This month is ending as Baltimore’s wettest July in history, by far, but that’s only the beginning of the rainfall records set recently.
Through Monday, there was 16.67 inches of rain this month at Baltimore-Washington International Thurgood Marshall Airport. Normal July rainfall is about 4 inches .
The total is less than 2 inches from a record for Baltimore’s single wettest month, set in August 1955, when back-to-back tropical cyclones hit the region. Though showers are possible around the region Tuesday afternoon and evening, it’s unlikely enough rain will fall to match or break the 18.35-inch record.
Here are some of the marks that have been added to Baltimore’s record books, according to the National Weather Service:
» Three daily rainfall records: 3.35 inches July 17, 4.79 inches July 21 and 4.07 inches July 24.
» The wettest two-week period on record: 16.37 inches during a stretch ending July 28. The old record was 15.93 inches during August 1955.
» The wettest July on record. The old record was 11.03 inches in 1889.
» The wettest 90-day period on record, with 29.61 inches from May 2 through July 30. The old mark was 27.01 inches for the 90 days ending Oct. 31, 2011, a period that included Hurricane Irene and Tropical Storm Lee.
» The wettest March-through-July period on record, also 29.61 inches. The old record dated to 1889, with 24.02 inches of rain.
The heavy rains over the past week and a half have washed millions of gallons of sewage into Chesapeake Bay waterways, including Baltimore's Inner Harbor, along with unknown amounts of nitrogen and sediment pollution.
Jason Elliott, hydrologist with the weather service’s Baltimore/Washington forecast office, noted that the year-to-date rainfall at BWI, 41.36 inches, is already higher than the annual totals for 67 separate years in Baltimore.
“We’re literally half an inch away from the normal annual rainfall, and it’s not even August yet,” he said.
It’s also remarkable given that this month’s rain tied to tropical storm activity — as is typically the case with rainfall records, Elliott said. This July’s rain came largely from a normal but unusually strong and persistent weather pattern that sent tropical moisture flowing directly into the mid-Atlantic.
The deluge was widespread, but most heavily concentrated across a slice of the middle of the state.
During a 10-day period, when the heaviest and most persistent rain fell, National Weather Service radar estimates show accumulations between 10 inches and 15 inches likely fell across a sliver of the state from Calvert County to Baltimore and Carroll counties.
That includes much of Anne Arundel County, and isolated portions of Montgomery and Harford counties.
The heaviest spot of all might have been near the Brooklandville area, a rural section of Baltimore County between Cockeysville and Owings Mills, where meteorologists estimate between 15 and 20 inches of rain fell during a single week.
Radar estimates for the full month show similar concentrations, with 15-20 inches from Glen Burnie to Manchester, including the western half of Baltimore and the Owings Mills, Reisterstown and Hampstead areas.