New York City Metro Weather

Snow before Halloween??

Posted by: NYCvort, 8:43 PM GMT on October 27, 2011

The first real cold air mass of the season will be filtering in behind a cold front today and tonight. Frost advisories are in place for many of the suburbs with freeze warnings over the interior. This will set the stage for an interesting weather scenario unfolding for the weekend. A strong shortwave diving down across the northern Plains will phase with southern stream energy tomorrow. As this energy rounds the trough and takes on a slight negative tilt by early Saturday, cyclogenesis will occur off the mid-Atlantic coast with a strengthening low pressure system expected to take a track up off the coast near the benchmark. Right now the main global models including the GFS, ECMWF, and GGEM all support such a scenario. The NAM is still well offshore, but doesn’t follow the general model consensus with regards to orientation and sharpness of the trough axis. For that reason I am disregarding it. With plenty of cold air aloft, this would almost certainly lead to a significant snowstorm for the I-95 corridor had such a scenario occurred two months from now. However, instead we will have some significant boundary layer issues considering time of year. Interestingly enough, sun angle will not be a problem as this would be the equivalent of early-mid February, but still the low levels remain very warm.

Temperatures at the onset will be too warm to support anything but rain, even after evaporative cooling lowers the air temperature somewhat. However, dynamic cooling of the layer as a sub-546mb trough pushes overhead will likely cause the rain to mix with snow late Saturday and possibly change over to snow briefly before ending. This changeover would occur earlier for interior sections and latest at the coast. Take a look at the potent negative tilt trough moving overhead late Saturday:

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About NYCvort

I am a native New Yorker who has been studying and forecasting the local NYC weather for years. I especially enjoy tracking winter storms.

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