First Snow of the Season for Many

2013111118_metars_dtw

It’s not hard to find the front on this afternoon’s weather map. A sharp wind shift moving through central Michigan and Chicago northeast into eastern Ontario and southern Quebec is plowing south. The coldest air of the season lurks behind the front. You can also see a number of locations reporting snow particularly along the Illinois/Wisconsin border.

gfsNE_sfc_prec_021

The front will approach Connecticut Tuesday morning before daybreak and with it will come a band of rain and snow. The question is how quickly will temperatures drop behind the front (how fast rain will change to snow) and how much precipitation falls.

Here’s a sounding from the NAM valid tomorrow morning in Hartford before daybreak. There’s a few things to note here that I’ve annotated.

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The presence of “relatively” strong upward motion in the snow growth zone (where the atmosphere is between -12 and -18C) and the fact that there is a fairly deep layer of saturation argues for efficient snow growth in the clouds. That’s a plus for snow. The one issue to note is that, at least initially, it’s too warm near the ground for snow in the valleys and the shoreline. Rain or a rain/snow mix would be possible. In the hills this would be an all snow sounding.

SREF total QPF plumes for BDL

SREF total QPF plumes for BDL

There won’t be a lot of moisture or precipitation. Models are generally showing around 0.1″ of QPF. Given that some will fall as rain and some snow won’t accumulate we are talking about snow amounts that will be quite marginal. A coating to an inch of snow is possible in some towns while other towns may see flakes in the air but will wind up with just a trace of accumulation.

Models do show heavier amounts of precipitation (up to 0.2″) in southeastern Connecticut so with an offshore wind and rapid cold advection it’s possible even the shoreline manages to squeeze out a coating of snow as slightly warmer temperatures are offset by more precipitation falling.

While this won’t be a significant event it will come during the height of the morning commute and in many towns temperatures will fall from near 40º to below freezing as the rain changes to snow. This will lead to some slick travel!

NAM 2 meter temperatures at 1 p.m. Tuesday

NAM 2 meter temperatures at 1 p.m. Tuesday

Regardless of how much snow falls (or doesn’t fall) tomorrow will be a cold day. Temperatures will be in the 30s during the day and it will be breezy. At least for a day it will feel like winter has returned!

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2 thoughts on “First Snow of the Season for Many

  1. That is one heck of a skew-T presentation? Can ordinary folk get access to that?

    I did wonder what that white line of “upward motion” actually is a measure of. Can you explain? Or anybody else? Is anybody listening? Not a lot of response on this site. N

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