Without beginning another post, this will just be an update on our present situation. Overall, I like my ongoing forecast--a very tough one at that--and my thoughts are outlined below:

For the Immediate metro region (including DC, Baltimore and points south and east to St. Mary's and Calvert Counties)

DCweather Snowstorm Timeline

7AM-10AM: Snow/sleet/freezing rain mix begins to fall
10AM-2PM: Wintry precip rapidly begins to turn over to rain as warmer air moves into the area
2PM-8AM (Fri): Rain continues to fall, heavy at times, and should melt any ice that accrued to surfaces during the morning

Storm Impact: School Forecast: (**AM Travel conditions may be a bit hazardous as ice/snow accumulates on roads/sidewalks/etc.**)

PREVIOUS DISCUSSION
Today through Wednesday:
As high pressure parked to our north in southern Canada continues to strengthen, stiff Northerly winds will funnel much colder air into the region, and high temperatures will struggle to eclipse the freezing point this afternoon-evening under mainly sunny skies. On top of this, winds gusting 10 or 15 mph are adding salt to the wound, dipping wind chills into the mid and upper teens!

Tonight will be another brutally cold period as clear skies and calm winds allow what surface warmth snuck down to the surface to radiate back into the atmosphere. Low temperatures in the far western 'burbs may fall into the lower teens (definitely some single-digits out towards Johnstown, PA), and into the mid to upper teens closer to the metro region.

Not much changes in this cold weather pattern for Wednesday--and the only noticeable difference may be a few more high level clouds streaming in from the west in association with a developing low situated in the Upper Midwest. High temperatures tomorrow will also be around 30-34 degrees.

Thoughts on Thursday's "Snowstorm"
There currently remain very minor differences between computer models regarding this week's potential wintry weather bonanza. High pressure to the north will be our supply source for cold surface temperatures, and a significant moisture train from the Gulf of Mexico will be our source for precipitation. I like the idea that precipitation breaks out across the metro region early Thursday morning in the form of snow showers. However, a tongue of warmer temperatures aloft should begin melting any snow as it falls through the layer between 1000 and 3000 feet up. Surface temperatures will likely remain below freezing through the mid morning, which would support some freezing rain/sleet which would likely begin accruing to any sub-32 degree surfaces.

The problem I am having revolves around when (and if) precip switches over to rain by noon Thursday. The NWS in Sterling seems to think most of the precip would remain a wintry variety, which would cause some significant travel problems and school cancellations around the region. Basic Climatology, however, tells me otherwise.

This early in the season, we can't really expect surface temperatures to remain below freezing with easterly surface winds, and warming mid levels. I do not presently believe this next wintry blast will cause too many problems around the immediate metro region. The wintry mix should turn over to a cold rain from DC south and east by noon, limiting problems around the metro (although there may be some travel hazards during the morning hours while snow and freezing rain falls).

Out to the north and west, things get a little dicy. Surface temps would likely support frozen precip through most of the day, and significant ice accumulations are possible north of Loudon-Montgomery-Frederick counties.
Potential Storm Impact:
-Travel problems possible during morning hours
near DC, significant icing possible northwestern MD

Above image: Schematic of a freezing rain environment (similar to that of a sleet environment) as snowflakes melt in a shallow warm layer aloft before refreezing closer to the surface as sub-freezing raindrops. These accrue to roads, telephone lines, trees, etc. causing significant problems for the affected regions