GFS: Early October Snowstorm?
By Quincy Vagell on October 2, 2012, 1:50pm
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The above GFS forecast image of snow has been all over social media today.
Could it really be, snow coating the ground in the NW hills of CT and over a half foot of snow near the Capital District of NY?
Breaking it down:
Accumulated snowfall maps can be a bit deceiving. They often only account for temperatures above the ground, near about 850mb. While that is all well and good, if the air temperature a few hundred feet above the ground is above freezing, it becomes much harder for snow to accumulate.
(also keep in mind a lot of these maps assume the ground is 32F and that the liquid to snowfall ratio is 10:1)
Early season storms:
2011 was a great example of why early season snow storms are possible, but EVERYTHING has to go the right way.
As a general rule, you want the atmosphere to be cooler than normal and you need a deep sub-freezing layer, especially from about 925mb to at least 850mb. This is because the snow flakes won't have to overcome warm boundary layer temperatures.
In the case of October 2011, even though the SURFACE was above freezing, the air above the ground was abnormally cold. This was thanks to an intense area of low pressure.
Look at the temperatures from 850 to 925mb and near the surface...
With warm temperatures in the boundary layer, snow will NOT accumulate!
Always take these early season snow "accumulation" maps with a grain of salt. Not to mention that a lot can change in five days.
Forecast:
Some chilly rain is certainly possible. Hey, the higher elevations of interior New York and even the mountains of VT/MA could possibly see a touch of wet snow mix in. However, the odds of anyone near us seeing 7 inches of snow this early in the season, given the forecast setup is just about impossible.
Keep in mind the models don't show a deep nor'easter like 2011. A storm like that can manufacture some of its own cold air.
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