Torrential rain from a new storm out of the south lashed an already saturated Maryland overnight, as emergency officials braced for what could be a scene of widespread damage and disruption this morning.
Forecasters were warning of an additional 3 to 5 inches of rain last night and today - with downpours of up to 8 inches in especially unlucky locations.
"It's not good news," said Bob Oravec, lead forecaster at the National Hydrometeorological Prediction Center in Camp Springs. Streams already at flood stage "are not going to be helped by additional runoff," he said.
While there were no confirmed deaths yesterday from the rain and flooding, rescue workers were searching for two missing teenage boys after the father of one of them found a bicycle and clothing by a bridge at Little Pipe Creek near the border of Frederick and Carroll counties, state police said.
An apparent tornado touched down near Chaptico in St. Mary's County shortly after 6 p.m., destroying two barns and damaging several homes and an automotive repair shop, said Tim Cameron, the county's director of public safety. Another was sighted near Mechanicsville. No injuries were reported, he said.
Around the state, local officials were urging residents of low-lying areas to move to shelters. The Susquehanna River was expected to crest above major flood levels in Harrisburg, Pa., tomorrow - with potentially devastating consequences for Maryland towns downstream and the Chesapeake Bay.
Meanwhile, state officials said they would meet with the Federal Emergency Management Agency to begin tallying uninsured damage to determine whether Maryland qualifies for disaster assistance.
The latest culprit in a five-day meteorological mugging of the Mid-Atlantic region is a storm that made landfall yesterday afternoon in the Carolinas. Radar estimates indicated that the storm was dropping 3 to 5 inches of rain as it moved into eastern North Carolina. That intensity was expected to carry across Virginia and Maryland, Oravec said.
"It should be passing the Chesapeake Bay around midnight [last night], then up towards the New York City area by early [this] morning," Oravec said. "It's actually moving pretty quick."
The expected downpours could bring a return of flooding to many of the same places that were soaked by up to a foot of rain delivered by a low-pressure system that had camped over the region starting Friday. The National Weather Service released figures yesterday morning showing that Bel Air had received 12.29 inches of rain over a four-day period - while Columbia, Hyattsville and several locations in Montgomery County exceeded 10 inches.
The latest storm was expected to bring new troubles in the form of storm surges - particularly along the west side of the Chesapeake Bay.
That's due in part to persistent winds from the south and southeast that have been pushing water into the bay and holding it there. The low pressure and recent new moon might also contribute to the high water, Oravec said.
Storm surges during Tropical Storm Isabel in 2003 reached 8 to 10 feet and caused extensive damage to Fells Point, Annapolis, eastern Baltimore County and other areas. But officials weren't expecting anything so serious this morning.
Ed McDonough, a spokesman for the Maryland Emergency Management Agency, said yesterday that officials were expecting a storm surge of about 2 to 3 feet at high tide. Officials in Anne Arundel County issued a coastal flood watch.
The tropical system racing up the bay was also expected to bring stronger winds than the system that brought soaking rains to the region over the weekend. Oravec said the storm's sustained winds might reach 20 mph, with gusts to 40 or 50 mph in thunderstorms. That's not normally enough to topple trees, he said, "but with the amount of water in the soil, it won't take much."
"I would expect more trees down," said Dave Buck, a spokesman for the State Highway Administration.
As heavy rains continued to pound Western Maryland yesterday, forecasters were expecting flooding on the Potomac and Monocacy rivers by late tomorrow. McDonough said the state anticipates that the Potomac will crest about 2 to 3 feet above flood stage at Point of Rocks in Frederick County - a moderate deluge for a town familiar with 8- to 10-foot floods.
Meanwhile, the Susquehanna is expected to reach flood stage at Harrisburg by late today and rise to as much as 8 feet above flood stage there by tomorrow evening, Oravec said.
The National Weather Service was projecting that the river would reach 25.1 feet at Harrisburg - not even counting the effect of last night's rains. That would exceed the level reached in a January 1996 flood, which damaged the Cecil County town of Port Deposit.
Ben Armstrong, spokesman for Exelon Corp., which operates the Conowingo Dam, said that when 14 of its gates are open, water floods Route 222. The town of Port Deposit begins to flood when 22 gates are open. In the 1996 storm, 39 floodgates were opened.
Environmentalists are worried that runoff from the Susquehanna watershed, which supplies half the fresh water to the Chesapeake Bay, could create bigger "dead zones" in the bay this summer.
Twice in the past decade - after the 1996 storm and in September 2003 - floodwaters washed huge amounts of nutrients into the bay, triggering record levels of oxygen-robbing algae blooms and reports of areas unable to support aquatic life.
The damage was mitigated somewhat in those cases because the storms came outside the peak seasons for spawning animals and plant growth.
The region wasn't so lucky in the summer of 1972, when Tropical Storm Agnes destroyed oyster beds, dumped millions of tons of sediment in the bay and scoured away more than half of all bay grasses.
"Is it going to be like Agnes? I don't think so," said John Page Williams of the Chesapeake Bay Foundation. "Is it going to have an effect? Yes, it will."
Chuck Gates, a spokesman for the Maryland Department of the Environment, said that none of the dams on the Western Shore had problems as of yesterday, but that five, small "low-hazard" dams in Dorchester County had been breached as a result of heavy weekend rains.
Gates said the dam failures had caused no injuries or property damage but might have done environmental damage to river basins.
Central Maryland and the Eastern Shore received a brief respite yesterday before a new line of storms - part of the same low-pressure system that has been camped over the region since Friday - passed through the Baltimore area in the afternoon.
After a miserable Monday, local commuters got a bit of a break during yesterday's morning rush, Buck said. While some roads were closed - particularly along a stretch of Route 450 in Anne Arundel County that remained under water all day - there were far fewer problems than 24 hours earlier.
Buck wasn't particularly hopeful about today. He said an additional 3 to 5 inches could bring significant flooding and road closings.
Meanwhile, local officials were preparing for a wet and wild night.
In Baltimore, city transportation officials asked residents of low-lying areas such as Fells Point, Canton and Locust Point to look out for flooded streets and avoid parking close to the harbor.
Concerned about the potential for flooding in shoreline areas, Baltimore County officials designated Stemmers Run Middle School for use as a temporary shelter - and with water rising last night in the Turners Station community and on the roads on Millers Island in eastern Baltimore County, emergency planners suggested that residents consider evacuating.
At 8:45 p.m., two county buses were dispatched to travel the three main roads on Millers Island searching for residents seeking transportation to the middle school.
As streets flooded in the Sollers Point area, 35-year-old Sonia Johnson left her home and loaded her three children in a car to seek overnight shelter in the school. "My kids are scared," she said as she drove off about 11 p.m. - unable, she said, to find her mother and sister, who live nearby.
Officials said that the shelter would remain open as needed, and that people could bring their pets. Animal control officials would transport the pets to a facility where they would be housed until owners could retrieve them.
"One of our major concerns is flooding," said County Executive James T. Smith Jr. "The ground is so saturated that any heavy rainfall is virtually certain to cause flooding, especially in low-lying areas."
Anne Arundel officials were urging residents along Brockbridge Road in Maryland City to evacuate because of concerns about the Patuxent River after floodgates were opened on the T. Howard Duckett Dam at Rocky Gorge Reservoir.
In Harford County, an automated calling system operated by the sheriff's office was alerting residents in flood-prone areas to evacuate, said Rich Gardiner, a spokesman for the Bel Air Volunteer Fire Company. A shelter was set up at Harford Technical High School in Bel Air.
Along Little Pipe Creek, the missing teens - identified as Michael White, 14, and Tom Plunkard, 15, by the younger boy's sister - apparently had checked out flooding conditions late in the afternoon on the Frederick County side of the border. The search effort included police with dogs, a helicopter, firefighters, relatives and neighbors - all to no avail. The search was suspended at 11:15 p.m., and was to resume at daybreak.
"The current's a true hazard," State Police 1st Sgt. Chris Sasse said of the storm-swollen creek as the search was ending, adding that the water level appeared to have risen 5 feet since dinnertime.
Sun reporters Nick Shields, Candus Thomson, Justin Fenton, Daniel P. Clemens Jr., Anica E. Butler and Ellie Baublitz contributed to this article.