The National Weather Service on Thursday posted flash flood warnings along parts of the Northeast urban corridor stretching from the Washington-Baltimore region north through Philadelphia, Wilmington, Delaware, and into Newark, New Jersey, and the New York City metropolitan area.
Severe thunderstorm watches were also in effect across much of the Interstate-95 corridor, but forecasters said flash flood risks were starting to fade Thursday night.
Stormy weather during the day appeared to be a key factor disrupting commercial air travel across the Northeast.
The eight major airports serving the region - Washington Dulles, Baltimore-Washington, Ronald Reagan Washington National, Philadelphia, Newark Liberty, LaGuardia, John F. Kennedy International and Boston Logan - accounted for the cancellation of at least 1170 flights into, out of or within the US, according to online flight tracking service FlightAware. Hundreds more flights were delayed.
Passenger rail travel was also hampered, with Amtrak reporting service suspended between Philadelphia and Wilmington due to severe storms flooding the tracks. Service was restored about two hours later as water receded, but "residual delays" were expected, Amtrak said on X.
A daily rainfall outlook map issued by the Weather Prediction Center put the risk of "excessive" showers capable of triggering flash floods at 40 per cent or higher for a swath of the mid-Atlantic and Northeast that is home to 37 million people.
Up to 13cm of rain was forecast in the heaviest bands of showers across New York City, Long Island and the Hudson River Valley.
The Weather Service attributed the storm threat to a cold front that was bringing a combination of unstable air mass and exceptional amounts of atmospheric moisture to the region.
