At least two people were killed, hundreds of thousands of premises were left without power and thousands of flights were cancelled or delayed after intense storms lashed much of the eastern United States.
Millions of people on Monday were under severe weather alerts, including tornado watches, as rain, strong winds and hail swept east along nearly the entire eastern seaboard, from Alabama to New York.
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The National Weather Service (NWS) had predicted a “moderate risk” of hazardous storms, with gusts up to 80 miles per hour (130kmph).
“Stay weather aware and make sure you have multiple ways to receive warnings,” the NWS in Baltimore and Washington, DC said on social media earlier in the day.
The storms’ spread was massive, with tornado watches and warnings posted across 10 states from Tennessee to New York. The NWS said the area of greatest concern centred in the Washington-Baltimore region.
As much of the severe weather danger subsided into the late evening, some areas faced flood threats as it continued to rain.
Hail as large as 4.5 inches (11.5cm) in diameter was recorded in Virginia, the NWS said.
In Alabama, a 28-year-old man died after being struck by lightning in an industrial park, a local ABC station reported. And in South Carolina, a 15-year-old was killed when he was hit by a falling tree outside his grandparents’ house, according to a local CBS station.
By late Monday, more than 700,000 premises had lost power along the East Coast, according to tracking website Poweroutage.us.
More than 1,700 US flights were cancelled on Monday and some 8,000 delayed as the severe weather loomed, the FlightAware website said.
More than a quarter of the cancellations were at Hartsfield-Jackson Atlanta International Airport, which was digging out from disruptions caused by Sunday storms.
The Federal Aviation Administration said it was rerouting planes around storms heading to the East Coast and warned it would likely start pausing flights in and out of the New York City area, Philadelphia, Washington, DC, Charlotte and Atlanta.
In Washington, DC, federal agencies sent employees home early, at 3pm (19:00 GMT), in anticipation of the weather.
The storms came as large parts of the southern United States, including Texas, Louisiana and Florida boiled under excessive heat warnings, with temperatures up to 108 degrees Fahrenheit (42C) predicted through Tuesday.
Scientists say climate change has amplified the intensity and frequency of extreme weather events around the world.