There will be no rest for the snow-weary in Maryland as a storm with the potential to drop 10 to 20 inches of new snow bears down on a region still reeling from the 24 inches and more that fell over the weekend.
The National Weather Service issued Winter Storm Warnings on Monday for all of Maryland west of the Chesapeake Bay, calling for light snow to begin mid- to late afternoon today. Forecasters said it should intensify early Wednesday morning as colder air moves into the region, and continue throughout the day.
If this storm tops 20 inches at Baltimore-Washington International Thurgood Marshall Airport, it would be the third such pummeling this season, a trifecta unprecedented in Maryland weather history.
"I think we're all awed by it," said meteorologist Matthew Kamar, a forecaster at the weather service's Baltimore-Washington Forecast Office in Sterling.
It also seems sure to set a new seasonal snowfall record for Baltimore. The old record is 62.5 inches, set in 1995-96. The total for this winter stood at 60.4 inches as the storm approached.
"I hope, with the weight of the additional stuff, it doesn't cause too many problems," said James E. Lee, meteorologist-in-charge at Sterling. "But there is a point where some structures are going to succumb to the heavy weight."
Then there's the big melt.
"Sooner or later we're going to be talking about flooding on the Potomac and flooding on the Susquehanna. I hope we just get a nice, even warm-up and not a real strong blast," Lee said.
There may be a little good news in the forecast. While the new storm will start with the sort of wet, heavy snow shovelers dread, once the cold air arrives early Wednesday the flakes will become fluffier, lighter and easier to move when the digging and plowing begins anew late Wednesday and Thursday.
The bad news is that lighter, fluffier snow piles up faster, which is why the predictions range as high as 20 inches. Or maybe higher.
The student forecast team at FootsForecast.org, which predicted the weekend storm would deliver 25.6 inches of snow at BWI-Marshall Airport (within an inch of the 24.8 inches the weather service estimates fell there), is expecting lots of snow this time, too.
"The forecast team ... told me the number they're looking at is about 1.6 inches of liquid," a measure of how much water would fall if the storm delivered all rain, said Rich Foot, the Baltimore County physical sciences teacher who heads the group.
"So we're thinking if you just go by the rule of 10 to 1 [inches of snow for each inch of liquid water in the storm], that could be roughly 16 inches of snow.
"Our concern with the cold air that's in place now [is] the ratio won't be 10 to 1. The ratio may be closer to 16 to 1. And that's a number I'd rather not calculate, because I just don't think our area could take that right now."
Do the math anyway, and you get more than 25 inches of snow.
Kamar said the complex storm system headed this way is unusual in that its most potent piece is a pair of lows coming from the west, rather than up the coast. Usually, the coastal storms are the worst for Maryland.
As the western lows merge, intensify and head this way, a new, weaker, secondary low is forecast to form off the coast of Florida and Georgia, and move up the coast toward Delmarva.
"Some light snow will develop Tuesday morning to early Tuesday afternoon for the Baltimore area," Kamar said. That snow will look much like the light snow on Friday, which fooled some into thinking the weekend storm would be a dud.
The coastal low will even draw some warm air into the mix. "So we're going to see maybe a transition across Southern Maryland to include some sleet and even some rain Tuesday night," Kamar said. "Where that [line between rain and snow] sets up exactly is a matter of detail we probably won't be able to define until the system is nearer."
But then the low moving out of the Plains states will begin to introduce much colder air into the mid-Atlantic. It may even produce a brief end to the wet snow during the night. But it's not the end of the snow.
The colder air will also introduce instability, triggering more intense snowfall. "So we would expect to see some [intense] snow bands set up," Kamar said, "and that looks to happen over Northern and Central Maryland southeast to the D.C. suburbs, and especially Baltimore and portions of Southern Maryland as well. That's where we expect the heaviest snow to be.
"When people wake up, they're very likely to see moderate to heavy snow," he said, perhaps at rates of 1 to 2 inches an hour. "The snow may continue through most of the afternoon into the early evening" before the storm departs.
Extreme Western Maryland will likely see more lake-effect snows later in the week. But east of the mountains we appear headed for a series of cold, but sunny to mostly sunny, days through the weekend.
Lee said he expects the measurement of this storm at BWI will be done according to National Weather Service protocol.
Errors by a private contractor paid by the Federal Aviation Administration to make weather observations at the airport during the storm led to questions about the reliability of the measurements.
The contractor was supposed to make a measurement after six hours, wipe the snow board clean and repeat the process every six hours until the snow ended.
Instead, the snow was measured hourly, with a total of 28.8 inches, Lee said. Another measurement at the end of the storm, after the snow had compacted, gave a total of 24.8 inches. The weather service used the more conservative 24.8 inches, still the second-biggest two-day snowstorm in Baltimore's history. And the number will stand, Lee said.
"We're done with it," he said.
What's on the way
The National Weather Service issued a winter storm warning from noon today to 7 p.m. Wednesday with snow accumulations of 10-20 inches. Foot's Forecast predicts snowfall of 12 inches across Central Maryland, with some areas exceeding 20 inches.
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