Jan 21, 2011: Significant Storm Potential Wednesday


***This post is from 2011. Please visit the MAIN PAGE to see the latest forecasts for January 2012.

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The snowstorm that affected the area early today ended by the late morning, with partly to mostly cloudy skies and scattered snow showers observed for the rest of the day. Snow totals were generally between 2 and 6 inches across the area, however the storm did bring heavier snow totals as it moved northeast into the rest of southern New England and Maine.

Behind this storm, what may be the coldest air mass of the winter is moving into the region, and is expected to bring low temperatures in the single digits for Sunday night across most of the area with sub-zero lows inland. While the cold pattern will not end afterwards, as indications are showing that it may last into February, the main focus at this time is on a potentially significant or major storm for Wednesday that will affect the region.

Saturday – Monday: Extreme Cold

Tonight will be very cold for the area, with low temperatures expected to be in the lower to mid 0s inland, mid 0s to lower 10s for the north/west suburbs of NYC and S CT, with mid 10s in NYC. Tomorrow will be a partly sunny day but with temperatures much colder than those of today, in the upper 10s inland and in the upper 10s to to mid 20s for the rest of the area.

The cold will relax a little on Saturday night as a weak low pressure to the north of the area brings mostly cloudy skies and scattered flurries, with low temperatures still cold but not as cold as those of tonight. On Sunday, high temperatures will be in the lower to mid 20s across the area with clearing skies, though the second and strongest part of the cold spell will move in.

Sunday night is expected to be very cold, with low temperatures near or below zero degrees for most of the area away from NYC and Long Island. Low temperatures may even get as low as nearly -10 degrees for the westernmost parts of the area, and an Extreme Cold Alert may be issued there. Even New York City may see low temperatures in the single digits.Monday will then be a very cold day, with high temperatures in the mid to upper 10s across the area, with a few isolated areas near NYC potentially reaching the 20 degree mark.

Monday night will still be very cold, especially for the eastern and central parts of the area, where low temperatures near zero degrees in southern Connecticut are possible. While there is plenty of more cold air to come, the attention for now turns to a major storm for Wednesday.

Tuesday – Thursday: Significant Storm Expected, Uncertainty With Precip Type

As I mentioned this morning, there is now agreement with the forecast models that a significant storm is expected for Tuesday into Thursday. The main question at this time, however, is how the storm affects the area, as it appears that this storm may track close enough to the area to bring a wintry mix during Wednesday.

Model Analysis: Other than most models showing an intense storm, the smaller details including the track, intensity and timing are different which can be expected in this time range. The GGEM model has one of the westernmost solutions at this time, with some front end snow changing to heavy rain and temperatures well into the 40s, The ECMWF was in between with what appears to be a wintry mix for the area, and the GFS has been more variable, showing a snow to rain storm with its 06z run and a major snowstorm with its 12z and 18z runs.

The pattern in this case is not as favorable for a major snowstorm focusing on the area as some other storms were, including a lack of blocking and a high pressure that exits quickly, and at this time a blend of the more reliable model runs seems to take the storm right up the coast, with a major snowstorm further inland into places such as Pennsylvania, and a wintry mix for places further east including the Interstate 95 corridor. A snow storm is still a possibility for the area though, as it is possible that a faster solution like that of the GFS verifies and brings a moderate or heavy snowstorm for the area. For my forecast tonight, I used the 12z ECMWF and the 06z GFS, though this is still subject to change over the next few days. It is possible that we may see the eastern, faster and weaker solutions of the GFS verify, and it is also possible that we may see a storm further west, closer to the GGEM.

Current Thoughts For NYC Area: At this time, it is certain that the storm will affect the region as well as the NYC area. I went a little conservative and put a 90% chance of precipitation at this time, though if there are no major changes I will likely raise it to 100% with tomorrow’s update. As we will see a very cold air mass exiting ahead of the storm, with cold air in place to start, the storm is expected to start out as snow across the area, though what happens afterwards becomes more uncertain and depends on what the storm does.

There are timing differences concerning when the storm starts and ends, with solutions ranging from the snow entering during the day on Tuesday to the storm only starting on Wednesday afternoon. At this time, I went with the in between solutions, showing snow starting on Tuesday night, though with uncertainty concerning the timing, this is subject to change. During the day on Wednesday, when the storm may make its closest approach to the area, if the western solutions verify, it will track close enough to NYC to change the precipitation type to rain with a wintry mix further west, but if the storm is east enough, it may keep most of the area with plain snow. It is also possible that we see a weaker storm in which the area sees more of a moderate snow event. In the 5-Day Forecast, I leaned towards the western solutions, showing snow changing over to a mix or rain for NYC and a snow/mix further west, though this is still subject to change.

It is important to note that we are still 5 days away from the storm, and we may see solutions ranging from a big storm bringing some snow to rain, to a storm bringing a major snowstorm to the area, to a weaker storm with lighter snow for the area. While I am leaning more towards the western solutions at this time, the other scenarios are just as possible and cannot be ruled out. Stay tuned for more information on this storm over the next several days.

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