Rain tops 1" in Baltimore; more coming
Lots on the weather docket this morning. First the rain we've already received. Baltimore and a number of other locations in Maryland have recorded well over an inch of rain in the last 24 hours as a major seasonal change in the large-scale weather patterns takes hold.
As autumn settles in this week, we will erase the shortfall in moisture we built up during the first three weeks of September. The forecast from the National Weather Service forecast office in Sterling projects as much as an inch and a quarter of additional rain through Tuesday. And, if things work out the way some models suggest, we could be looking at a great deal more rain before the month ends on Thursday as a tropical system moves our way.
First, the totals for the last 24 hours. BWI-Marshall is reporting just a little over an inch since the rain began Sunday morning. We have 1.06 inches on the gauge here at The Baltimore Sun. But here is a sampling of some higher numbers from across the region, from the CoCoRaHS Network.
Bowie: 1.68 inches
Bishopville, Worcester Co.: 1.63 inches
Baltimore City: 1.54 inches
Delmar: 1.52 inches
Pasadena: 1.38 inches
Kingsville: 1.29 inches
Towson: 1.01 inches
Ellicott City: 0.90 inch
Havre de Grace: 0.70 inch
Next, forecasters say we're looking at a "slight risk" for severe thunderstorms this afternoon and tonight along the I-95 corridor. "Heavy rain and strong gusty winds" are also a risk early Tuesday, forecasters said.
Here's why: There is a cold front parked along the coastal states, with low pressure centered over Georgia. The counter-clockwise spin around the low is drawing a load of moisture north out of the Gulf of Mexico and the Atlantic. Hence, our soaking rain, which is going to continue off and on through Tuesday as the low moves north into the eastern Great Lakes.
If enough warm air gets north along with the tropical moisture, that could trigger thunderstorms in the area as the cold front approaches the region. Flash flood watches are already posted to our south and west, in parts of southwest Virginia, but not yet for us. It's been so dry, there is plenty of room in area streams to absorb much of this rain.
The NWS has issued a Coastal Flood Advisory for minor to moderate flooding on the Western Shore from Harford to St. Mary's counties at high tide as the low approaches and east winds drive bay water onto low-lying spots.
And as the cold front moves through early Tuesday, we may see another round of thunderstorms, heavy rain and gusty winds in the Baltimore-Washington corridor, forecasters say. An "isolated tornado" is also possible.
High pressure behind the cold front could clear skies later on Tuesday, and bring us some sunshine on Wednesday. But a tropical storm, or remnants of a storm, are forecast to be moving up the coast by Thursday. Models disagree on where the rain will fall.
Eric the Red, a professional meteorologist from Baltimore and a frequent contributer here, said the Canadian forecast model brings the storm along a more westerly track. That, he says, "would give the region a period of torrential rainfall Thursday and Thursday night."
"If I had to make an early call," he said, "I say we get smacked by either the remnants of a tropical storm, or the storm itself, during the latter half of the week ... The rain, while quite unpleasant to drive in, is much-needed ... and should put a dent in the developing/expanding drought in the region."
UPDATE: At noon, Eric adds this:
"The WRF/NAM [model] has between 3" and 7" of rain falling between now and Thursday night, and this does NOT include the tropical storm (should it stay close enough to the coast). Short-range model ensembles have similar results. Make sure those sump pumps are working and drains are clear of debris!"
(REUTERS PHOTO: Steve Schaefer, Sept. 26, 2010)