Central Maryland is in for a gusher of rain overnight and throughout the day Thursday as a potent storm system moves out of the Gulf states with a heavy load of Gulf and Atlantic moisture.
On top of rainfall that could total 3 inches before the storm ends Friday morning, forecasters said persistent winds from the east and southeast will pile up high tides on the bay Thursday, two to three feet above normal.
The National Weather Service Wednesday posted Flood Watches for interior counties in anticipation of the heavy rains, and Coastal Flood Advisories for the Western Shore of the Chesapeake.
"The heaviest rain is going to occur toward the afternoon and into the evening," said Steve Zubrick, science and operations officer at the National Weather Service's regional forecast office in Sterling, Va.
"That's going to fall on ground already saturated from last weekend's rainstorm. Streams and creeks are going to rise pretty rapidly. Hopefully people will heed their senses, and heed any signs put out by local authorities, and not drive around any barricades," he said. "I think [Thursday] afternoon will be quite a challenge for commuters, in places."
Flood Warnings were already posted for the Monocacy River near Frederick, on Thursday. The river was forecast to rise to 19.8 feet by mid-afternoon. That's almost 5 feet above flood stage, and further rises are possible, forecasters said. Flood Warnings were also posted for the Potomac River at Point of Rocks and Harper's Ferry, and Conococheague Creek at Fairview in Washington County..
In Baltimore, public works officials appealed to residents to clear trash from storm drains before the heavy rains start, and to report those they can't clear to the city's 311 service line. "Keeping them clear of trash and debris is crucial in preventing localized flooding," officials said in a statement.
The new rain could amount to nearly a month's worth in just 30 hours. It comes on the heels of 1 to 2 inches of rain on Sunday. That rain soaked the ground and filled streams, and forecasters said that increases the risk of flash flooding Thursday and Friday as the new precipitation begins to run off.
With this storm, Zubrick said, "we have a connection to the Gulf of Mexico, so that moisture is being pulled up into our area, and focused in our area, especially in the afternoon and evening. … And with the low-pressure system expected to go west of the Baltimore area, a prolonged period of east and southeast winds are going to pile up water in the bay … so we're looking at coastal flood issues."
"Talk about a change of plans in a short period of time," exclaimed another forecaster in Wednesday's online discussion from Sterling. "Last week I was worried about the possibility of a very bad wildfire season this spring. But that worry has rapidly turned into concerns over flooding."
The rain caps a long period of relatively dry weather for Central Maryland. Baltimore has seen below-average precipitation every month since October. The winter has also produce only 14 inches of snow at BWI-Marshall Airport. That's four inches below the long-term average there, and more than five feet less than last year.
The new storm was deepening Wednesday over the Gulf Coast states, and the counter-clockwise spin around the central low was driving very moist air from the Gulf and the Atlantic into the eastern states. There were flood watches, warnings and advisories in place from Louisiana to upstate New York in anticipation of the storm's passage.
A mixture of light rain, sleet and snow was already falling Wednesday afternoon in the higher elevations of Maryland's western counties. Rain was expected to start falling east of the mountains late in the day, becoming heavier overnight ahead of a cold front trailing the low.
One to two inches of rain was expected at BWI during the day Thursday, possibly accompanied by thunderstorms. A half- to three-quarters of an inch more was expected Thursday night, ending early Friday.
"By the time the front clears the area Thursday night, up to 3 inches of rain will be possible," the weather service said. "You should monitor later forecasts and be alert for possible Flood Warnings. Those living in areas prone to flooding should be prepared to take action should flooding occur."
The forecasts look great for Friday and through the weekend, with sunshine and highs in the 50s to near 60 degrees on Saturday.
(SUN PHOTO: Andre Chung, 2006)