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Maryland Weather Meteorology, astronomy and climate conditions in the Baltimore region

Maryland weather: Flood warnings extended to Thursday afternoon as streams, rivers remain high

Relief from one of the Baltimore region’s wettest stretches on record arrived Thursday, but flood warnings nonetheless remained in effect through the afternoon and evening after another round of soaking rain fell Wednesday night.

Sunshine and highs in the upper 80s are forecast Thursday and for the next several days, though there are chances for storms Friday and again Sunday. Wet weather is likely to resume next week.

Still, after another bout of heavy rain Wednesday, flooding was occurring along the Patapsco River near Catonsville, the Gunpowder Falls in northern Baltimore County, the Monocacy River in Carroll and Frederick counties and the Susquehanna River. The National Weather Service warned that other streams in the area may be experiencing flooding.

There were brief fears that historic Ellicott City was teetering on the brink of another devastating flood — with police shouting through bullhorns to advise anyone on Main Street to seek higher ground Wednesday night. Howard County officials later said the rain was not heavy enough to overwhelm the channels that carry streams through the old mill town to the Patapsco River.

Many roadways remained impassable because of flooding Thursday, including Defense Highway near Rutland Road and Dorsey Road at Central Avenue in Anne Arundel County, and two southbound lanes of Belair Road near Honeygo Boulevard in White Marsh. The closures were among nearly 200 forced by flooding and debris since Saturday afternoon, according to the State Highway Administration.

Road closures were numerous in Baltimore County and Carroll County. Baltimore County officials reported a dozen flooded roads Thursday morning, from Catonsville to Monkton. In Carroll, state highway officials reported closures on Old Manchester Road, Green Valley Road and Old Washington Road.

Authorities reported making multiple water rescues Wednesday night in Carroll County, though no injuries were reported. Baltimore County emergency officials said crews have responded to 32 water-related incidents since heavy rains began Saturday.

In Harford and Cecil counties, officials were closely watching conditions at the Conowingo Dam, fearing flooding for communities downstream on the Susquehanna River. By Thursday morning, operators opened 17 of the dam’s 50 spill gates to prevent rising waters from causing flooding above the dam. That was raising concerns of flood risks in Port Deposit and Havre de Grace.

The river is expected to continue rising until Friday morning, and Port Deposit Mayor Wayne Tome Sr. said officials believe that as many as 22 to 27 gates will need to be opened by midnight Friday. That could require electricity to be shut off in the Cecil County town “at some point,” said Tome, who is also EMS chief for the Water Witch Fire Company.

Meteorologists warned motorists that although the rain has stopped, the soaked ground could allow trees to fall with little or no wind. A downed tree on southbound Interstate 83 caused severe traffic backups Wednesday morning; the tree has since been removed.

In Baltimore City, volunteers with the American Red Cross reported several cases of flooded basements and ruined water heaters after canvassing flood-prone neighborhoods along the Frederick Avenue corridor.

A spokesman said the Red Cross is keeping open the doors of its emergency shelter in the northwest part of the city for anyone displaced by flooding. “This is a just-in-case scenario,” spokesman Richard McIntire said. The facility can hold around 100 people, he said

As of Thursday morning, 15.43 inches of rain had fallen in July at Baltimore/Washington International Thurgood Marshall Airport, a record-breaking total. The previous July record, set in 1889, was 11.03 inches for the month. This month’s precipitation is about 12.17 inches above normal rainfall levels for July.

“We could still go well above the record if the pattern continues like this,” said Isha Renta, a National Weather Service meteorologist.

Tuesday also set a daily rainfall record for July 24. At BWI, 4.07 inches of rain fell Tuesday, more than doubling the previous daily rainfall record for that date, 1.73 inches, set in 1961.

This July is already Baltimore’s second-wettest month on record, surpassing August 1933 and behind only August 1955, both of which were associated with historic tropical cyclones.

It has also been Baltimore’s wettest summer on record so far. The area has seen more than 20 inches of rain in June and July, about 3½ inches more than the second-wettest June-July period on record in 2015. Since May 1, more than 28 inches of rain — about two-thirds of Baltimore’s typical annual rainfall — has fallen, 6 inches more than the previous record for that period, from 1989.

And most of the precipitation has come in just the past ten days. Just a few hundredths of an inch of rain fell during the first half of July, the second-driest for that period on record in Baltimore, according to the weather service.

The amount of moisture in the atmosphere is akin to a tropical storm, only instead of passing in a day or two, it’s coming in a persistent, robust stream straight from the Bahamas, meteorologists said. A low-pressure system over the Southeast and an area of strong high pressure off the coast are acting like gears in a conveyor belt, spinning tropical air northwestward — directly into Maryland, Virginia and North Carolina.

“We’ve got a direct conduit to the tropics, and it’s pretty unusual,” said Eric Luebehusen, a meteorologist with the U.S. Drought Monitor who runs an email listserv focused on Baltimore-area weather. “You basically have tropical moisture converging on the mid-Atlantic. That’s an ugly setup.”

The levels of atmospheric moisture are at a record high for July, he said.

That pattern was disrupted for the first time in days Thursday, when high pressure moved over the region, giving it a break from the onslaught of moisture. Though humidity remains relatively high, precipitation is not in the forecast for at least a day.

But rain clouds could return late Friday as temperatures approach 90 degrees, stirred ahead of an advancing cold front. Rain showers are also possible along another front passing through Sunday.

Then, meteorologists say, the tropical conveyor belt could reappear by early next week, bringing another stretch of heavy rain.

Baltimore Sun Media Group reporters Christina Tkacik, Sarah Meehan and David Anderson contributed to this article.

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