UPDATE:  The NWS seems to be backpedaling a bit on its snow forecast this afternoon. Meteorologists are now calling for 1-2 inches across northern Maryland, and only an inch south of Baltimore. The storm track appears to be turning more northward, through PA, which will invite drier air to push into our region sooner rather than later, cutting off the snow. Another inch could fall during rush hour. Earlier post below.    

Forecasters believe Maryland counties north and west of I-95 are likely to see more snow than Southern Maryland as the track of the approaching Alberta Clipper begins to emerge from successive runs of the forecast computers.

The NWS has issued Winter Weather Advisories until 10 a.m. Friday from Allegany County to Harford County, including Baltimore County and City, Howard and Montgomery counties. From Baltimore south, including Prince George's County, there is only Hazardous Weather Outlook, suggesting less snow and less disruptive conditions south of Baltimore.

That's pretty typical of these Alberta Clipper storms. They're relatively dry; they move quickly, and their snow trail is pretty narrowly focused.

The forecast for Baltimore calls for 1 to 3 inches of light, fluffy snow tonight, beginning mostly after 10 p.m. as temperatures drop into the mid-20s. The snow will continue into the morning rush hour, with another inch or so possible before it ends.

Here's AccuWeather.com's snow forecast map.

Here's Mr. Foot's forecast. He seems to be leaning toward a prediction that schools - at least in the northern counties - will close or delay: 

"It is highly probable many school systems affected by this snowfall may be delayed or closed. Snow will be falling at the crucial decision time of 4 to 5 AM. Were a large school system to announce a delay at 5:00 AM, there is only a 2 hour window delay during which a re-examination of conditions can occur. The 850 mb data clearly shows that by 7 am on Friday, the final shortwave now in Mississippi will not have cleared the region.

"Stormcasters and Student Collaborators are monitoring this system closely because it contains vigorous energy that will feature high liquid-to-snow ratios due to very cold air at upper levels. Will it be another case of "storms from the west don't bring extra rest?"  Tonight, prudent teachers and students will no doubt still do the right thing and get homework and lesson planning completed as usual." 

The snow will end quickly as the storm moves on toward New England, stopping first in the southern counties as the storm draws dry air - the "dry slot" - into the southern and eastern range of its center.

Behind it we'll see temperatures drop and winds accelerate, forecasters say. The weekend looks sunny but cold, in the 20s - that's 15 to 20 degrees below the average for this time of year- with overnight lows in the teens. Wind chills will be in single digits.

Out in Garrett County, where it has been snowing all week (21 inches this week at Wisp) , they're expecting another 7 to 11 inches from the clipper tonight. And the upslope, lake-effect snows will resume after the clipper passes by. Wind chills will fall to between 5 and 10 degrees below zero Saturday night. 

For the record, forecasters at Sterling are already mentioning another clipper-type storm for Tuesday of next week.