month for the Northeast and even parts of the Mid Atlantic.

As said in the note above though, there are uncertainties on the exact patterns as this is a general long range outlook, and a separate monthly outlook will be issued as March gets closer.

**Notice**

3:07 PM (Nov 21): The winter outlook will be posted late tonight, with an update about the Thanksgiving storm before the winter outlook possible tonight before the winter outlook. Also, check the latest 5-Day Forecast, which includes a special update on the Thanksgiving storm.

Saturday, November 20, 2010

Nov 20, 2010: Uncertainty With Long Range

**Notes: The 5-Day Forecast was also updated for the interior tonight, with updates in the 5-Day Forecast in Long Island/S CT to be resumed soon.

The winter outlook is currently being made revisions to, and is expected to be posted tomorrow instead of the regular daily discussion.


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Today was a partly cloudy and breezy day with warmer temperatures, reaching the mid 50s inland, mid to upper 50s in the immediate NYC area and in the lower to mid 50s in Long Island/S CT. A weak cold front moved through earlier today, and a colder air mass is now entering the area. While the coming week should start off mild, a storm is expected for Thanksgiving day, with a cold and windy weekend to follow.


Tomorrow's Outlook:

Tomorrow will be a partly sunny day, with high temperatures colder than those of Friday, in the lower to mid 40s for most of the area, except for the immediate coast and the immediate NYC area which should be in the mid to potentially upper 40s. A NE turning SE wind is expected during the day.


Monday - Tuesday: Very Mild

A low pressure in the Midwest on Sunday night is expected to start pushing out the cold air mass, leading to a ridge building in the East on Monday. High temperatures are expected to reach the mid 50s to lower 60s across the area, with the warmest temperatures in the warmer spots in the immediate NYC area.

Overnight, as another low pressure organizes itself over the Midwest, a cold front should move through the Ohio Valley producing rain and thunderstorms, with a mild air mass persisting over the area leading to mild overnight lows, in the mid to upper 40s inland and upper 40s to lower 50s in the immediate NYC area. The cold front will weaken by the time that it moves through the area on Tuesday evening/night, though it will still be capable of producing light rain showers, with high temperatures on Tuesday in the lower to mid 60s for most of the area and mid to upper 60s in the immediate NYC area, making it the second warmest, if not the warmest day of the month.


Wednesday - Friday: Thanksgiving Storm, But Uncertainty Continues

On Wednesday, as the cold front from the earlier storm moves through the area, temperatures will cool down into the upper 40s to mid 50s across the area, but the cold air mass will not be able to advance much further southeast due to another developing storm.

Model Trends: As yesterday's discussion mentioned, the GFS model was too progressive with the storm, already bringing rain to the area by Wednesday afternoon, which is a typical bias of the GFS, and it developed the wrong low pressure, leading to a mess of weak, disorganized and suppressed low pressures. The GFS is now backing away from these errors, and is developing a low pressure further west and has the whole storm slower, taking it into the Great Lakes like the other models have been doing for the last few days. Afterwards, however, it has significant differences with what to do next with the low, with some runs absorbing it into a larger low near Newfoundland to forming a Miller B low pressure off the New England/northern Mid Atlantic coast leading to a larger storm in the Northeast. The ECMWF and GGEM continue to be even more west, even putting the storm in the Midwest. This could be too far west, and I would expect these models to trend back east over the next few days.

Forecast: While there is uncertainty on the development of the storm, some things are likely, such as rain falling in the area from Thursday in the morning/early afternoon hours into Friday, the general storm track being in the Great Lakes/Ohio Valley moving east/ENE, not NE like a typical storm in that area, and there is also the potential for Miller B, or coastal redevelopment off the New England coast. As there is too much uncertainty at this time and given that this is still in the medium range, I am not going to go into more details into the specifics of the storm, but I am expecing rain for Thursday into Friday with potentially moderate rainfall amounts. Stay tuned for more details on this storm and how it may affect the area.


Saturday/Sunday: Cold, Windy

Despite differences with the storm, there is higher confidence for the weekend. It will get colder behind the storm, but the models have backed off from the intensity of the cold. The previous GFS runs from yesterday were way too cold, and showed what would be well below average temperatures, with highs in the lower to mid 30s and highs in the upper 10s to mid 20s. The GFS model has trended more conservative, showing high temperatures in the mid 30s to lower 40s and lows in the lower to upper 20s. While there is uncertainty on how cold it gets, below average temperatures are expected.

Windy conditions are likely on Saturday and potentially Sunday given the stronger storm to the NE of the region, and if the GFS solution was to verify, strong winds could be possible, however there is still too much uncertainty to know for sure what happens, as some models are still showing the coastal solution with snow to its north, the ECMWF barely shows a cold spell, and the GFS simply has cold moving into the region. This time frame will be discussed in more details once the scenario becomes clearer.

Friday, November 19, 2010

Nov 19, 2010: Looking At Thanksgiving, Beyond

Note: The 2010-2011 final winter outlook will be completed soon, and is likely to be posted on Sunday. The polls for this winter's temperatures and snowfall departures in NYC remain open for the next week, please vote if you have not done so yet.

- The 5-Day Forecast was updated for the immediate NYC area only, though an update tomorrow morning or afternoon will add the rest of the area.


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Today was a mostly sunny day for the area, and temperatures were colder than yesterday as a trough moved into the area, with high temperatures in the mid 40s inland, upper 40s to lower 50s in NYC, mid to upper 40s north and west of NYC, and in the mid to upper 40s in Long Island/S CT.

Tonight's temperatures are already colder than expected in some places, as a result I have slightly lowered the forecast low temperatures. Tomorrow will be warmer than today with colder temperatures for Sunday, followed by a mild start to next week. Afterwards, however, a storm is expected around Thanksgiving, which could be followed by very cold temperatures for this time of the year.


Tomorrow's Outlook:

Tomorrow will be a mostly sunny day with a SW wind changing directions towards west. High temperatures are expected to be in the lower to mid 50s inland, mid to upper 50s in the immediate NYC area, and in the mid 50s for Long Island/S CT.

Looking at the rest of the region, a weak low pressure will be moving through northern Maine with snow, which should also bring a cold front through the area. The air mass, however, will be directed from west to east, meaning that it will not dig south, leading to a boundary setting up near the area separating the cold and mild temperatures.


Saturday Night - Sunday: Cold Again

On Saturday night, as the cold front will be to the east of the area, low temperatures will likely be cold again, even a little colder than tonight, reaching the mid to potentially lower 20s inland, mid 20s to lower 30s north and west of NYC, and in the mid 30s for NYC and closer to the coast.

Sunday should be another cold day, with high temperatures similar to those of today, if not slightly colder, in the lower to mid 40s inland, in the N/W suburbs of NYC, and in southern CT, mid 40s in Long Island, and mid to upper 40s in NYC. Cloud cover is expected to start increasing on Sunday afternoon.


Monday - Wednesday: Mild Start To Week, 60s Briefly Return

Monday will be a warmer day for the area as a low pressure in the Great Lakes starts to push the trough out of the region, while a high pressure starts to spread towards the SE US, leading to a SW wind. High temperatures will be in the lower to upper 50s across the area, with overnight low temperatures mild for this time of the year, only reaching the lower 50s in NYC.

On Tuesday, a high pressure of the SE coast should lead to a ridge extending through parts of the eastern US, however the strong -NAO in place will prevent this from becoming a large warm spell, and this will be something important to observe as it may apply to some cases this winter. Meanwhile, to the northwest of another storm developing in the Great Lakes, a strong polar air mass will drop into Montana and the Dakotas, bringing sub-zero high temperatures and lows even below -10 degrees Fahrenheit. This cold air mass will need to be watched as it will be an important factor for the weekend.

In the area, high temperatures will rise into the upper 50s to mid 60s, with a cold front from the storm in the Great Lakes bringing a cold front into PA, which should bring light rain to the area on Tuesday afternoon into the early overnight hours.

Wednesday should be a colder day after the cold front moves through, with some light rain possible, however the cold air mass will not be able to advance much further south/east as another developing low pressure sets the stage for a storm during Thanksgiving.


Thanksgiving Outlook: Some Uncertainty, But Storm Expected

The models for this time frame have been consistent with showing a storm, but there are differences with the intensity and the location of the storm. The GFS, typically having a weak and progressive bias, has a weak low pressure in the northern Mid Atlantic producing light rainfall, while the other models, even the GFS Ensembles are showing a much stronger storm further inland, like my discussions mentioned over the last 2 days. The GFS also seems to be too fast with the storm development, showing it further east than the other models on Wednesday, another reason why it may not have the right idea yet. Given the GFS' bias and its typical performance with storms in this time range, and the expected pattern of some ridging near the East Coast and a strong trough in the north central US, I continue to expect an inland storm track similar to the ECMWF/GGEM in some ways.

On Wednesday in the late afternoon, a low pressure is expected to start approaching the Ohio Valley moving ENE. While the exact track is still uncertain, the low pressure could then start turning more northeast and intensifying, likely being near the Great Lakes on Thursday. This storm, however, won't be a pure Great Lakes track, as it appears that with the pattern in place and what the models are suggesting, the storm may transfer its energy to a coastal low off the coast of New England. The storm will then exit by Thursday night, bringing a cold front through with a much colder air mass behind it (more on that below).

At this time, I am expecting rain for the area during Thanksgiving, with temperatures generally near average. Behind the storm, the air mass will be much colder, and if there is enough precipitation present, snow flurries may fall into Friday. This storm could be a strong one, with impacts ranging from heavy snow to the north/west of the storm given the cold air mass and the potential for windy conditions after the storm passes through. Stay tuned for more details on this storm and how it may affect the area.


Friday-Sunday: Very Cold Temperatures Possible

As previously mentioned, a strong polar air mass will drop into the north central US on Tuesday. This cold air mass will start advanding east, being west of the Thanksgiving storm by Thursday, and once the cold front moves through, the strong cold air mass will likely be able to drop into the area, bringing 850 mb temperatures near or even slightly below -10c. If this solution verifies, high temperatures could be as low as the 30s in most of the area, with low temperatures in the 20s and even 10s inland.

There is still some slight uncertainty with what happens in this time frame, and the GFS runs and some of its ensemble members have been showing another low pressure developing to the south of this trough, moving ENE and potentially bringing frozen precipitation into the Mid Atlantic. While this solution still has a lot of uncertainty given that it's mainly showing up on the
GFS, it will be watched in case it does become more likely. Stay tuned for more details on this time frame.

Thursday, November 18, 2010

Nov 18, 2010: Stormy And Colder Thanksgiving Potential

Note: The 5-Day Forecast was updated for the immediate NYC area only.

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Today started out as a mostly sunny day but clouds increased later on in the day, with high temperatures peaking in the mid 50s inland, mid to upper 50s in the immediate NYC area, and in the mid 50s for Long Island/S CT. An isolated shower was reported across parts of the area, but for the main part no more than a trace of rain was recorded.

Tomorrow will turn much colder for the area, with Saturday slightly warming up and Sunday cold again, with temperatures warming up for early next week. Afterwards, however, indications are that the pattern could get stormier, leading to a potentially stormy Thanksgiving day, then cold Thanksgiving weekend.


Tomorrow's Outlook:

Mostly sunny skies are expected for the area tomorrow, along with a north wind turning west. As a colder air mass reaches the area, with 850 mb temperatures near -6c, temperatures will be much colder tomorrow, with highs in the lower to mid 40s inland, mid to potentially upper 40s in Long Island/S CT, and in the mid to upper 40s for the immediate NYC area.

Looking across the rest of the Mid Atlantic and Northeast, cold temperatures will be in control, with high temperatures in central/northern Maine below freezing. Places such as Virginia will see highs in the mid 50s.


Weekend Outlook: Warmer Saturday, Cold Sunday

On Saturday, a weak low pressure in southern Canada will move into Maine, leading to light snow in that area, with the storm pushing out the trough and briefly bringing a warmer air mass. This will lead to high temperatures in the lower to mid 50s inland and in the mid to upper 50s for the rest of the area with a SW wind expected.

The storm's cold front will then push through for Saturday night, bringing a much colder air mass into the Northeast with the area in the bondary of the cold temperatures of the north and warmer temperatures to the south. Overnight temperatures on Saturday night should be very cold, in the lower to mid 20s inland, mid 20s to lower 30s for the north/west suburbs of NYC and southern CT, and mid to upper 30s in NYC.

Sunday will be another cold day for the area, especially further north, with high temperatures in the lower to mid 40s inland and in the mid to upper 40s for the rest of the area.


Monday - Wednesday: Mild Start To The Week

On Sunday night, a weak low pressure in the Midwest moving northeast into Canada will push the cold air out of the region, with a high pressure near Maine moving towards the Southeast coast. As a result, Monday will be warmer for the area, with high temperatures generally in the mid to upper 50s with a SW wind expected. Meanwhile, a low pressure will be organizing close to where the first one will on Sunday, and will move NE.

On Tuesday, a high pressure is expected off the SE coast, however with a -NAO, this will be blocked from becoming a widespread warm spell. A cold front related to the second storm will approach the area, bringing a risk of showers into Tuesday night. Meanwhile, a strong polar air mass will be dropping into the Midwest, bringing sub-zero temperatures to those areas, and a low pressure could form near Colorado that may be the makings of the next storm to affect the area.

The cold front will bring colder temperatures into the area for Wednesday, however the cold air mass will not be able to advance much further east due to the next developing system.


Thanksgiving Weekend: Stormy, Then Much Colder

As mentioned over the last several days, there is the potential for a storm to affect the region during Thanksgiving day, potentially lasting into Friday. Yesterday, some models hinted at strong suppression and snow potential, however this seemed unlikely, and the models are now showing an inland track. Given that this is in the longer range, there are likely to be some changes, but with a generally warm SE and a strong cold air mass in the north central US, I am thinking at this time that this storm could track inland, somewhere near the Great Lakes or the Northeast, pulling in a warmer air mass into the area for Thursday or Friday depending on the timing. The models are also hinting at the storm making an energy transfer to a low off the New England coast, and this potential will be watched.

Whether the west or east track verifies, this storm could be a potentially strong one, with large impacts, including thunderstorms and potentially severe weather to the south of the storm, strong winds, and potentially heavy snow to the northwest of the storm. Behind the storm, the strong cold air mass could be directed at the region, and with a strong -NAO and a moderating -PNA, there is the potential for much colder temperatures to affect the area during the weekend. Stay tuned for more details on this time frame.

Wednesday, November 17, 2010

Nov 17, 2010: Colder Weekend, Next Week Starts Mild

Today was a mostly cloudy and windy day for the area, with high temperatures peaking early in the morning in the lower to mid 60s across most of the area. There were some heavy showers and thunderstorms last night, however the storms in the Mid Atlantic into parts of New Jersey and Pennsylvania were stronger than expected, and produced wind damage. The rest of the day was windy across the area, and the wind is expected to weaken later tonight.

After another day of comfortable temperatures, a chilly weekend is expected for the area with warmer temperatures for next week, however this will be the start of a stormier and colder pattern that may set up for Thanksgiving weekend.


Tomorrow's Outlook:

Tomorrow will start out with mostly sunny skies but with increasing clouds later in the day across the area with a west wind expected. High temperatures will be in the mid to upper 50s inland, mid to upper 50s in Long Island/S CT, and in the upper 50s in the immediate NYC area. An isolated shower is possible in the late afternoon in the western parts of the area.

The leftover precipitation and cloud cover from a weak storm that is expected to dissipate tomorrow will reach the area tomorrow night, which will lead to mainly cloudy skies and the potential of an isolated shower. With 850 mb temperatures could enough and surface temperatures in the 30s, a few snow showers could fall north and west of NYC.


Friday - Sunday: Chilly

On Friday, the colder 850 mb temperatures will be over the area, which will lead to chilly conditions. High temperatures will be in the lower to mid 40s inland, mid to upper 40s for the immediate NYC area, and mid to upper 40s in Long Island/S CT.

For Saturday, the cold air mass will briefly lift out of the area with slightly warmer temperatures, however a weak low pressure will be moving through Maine, bringing light snow into these areas, and an even colder air mass will follow behind this storm. The air mass, however, won't be able to dig far south, and will generally move east, if not slightly ESE, with a boundary setting up near the area with chilly temperatures to the north and warmer temperatures to the south. As a result, Sunday's high temperatures are likely to be similar to those of Friday, with low temperatures for Sunday morning a little colder than those of tomorrow night, in the 20s away from the immediate coast, and lows in the lower 20s are possible inland.


Monday - Tuesday: Warming Up

On Monday, a low pressure moving through the Great Lakes will pull the trough out of the Northeast, with a high pressure moving towards the SE US, leading to warmer temperatures with a SW wind developing. 850 mb temperatures will start to warm up as the SE ridge builds itself, however the main thing preventing this from being a large spell of above average temperatures is the negative NAO, which will block the ridge from extending too far north, leaving the area with at least slightly above average temperature.

By Tuesday, a strong polar air mass will be dropping into Montana and the Dakotas, and with the SE ridge persisting, a storm is expected in between, near the Great Lakes, with its cold front slowly pushing east. Temperatures on Tuesday will be the warmest of this time frame, potentially in the lower to mid 60s in the immediate NYC area.


Thanksgiving Weekend: Colder, Stormier?

Afterwards, uncertainty increases as there are differences with the models, however there are two main solutions at this time. The first is that the cold front slowly moves eastward, with weak waves of low pressures developing along the front, until a stronger storm will form and pull in the cold air mass into the region, leading to a cold Thanksgiving weekend. Another possible scenario is that the cold quickly moves into the Northeast for Wednesday, then moves out as the next storm develops, leading to an inland storm track for Thanksgiving weekend, which is shown by the 06z GFS and 12z ECMWF, which still bring in the colder air behind the storm.

While there are large differences, what is known at this time is that there will likely be a large cold air mass in the north central US, at least a weak southeast ridge, and there could be a storm around November 25-27, and while it is still too early to determine the exact track, my first thoughts on the potential track given the set up and the pattern is a potential track between the Mid Atlantic and the Great Lakes, though this could change as details become clearer. With plenty of cold air available, snow could fall to the north of the storm. Stay tuned for more details on this time frame and any storm potential for Thanksgiving weekend.

Tuesday, November 16, 2010

Nov 16, 2010 Noon: Rain Entering

10:00 PM: No full update will be posted tonight, though for the main part the forecast is mainly the same as it was yesterday. Either tomorrow or on Thursday, expect a new detailed discussion on the coming pattern.

In addition, the final 2010-2011 winter outlook will be posted either late this week or in the coming weekend. Stay tuned!

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9:10 PM: Moderate to heavy rain is currently starting to fall in the immediate NYC area as expected from this afternoon, due to an area of moderate to heavy rain. Radar estimates show this area of rain dropping an additional 1/2 inch over most of the places it affected, and even though it has weakened, it will still be capable of producing 1/4 to 1/2 inch of rain with amounts potentially slightly higher in the areas of the heaviest rain, which should be in the immediate NYC area and potentially parts of Long Island. A rumble of thunder is also possible with the rain.

Once this round of rain ends, drier conditions will take place for the next several hours with occasional showers and rising temperatures, however the storm will not be over yet, as the cold front with the storms currently in western Pennsylvania/Virginia will move into the area, producing more heavy rain and thunderstorms later tonight.

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5:15 PM: An intensifying storm that is currently moving northeast into Ohio from Kentucky has started to bring some light rain to the area. Some rain from this morning was associated with a different area of rain, though the rain this afternoon is associated with this storm as the northern edge of the rain continues to push north.

While the area is currently dry, a line of moderate rain in the central Mid Atlantic is moving northeast, and should bring another round of rain for the area this evening. Temperatures will remain steady in the area during the evening, and by at least 10 PM-12 AM, should start rising as the cold front approaches. Heavy rain and thunderstorms are expected to fall in parts of the overnight hours as temperatures rise, peaking in the mid to upper 50s inland and in Long Island/S CT and upper 50s to lower 60s for the immediate NYC area. The rain should end by tomorrow in the late morning hours as windy conditions develop.


The next update will be posted later tonight, with more information about the longer range.