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.

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