** Winter storm watch Wednesday night and Thursday **

A major winter storm is expected in the region Wednesday night and Thursday, with heavy snow accumulations possible – though not guaranteed. Our current forecast calls for 5-14 inches across the area, with the highest amounts in our western suburbs.

Capital Weather Gang snowfall forecast, issued noon, Tuesday, 2/11.

The forecast remains complex, but let’s lay out some basics:

  • No weather problems tonight and during the day tomorrow.  Just cold, with lows 12-20 degrees tonight, and highs near 32 Wednesday, with increasing clouds.
  • The start time for snow is most likely between 7 and 10 p.m. Wednesday night
  • Snow may fall heavily at times Wednesday night into early Thursday morning and, with a cold ground and subfreezing temperatures, it will stick.  We are fairly confident in at least several inches of snow by dawn Thursday for much of the metro area.  Hazardous driving conditions are likely
  • Uncertainty creeps into the forecast during the day Thursday, when warmer air might be drawn into the storm, changing to snow to sleet and rain, especially for areas along and east of I-95.  Areas that remain all or mostly snow – most likely  from western Fairfax and western Montgomery and to the west – are most likely to receive 8 or more inches of snow. Inside the Beltway and points and east, how much snow accumulation occurs during the day Thursday versus sleet versus rain is a huge wild card.

Models: The NAM model continues to advertise all snow for the region, including areas along and east of I-95, and double digit totals.  The GFS model – just in – is more in line with the other models.  It indicates snow to start but, for areas near and east of I-95, a changeover to mixed precipitation Thursday morning.

GFS model simulation shows rain/snow/mix line close over D.C. at 7 a.m. Thursday. (WeatherBell.com)
GFS model simulation shows rain/snow/mix line close over D.C. at 7 a.m. Thursday. (WeatherBell.com)

Maryland State of Emergency: Given the forecast Maryland governor Martin O’Malley has issued a State of Emergency Declaration. It will “will allow the state to deploy members of the Maryland National Guard, allow emergency contracting by the Department of General Services and waive certain rules and regulations to speed recovery from the storms” according to the release from the Maryland Emergency Management Agency.

Thundersnow?: In analyzing the latest NAM model, CWG’s winter weather expert Wes Junker identified a potentially unstable layer in its representation of the atmosphere which may be favorable for thundersnow if its simulation plays out.  Something to keep an eye on.


Programming note: This update takes the place of the usual PM Update published around this time.  We’ll be live-blogging the models as they come in this evening, starting around 9 p.m.