Central and Southern Maryland should expect 3 to 5 inches of snow tonight, with the heaviest amounts close to the Chesapeake Bay, falling off to the west and south. Much of the Eastern Shore is being told to expect 1 to 3 inches, except along the Atlantic coast, where mixed precipitation will likely hold accumulations to little or none.

UPDATE, 10:45 a.m.: Baltimore, Howard and Harford county Schools will close an hour early Tuesday in anticipation of the snow. Anne Arundel and Kent schools will close two hours early. Here's the link. The National Weather Service has also updated its forecast snow map. The new one is now displayed below. It shows a much-diminished area of 4-5-inch accumulations (purple). Snow estimates in their Winter Weather Advisories have not changed.

The National Weather Service has issued Winter Weather Advisories for almost the entire state, calling for the snow to move in from the south and west. Forecasters believe it will begin snowing between 3 and 5 p.m. in Northern Virginia, Washington, D.C., Frederick, Montgomery and PG counties. Flakes should turn up between 4 and 6 p.m. east of there, including Westminster, Baltimore, Columbia and Annapolis.

Eric the Red, a professional forecaster from Baltimore, tells us the latest model runs suggest an earlier start for the snow:

"Latest radar, satellite, and model data has snow developing around midday, with an inch or so possible in the DC area during the eve rush, with lighter amounts in Baltimore due to a later start.  The period of heaviest snow will occur between 7 and 10 pm, and perhaps linger til midnight in nrn and northeast MD."

NWS forecasters expect temperatures to hold in the lower 30s, so the event is likely to remain all-snow. 

The fact that Sterling issued a Winter Weather Advisory rather than a Winter Storm Warning, means that they don't believe accumulations will top 5 inches in the Baltimore area. But their morning forecast discussion indicates their confidence in that conclusion is not ironclad:

"IT WOULDNT TAKE MUCH MORE TO RAISE THE BALTIMORE AREA INTO WINTER STORM WARNING CRITERIA. IF FRONTOGENETIC FORCING IS STRONGER AND DECENT BANDING OCCURS AND...OR IF PHASING [MERGER OF THE TWO STORM SYSTEMS] OCCURS SOONER...THEN HIGHER SNOWFALL TOTALS MAY RESULT. DO NOT HAVE ENOUGH CONFIDENCE IN THAT RIGHT
NOW...WHICH IS WHY ADVISORIES WERE MAINTAINED."

(I know the NWS map above is hard to see. Here's a link to the source page. Best I can do.)

Once the storm passes by, we won't be entirely out of the wintry weather. Colder-than-average temperatures and stiff winds will keep us in the icebox:

"WESTERLY/NORTHWESTERLY FLOW WILL QUICKLY INCREASE ACROSS THE AREA WEDNESDAY WITH GUSTS EASILY INTO THE 30 TO 35 MPH RANGE THROUGH THE DAY. WITH MAX TEMPS IN THE MID 30S...WIND CHILLS ARE EXPECTED TO BE IN THE TEENS IN THE MORNING AND NOT GET ABOVE THE MID 20S IN THE AFTERNOON." 

Elsewhere, the Northeast is bracing for the same storm, in spades. AccuWeather.com is saying Eastern Massachusetts could see 12 to 18 inches, with much of New Jersey and New York City due 6 to 12.

Here's how close we are to the Winter Storm Warning area, in purple, with 5 to 8 inches forecast in Philly, 4 to 6 in Dover.  

UPDATE  9 a.m.: Eric the Red has popped in, after a new look at the models. Something there has caught his eye:

"The off-cycle 06z run (1 am) of the WRF/NAM has changed its story dramatically.  It has the coastal low intensifiying faster and farther south, and is now upping the total to a half inch of liquid or more.  This would be at least 5" of snow, with higher totals across north-central and northeastern MD. 

"I am not ready to jump on this just yet, cos the same cycle run of the GFS has actually backed off.  But early morning visible satellite imagery is a wee bit disturbing, and radar shows the pcp [precipitation] breaking out sooner than expected.  I will keep you posted."

UPDATE: 10:45 a.m.: "Seeing another set of model data has set the record straight.  Last night's "uh oh" fcst from the WRF was just a blip, and it has gone back to the idea of 2-4" for most of the region.  There may be higher totals in northeastern MD, but most areas are looking at a quick shot of 2 to 4 inches.  I suspect DC may come in a tad lower, with 1-3".