UPDATE:
From what I can gather, a fairly sizeable storm looks likely for the DC metro region overnight tonight. Temperatures are hovering near the freezing mark, and will begin falling into the lower 20s after dusk. This storm is a fast mover and will likely only produce precipitation for 12 hours or so (if that). The heaviest precip moves into the area after Midnight, which will cause significant travel problems tomorrow morning.

***A WINTER STORM WARNING IS IN EFFECT FOR THE DC AND BALTIMORE REGIONS, A HEAVY SNOW WARNING FOR WESTERN MD, AND A WINTER WEATHER ADVISORY FOR LOWER SOUTHERN MD.***

An area of low pressure continues to intensify and organize over the Midwest, extending clouds, showers, and thunderstorms across the enter Southeast region.

High pressure dominating our weather today will back down from a confrontation with this low pressure center later today, as it weakens and moves eastward over the Atlantic Ocean. By 5AM, clouds and snow showers will have overtaken much of the region (including the District and BWI), and may become quite heavy before changing over to a mixture of sleet/freezing rain/snow over the immediate metro region.

Areas out west around Garret County, southwestern PA will likely remain all snow for the duration of this event and snowfall totals may exceed 10 inches in localized areas.

Closer to home, around DC, Montgomery county, and Baltimore, snow will change over to an icy mixture by late morning, and will compact snowfall totals significantly. Nonetheless, significant snowfall accumulation is anticipated in the said region: between 3 and 6 inches.

The Timing is Right for a Horrible Morning Commute:
As snowfall moves into the area overnight, during the coldest periods of the day, snow will likely begin accumulating shortly after it begins to fall. The morning commute around the region will be hazardous, and commuters are urged to use extra caution venturing out to work tomorrow.

And on this topic, timing is good for many school closings across the area.