Breaking down tonight’s snow shower chance in the D.C. area


Only very light amounts of precipitation are simulated by the models overnight into tomorrow morning, and mainly east of I-95

A minor upper level weather disturbance drops through the Mid-Atlantic region tonight and tomorrow morning, offering the opportunity for a few rain and snow showers. Little or no snow accumulation is expected.

This is a classic clipper-type disturbance with very limited moisture as it’s riding along the jet stream from the northwest.


NAM model shows a healthy amount of upper level energy (or vorticity) cycling through the region

The best chance for rain and snow shower activity – as simulated by weather models – is generally east of I-95 – as a very weak wave of low pressure tries to spin up near the coast, tapping a bit of Atlantic moisture.


The GFS model suggests a weak wave of low pressure may develop along the coast, perhaps injecting a bit of moisture into the otherwise dry upper level disturbance passing by, mainly east of the District

Here’s how I see this “event” unfolding:

* After 8 p.m., hit-or-miss showers enter the region from the west (30 percent chance of precipitation). They may briefly begin as rain with temperatures around 40, but with plentiful cold air at high altitudes – change over to snow with temperatures falling back into the 30s.

* Between 11 p.m. and 5 a.m., scattered snow showers are possible throughout the region, with the highest chances (around 40 percent) east of I-95 and lowest chances towards in western areas (20 percent).

* Between 5 a.m. and 10 a.m., there’s a 20 percent chance of a few lingering flurries west of I-95, with snow showers ending east of I-95 (30 percent chance).

* Snow accumulation odds: 20 percent chance of a coating or so west of I-95, 40 percent chance of a coating to 1 inch east of I-95. Little or no snow accumulation is the most likely outcome everywhere.  Temperatures near and slightly above freezing limit any minor accumulations to car tops and grassy areas for the most part.

* All in all, expect this to be a low to no impact event in the region.  Flakes should mainly be “conversational” in nature.

Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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Dan Stillman · March 20, 2013

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