From the ABC 7 Weather team

Wintry Mix Possible Friday. Slippery PM Commute?

February 20, 2013 - 08:14 PM
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A powerful winter storm impacting the Central US could bring the dreaded "wintry mix" to D.C. just in time for Friday's evening commute.

A powerful winter storm is taking shape in the Central U.S. and will impact us, in D.C., by weeks end.  The storm system is originating in the Desert Southwest and has already brought snow to parts of Arizona, including Tucson and Phoenix.  Much of the Plains and Midwest already under either winter storm warnings (pink), winter weather advisories (purple), or winter weather watches (blue). 

The center of the storm system will track North through the Plains and into the upper Midwest through Friday.  Notice, in the image below, the area of low pressure over Chicago.  Also, notice the warm front (red) through the Carolina's and the pink (ice) that extends North of that front.

As the warm front lifts North through the day, Friday, light precipitation will accompany the front, especially out ahead of the front.  I want to emphasize "light" since some of the latest trends are showing much less moisture associated with the warm front, which would be a good thing, especially since the precipitation could fall as the dreaded "wintry mix". 

Check out forecast temperatures at 4pm Friday.  I grabbed a wide shot to show the cold air over the MidAtlantic, but to also show the milder temperatures in Kentucky and Ohio.  Those will be areas south of the warm front by Friday afternoon.  Temperatures at 4pm around the metro area will be in the mid to upper 30s.

Penn State e-wall Hi-Res NAM 18z

Temperatures will be around freezing, but mainly above the freezing mark, so that would rule out freezing rain in D.C. with any precipitation around that time.  Temperatures aloft, or higher in the atmosphere, will be around or above freezing, so that's why there's the concern for freezing rain and/or sleet.  Here's a great link to help explain the process of snow, sleet, and freezing rain

As mentioned before, the amount of moisture associated with the warm front continues to be less and less with the newest guidance, but certainly something we'll want to monitor.  If the precipitation would fall around the evening commute, which it looks like the likely timing, as of now, then that could certainly cause some travel problems.  Temperatures through Friday night and very early Saturday morning will be close to freezing, so the ice concern will stick around through the period, especially with more moisture moving in overnight Friday.

By Saturday mid morning, temperatures will be above freezing throughout the atmospheric profile, so a chilly rain in store for Saturday.  Another area of low pressure will develop over the Southeast and become more organized, as it moves up the coast. 

18z GFS
A rainy Saturday for D.C., but maybe more snow for New England come Sunday, as the same low intensifies off the New England coast. 

As always, we'll watch the developing systems and keep you updated with any new information!

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