Forecast Mostly On Track

As it has looked from the beginning, this is going to be an issue of temperatures and whether the intensity of the storm and the dynamic cooling processes in the atmosphere can overcome the marginal cold air and the complete lack of a strong cold air source.

This storm and the forecasts around it have high bust potential.

Still - climatology and atmospheric analysis suggests that the DC metro area and especially points west and north have a good chance to end a 2-year snow drought in spectacular fashion.

The NAM model run from this morning is one of the more bullish solutions for this storm.  Here is the clown map it rendered from the morning run:

Now the NAM does have a precipitation bias - it can overdo the precipitation forecast.  Still, if this were to verify, it suggests widespread totals of a foot or more in DC and especially westward where totals could exceed 15 inches.

The GFS is slightly less excited but still shows our region in the bullseye of the storm:

Although as you can see, the gradient of precipitation is quite tight on the eastern side and the snowfall amounts drop off rapidly as you go east.

Track is often the most important thing with winter storms but in this case, the track is almost the entire story.  There's not much question about precipitation falling tonight, tomorrow and tomorrow night.  The question is, "what type?"

A small shift - and we're talking maybe 50 miles - southward and this becomes a snowstorm with 10-15 inches of snow even inside the Beltway.  The same shift northward dramatically decreases the snowfall totals in the region and pushes everything west.

My sense is that snow will fall and accumulate and that we'll end the 2-year snow drought tonight and tomorrow.  But I do worry about the rain/snow line and how far westward it will move.  I also worry about how much precipitation will fall before it changes to snow.

Like I said:  high bust potential.

Right now, it seems reasonable to go with this forecast:

Tonight:  Precipitation begins as rain, probably in the evening, 5-6 PM is a good guess for the immediate DC metro.  Earlier to the west, of course.  The rain should fairly quickly start to mix with snow.  Overnight, closer to midnight, the rain/snow mix will changeover to all snow and the precipitation rates really get going.  If everything works out, we could see 2 or 3 inches on the ground by the time we wake up in the morning.

Tomorrow:  Snow for most of us but more mixing issues will be in store the further east you go in the region.  Out in Loudoun I expect they stay all snow but there probably be mixing issues east of the city.  The precipitation will be heavy both in the "intensity" sense and the "weight" sense.  This will be a wet snow which, combined with the expected winds, could cause power outages. 

Tomorrow Night:  Snow continues but starts to end from west to east overnight.  Only the far northeast suburbs should see any lingering light snow Thursday morning.

This NWS map seems reasonable at this time:

I'll update if anything changes!