Sneaky Snow?

For people who love winter this weather pattern just plain sucks. Surprisingly, I haven’t been complaining about it. After October a break from winter has been nice – and it’s been nice for our heating bills too!

It appears that this may be one of the rare times that we are able to get a couple inches of snow to fall in a hostile early season weather pattern.

12z NAM / 48 Hours 500mb Vorticity & Height Forecast

Our computer models are showing a very powerful area of upper level energy ejecting from the southern Plains toward southern New England by Thursday. This vorticity maximum gets deamplified as it is crushed by a growing area of confluence over the Canadian Maritimes and the North Atlantic.

Occasionally this kind of setup can deliver what I like to call a drive-by snowstorm. A 6 hour window of snow in a somewhat localized swath. The storm will never become a powerful or mature cyclone as its upper level energy is zipping along and weakening. In addition in the mid levels of the atmosphere a low pressure system never really closes off and you’re left with an “open wave” effectively limiting the amount of precipitation that can fall.  See the 700mb NAM forecast to the left.

So what’s the bottom line? In a storm like this there’s little room for error. The storm has to “thread the needle” so to speak with a perfect track of the 500mb shortwave. At this point our models are in fairly good agreement with a track just to the south of Connecticut. With warm waters and a period of upper level divergence we should see a deepening surface low and a period of warm advection produce precipitation along and north of the shortwave’s path.

At this point things look cold enough for a rain/snow mix or snow as long as the storm maintains its current forecast track. Any adjustment north would back winds near the surface enough to warm the boundary layer and result in more rain especially for the valleys and shoreline.

The maximum amount of snow we can reasonably expect in a setup like this is around 6″ given an “ideal” track. Something less than ideal will result in less snow whether it’s due to mixing or due to the storm tracking too far south. Odds favor less than ideal but it’s worth watching.

By midday tomorrow we should have a better idea how this “drive-by” snow event will play out. It would be pretty incredible if such a mild meteorological autumn and beginning of winter was able to produce 2 plowable snowfalls before December 10. If you like snow don’t get too excited yet and if you don’t like snow don’t worry nothing is set in stone at this early juncture.

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6 thoughts on “Sneaky Snow?

  1. Forsythias are in blossom. Carnations and pansies too. Daffodils are coming up. A little snow won’t change the look. If this warm pattern returns for another 2-3 weeks, the chance of a cold winter diminishes substantially.

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