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Posted at 11:38 PM ET, 10/28/2011

Light rain develops, snow in mountains

* Winter weather advisory for Fairfax, Montgomery, Prince William, Howard and southern Fauquier counties. *
* Winter storm warning for northern Fauquier, Loudoun and Frederick counties (and points north and west, including much of northern Md. and northwest Va.) Saturday - primarily above 1,000 feet *

* Accumulation map, storm timeline and frequent questions *

Patchy light rain has overspread the immediate metro region with temperatures generally in the low 40s (with some upper 30s in the north and west suburbs). Locations in west central Virginia above 1,000 feet or so, however, have been reporting snow. Overnight, low elevation rain and high elevation snow is likely to be the story. On Saturday, as the storm winds up and mixes in colder air, snow should gradually work down to lower elevations from west to east.

Refer to our forecast from earlier for details on what to expect, where and when. A few late evening notes before catching some sleep...

* So far this evening, I’ve seen reports of snow in Crozet, Va. (west of Charlottesville), Elkton, Va. (east of Harrisonburg), in Warren co., and at Wintergreen (ski resort in west central Va.). Temperatures and snow accumulation have depended on elevation, with generally a coating to 1/2” and temps 30-34 where it’s snowing.


Forecast snow accumulation through Sat evening. Forecast confidence: Low. Also, see storm timeline and FAQs
* The latest NAM model is fairly cold and wet suggesting some accumulating snow into D.C. and close-in suburbs, with substantial amounts in outlying north and west suburbs. This model is fairly skillful at this time range, so we have to keep in mind the possibility that snow could reach the high end of ranges shown in our accumulation map (or even exceed it in some spots). In addition, the NAM indicates the potential for convection and isolated thundersnow which could cause some big amounts somewhere.

* The GFS model which has simulated little or no snow in the immediate metro region in previous runs (and not much until you reach the mountains) has held court - indicating little if any snow in D.C.

* So which model is right? Climatology and the fact it’s late October supports the warmer GFS, but the NAM - while having a cold bias - typically better simulates low level temperatures. We continue to like a blend of the two - and our forecast amounts reflect that.

By  |  11:38 PM ET, 10/28/2011

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