As a massive, slow-moving system is dropping 6-10 inches of snow across the region Thursday before ushering in more record-setting cold.
A winter storm warning remains in effect until 7 p.m., with snow showers expected to continue into the evening.
After the snow clears, frigid cold is forecast to set in. A wind chill advisory is in effect from midnight to 10 a.m. Friday. With overnight lows in the single digits, 5-10 mph winds are expected to make it feel like 5 degrees below zero to 15 degrees below zero.
By 3 p.m., snow totals included 10.5 inches near Manchester, 7 inches in Towson, 6.5 inches in Columbia, 6.3 inches in Baltimore's Pimlico neighborhood, 6 inches in Bel Air, 5 inches near Fort Meade and 4 inches in Pasadena, according to the National Weather Service.
Even before wintry precipitation arrived, most school districts in the region made decisions to cancel classes. Find the latest closings at bsun.md/snowday. Many government offices also closed.
Transportation officials meanwhile again dispatched plows and salt trucks across the region and warned drivers to avoid traveling during heavy snow. A fog warning is in effect on the Bay Bridge, and the National Weather Service warned that snowfall could reduce visibility to 1/4 mile or less.
Baltimore officials had to call on Montgomery County to bolster salt stores after they dropped to a quarter of what city Transportation Director William Johnson said he considered sufficient. As of Thursday, the city had 2,500 tons of salt on hand, even though Johnson said he likes to start major storms with closer to 10,000 tons.
"At this point, the priority is to make sure we have the resources," Johnson said.
The city was scheduled to begin Thursday evening receiving 7,000 tons of additional salt from Montgomery County under a mutual aid agreement between jurisdictions in the state, the cost of which would be "worked out later," Johnson said.
The city has already used 38,000 tons of salt this winter season, he said.
State Highway Administration officials urged drivers to stay off the roads during heavy snowfall. Crews did not pre-treat roadways with a brine solution that can prevent pavement from becoming snow-covered because it would have been washed away by rain Wednesday night.
"If you do choose to drive, be sure your vehicle can maneuver in the snow. Just one abandoned car can create a traffic jam that impacts everyone, including our plow trucks," said SHA Administrator Melinda B. Peters in a statement.
Baltimore City officials were gathering salt Wednesday after recent ice storms depleted stores, city Transportation Director William Johnson said.
"Traveling is going to be very difficult," Johnson said. "I would encourage all motorists to proceed with caution and plan your schedule accordingly."
City Health Commissioner Dr. Leana Wen declared a "Code Blue" advisory, opening up extra beds in homeless shelters Wednesday night, and the city also opened the War Memorial Building for use as a shelter through Thursday morning and again Thursday and Friday nights.
The number of deaths attributed to cold weather this winter has reached eight in Baltimore City and 31 across the state, according to a state health department report released Wednesday. The statewide total is more than twice the number of cold-related deaths reported last winter and one more than the 30 deaths reported in winter 2012-2013.
Meanwhile, firefighters are being called in to address thousands of water outages, frozen and burst pipes and water leaks that have occurred in the city amid cold weather. The city Department of Public Works is operating a 24-hour command center, implementing 16-hour shifts for maintenance workers and calling in contractors and other city agencies to help.
Public Works Director Rudolph S. Chow said Baltimore Fire Department employees will be using pumps to remove water from flooded basements, which can be caused by frozen sump pumps and broken water lines.
The storm affected a wide swath of the eastern United States before reaching the Mid-Atlantic. It is the result of plumes of moisture from the Gulf of Mexico moving across the southeastern United States to meet a strong cold front stretching from Texas to New England.
Winter storm warnings stretch from northern Texas along the Mississippi and Ohio valleys to the Mid-Atlantic, affecting some 57 million people, according to the weather service.
Unlike other major snowfalls caused by storms with powerful centers of low pressure, Thursday's precipitation is the result of a cold front moving its way into the relatively warmer air that moved over the region Wednesday. The cold air is wedging its way underneath the warm air, pushing it higher into the atmosphere where it cools and condenses to create precipitation, explained Mark Paquette, a meteorologist with AccuWeather.com.
"There's a rather narrow strip where precipitation is concentrated the most," Paquette said. "It's just about that clash of air masses."
It hasn't even been a year since Baltimore's last significant March snowfall — 8.1 inches fell on St. Patrick's Day and the preceding day. But if this storm can surpass that total, it could be Baltimore's biggest March snowstorm in two decades. A foot fell across the region in a March 1993 storm.
About 21 inches of snow have fallen this winter at BWI, about an inch above average.
After the snow ends, a spell of more unseasonably frigid temperatures is ahead. Lows are forecast in the teens and single digits Friday and Saturday mornings, with highs in the mid-20s Friday and upper 30s Saturday. Friday morning's low could break a record of 13 degrees that dates to 1901, while Saturday morning's cold could near a record low of 10 degrees set in 1960.
Temperatures approaching seasonable levels with highs in the low 50s could arrive next week.
Baltimore Sun reporters Yvonne Wenger and Kevin Rector contributed to this article.