Dec 22, 2010: Sunday-Monday Snowstorm Potential

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

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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.