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Posted at 01:16 PM ET, 04/11/2012

Snow and sleet reported in Washington, D.C. metro region: what’s going on?


Jet stream configuration on April 11, 2012 compared to March 23 (Unisys Weather)
It’s raw and cold outside and we’ve been receiving reports of rain showers and yes - sleet, graupel and snow - in some areas mainly from the District and to the north and west. Accumulating snow has even fallen in the Laurel Highlands of Pennsylvania and in western Maryland. It’s neither completely surprising, nor unprecedented.


Satellite image shows bubbly clouds - produce mixed precipitation, reflecting cold air aloft and atmospheric instability (NASA)
The setup: the airmass is unseasonably cold and a disturbance is passing by.

The jet stream has taken a huge dip over the Eastern U.S. allowing Arctic air to pour south. It’s in almost exactly the opposite configuration as March, when we had record-breaking warmth.

At the same time, an upper level disturbance is zipping through the region. When you mix together the the strong April sun, the unseasonably cold air in the atmosphere, and the energy associated with this disturbance, the end result is a lot of atmospheric instability. The result? Showery precipitation - and where it’s cold enough - of wintry forms.

These popcorn-like showers are mostly producing rain, but north and west of the beltway, there’s enough elevation and cold air in place for some of the precipitation to mix with sleet and snow and/or form graupel. Even though surface temperatures are in the 40s, the air higher up in the atmosphere is sufficiently cold enough for frozen precipitation.

These showers will remain possible through around sunset.

Reports/photos from readers...

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Snow in April can and does happen

Ian Livingston wrote two years ago: “Snow has accumulated during April in Washington, D.C. 20 times since authentic records began at the start of 1888”

The latest accumulating snow on record occurred on April 28, 1898 (0.5”). The last time 1” fell in D.C. during April was April 1, 1924.

Latest inch+ of snow on record

D.C.: Apr 12, 2.0 1918

Baltimore: Apr 11, 2.0 1894

Dulles: Apr 12, 1.0 1973

Latest measurable snow on record

D.C. Apr 28, 0.5 1898

Baltimore: Apr 28, 0.1 1898

Dulles: Apr 12, 1.0 1973

Related links

Is April snow in D.C. becoming more rare?

April Weather: Both Appalling and Amazing

What is Washington, D.C.’s weather like in April? Breaking down norms and extremes

By  |  01:16 PM ET, 04/11/2012

 
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