Widespread storms are expected to bring periods of intense rainfall to parts of the northern Mid-Atlantic and the Northeast on Thursday, and forecasters said that up to eight inches of rain could fall in some areas and raise the risk of a “potentially significant flash flooding event.”
Here are the key things to know:
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Washington and Baltimore could see some of the most intense rain. New York City issued a travel advisory.
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A severe thunderstorm watch, which means conditions are favorable for the type of storms that can deliver strong winds and hail, was issued early Thursday afternoon until 8 p.m. for an area that includes Washington, Baltimore, Philadelphia and New York City.
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Some areas in southeastern Pennsylvania and Northern New Jersey were already under flash flood warnings, which means flash flooding is imminent or already occurring.
The weather conditions leading to the bouts of heavy rain involve a cold front moving across the region. Richard Bann, a meteorologist at the Weather Prediction Center, an arm of the National Weather Service, said that the front was interacting with air that was unusually warm, humid and unstable this time of year.
“That’s going to allow the storms to become stronger,” he said. “With some very intense rainfall rates, upward of two inches per hour.”
By early afternoon, flight disruptions were rising at airports around the New York metropolitan area and along the East Coast, with hundreds of weather-related delays and cancellations stacking up.
Departures to Washington Dulles International Airport, Baltimore-Washington International Airport, Ronald Reagan Washington National Airport, La Guardia International Airport, Newark Liberty International Airport, Teterboro Airport and Philadelphia International Airport were grounded. This has resulted in flight delays two hours long and counting at some airports.
The Weather Prediction Center issued a Level 3 out of 4 risk for excessive rainfall for an area that includes Washington, Baltimore, Philadelphia and New York City through Friday. A wider area, from central Virginia to southern Massachusetts, including Richmond and Long Island, was under slightly lower risk. Flood watches were also issued across much of the region.
“Thursday’s storm system is expected to bring periods of heavy rain and potentially dangerous conditions to our city,” said Mayor Eric Adams of New York, where just two weeks ago heavy rains inundated the subways and led to flash flooding.
Forecasters highlighted two main areas of concern when storms begin to develop in the region on Thursday afternoon.
From northeast Pennsylvania through southern New England, rainfall of up to 1.5 inches per hour was expected. Forecasters said locally significant flash flooding was likely, particularly for areas close to the Poconos and the higher elevations of southern New England.
Farther south, the storms were forecast to be more intense. From northern New Jersey to Northern Virginia, up to three inches of rain per hour was expected, especially in the Washington D.C., and Baltimore areas, extending into southern New Jersey. The center said that some places were expected to get over five inches of rain.
Because the affected area includes major urban centers, including the I-95 corridor, Mr. Bann said that flash flooding could lead to serious disruptions, especially since repeated storms over the same locations were expected.
“It’s also been very wet in some of these places, like Washington D.C.,” he said. “The ground already has water in it, so any additional water on top of it is going to be more likely to run off as well.”
Once the front passes through, the outlook is looking drier and cooler from Friday.
“There might be some lingering rain along the coast,” Mr. Bann said. “But the heavier activity will have gone.”
Christine Chung contributed reporting.
Nazaneen Ghaffar is a Times reporter on the Weather team.
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