Slow movement by a pair of winter weather systems is expected to skid the start of today's snowstorm smack into Baltimore's evening rush hour.
The snow is likely to start falling here between 4 p.m. and 6 p.m., forecasters said early this morning.
"That's why we issued the watch as early as we have, so folks are aware, and plan now for the possibility," said Howard Silverman, meteorologist at the National Weather Service's Baltimore- Washington Forecast Office in Sterling, Va.
Commuters could catch a break if they're out of town early. "The bulk of the snow will actually be during the nighttime hours," he said.
The Winter Storm Watch posted Monday for the region means there's a potential for 5 inches of snow or more in parts of Central Maryland. The forecast for BWI-Marshall calls for 2 inches to 4 inches overnight, with more to the north and east.
Lesser amounts are likely farther west and south. "For the tip of Southern Maryland … there could be a little sleet or rain mixing in, which would cut down accumulations," Silverman said. "For D.C. and points west, snowfall amounts will taper down quite a bit."
It'll be cold, too, 5 degrees to 10 degrees below average for the rest of the week. Baltimore health officials declared a Code Blue Health Alert for Tuesday and Wednesday, proving extended hours for the city's emergency shelters. Outreach workers will check on vulnerable residents.
Heavier snows were forecast for cities up the Interstate 95 corridor, with 4 inches to 8 inches possible in Philadelphia, and 6 to 12 forecast for New York City, and southern New England.
Garrett County was also under a Winter Storm Watch, with 6 inches or more predicted there.
The wintry weather is the result of a complex pattern that is moving one storm system from the South and up the coast off Cape Hatteras, N.C., while another comes out of the Ohio Valley, passes to our north, and merges its energy with the coastal storm over the Atlantic.
That leaves much of Maryland between the two, with less snow.
For Baltimore, the latest storm comes after a series of bobs and feints by the winter's previous weather-makers.
On Dec. 10, motorists and highway crews were expecting flurries. Instead, vigorous snow showers made area roads unexpectedly slick. The icing caused scores of accidents and delayed afternoon school buses.
Another light snowfall on Dec. 16 dropped 1 inch to 3 inches across the region, and 1.2 inches at BWI-Marshall. But it closed schools early, coated roads and snarled evening rush hour traffic anyway.
There was a brief flurry of hope for a white Christmas, but that storm skirted the region. BWI recorded only a trace. Another dusting on Saturday added 0.3 inch to the season's total. But the tally remains an anemic 1.5 inches as the next storms gather. The average seasonal snowfall for Baltimore is 18 inches.
Could this storm fizzle?
"There is always a possibility," Silverman said. "But right now, with the Winter Storm Watch, the prudent thing to do would be to plan on the possibility of around, or greater than, 5 inches of snow."