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Monday, October 20, 2008

Frost vs. Freeze. First Snow in NY?

What is the difference?
A frost can develop with air temperatures as mild as 38F or 40F. It's the surface of your car, or blades of grass that can drop lower and allow condensing moisture to form ice crystals. A freeze however is when the air temperature actually drops to freezing (32F). The difference can lead to an abrupt end to the growing season for plants and late season crops. A hard freeze pretty much takes care of everything growing as temps drop below freezing for at least 4 hours. This morning, temperatures dropped into the 20s and 30s. That was the core of this cold spell and thanks to clear skies and Sunday's temps only reaching the upper 50s.

First Snow in NY
Beside my personal connection of 4 years in Cornell (Ithaca), working in Syracuse and Binghamton... I think it is worth mentioning the seasonal shift- even if it's not here.
Let's jump past the next cold front and into Wednesday morning. Here you can see the 850mb temperature map (the most efficient for measuring temperature forecasts).
Here you can the blue shading indicating colder air spilling in across the lakes. This is actually 6C-8C- which would translate to near freezing surface temperatures. No big deal, right? We just had that this morning. However, this profile of sub freezing temperatures near the Great Lakes- along with the proper wind flow, will allow bands of snow to develop.

Here is the surface weather map for Wednesday morning, showing a small and weak Low Pressure forming off of the New England Coast. That will enhance the North West flow across Lake Ontario and dump across central New York the first snow of the season. Considering the warm water temperature in contrast to the colder air, there could be some heavy bands of snow- but where will depend on the precise wind direction. I will focus more on this as the snow develops...but isn't that exciting? Not for us. The same northwest wind rides down the mountains and dries out. So this type of set up is not going to bring us snow. It's confined to the mountains and lee side of the lakes in NY. I'm jealous. First ski areas opening up in Colorado last week, and now snow on the way in my old stomping grounds. On a side note, Ithaca, NY had a Halloween snow storm in 1993 that dumped between 2 and 6 inches of snow. I don't find that a scary thought, but some of you may.

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