A major winter storm that broke snowfall records in the Midwest is now slamming the mid-Atlantic and causing the cancellation of more than 2,000 flights across the U.S.
Ronald Reagan Washington National Airport is the hardest-hit airport.
More than 50 million Americans from Kentucky to Washington, D.C., remain under winter alerts as the last of the storm pushes through Monday afternoon.
Heavy sleet and freezing rain struck Illinois, Indiana and Kentucky, causing power outages, while snow is targeting the Washington, D.C., area.
Schools are closed in Philadelphia, Baltimore and D.C. and states of emergency are in effect in West Virginia, Virginia and Maryland.
Five to 6 inches of snow has been reported around the D.C. area.
Hundreds of D.C. residents of all ages descended on Meridian Hill Park for a massive snowball fight, including ABC News chief meteorologist and chief climate correspondent Ginger Zee.
"When do adults get to have this kind of fun?" D.C. public school teacher Tiik Pollet told ABC News. "You get to just chill -- literally -- and be kids again."
"You know how rare it is to get decent snowfall in D.C.? So, we want to have some fun with it," said one of the event organizers, Michael Lippin.
Federal offices are closed in D.C., where a snow emergency is in effect until at least the end of Tuesday, officials said.
D.C. Transportation Department Director Sharon Kershbaum told ABC News Live that the city has been preparing for weeks and has geared up nearly 250 snowplows.
"if you don't need to travel, please don't," she said, adding, "Our priority is to make sure that Congress can get where they need to."
Although federal offices are closed, Congress gathered on Monday for a joint session to certify the results of the 2024 election, the final step before President-elect Donald Trump's inauguration on Jan. 20.
Another batch of snow could move through D.C. on Monday evening.
Before reaching the East Coast, this storm hit the Midwest on Sunday.
MORE: 1 dead, 1 injured after ski group triggers avalanche in WyomingSnowfall totals topped 1 foot in Kansas and Missouri, while over 10 inches of snow has been recorded at Cincinnati/Northern Kentucky International Airport.
Nine fatalities have been attributed to the storm: two in Missouri, two in Kansas, three in Virginia, one in North Carolina and one in West Virginia, officials said. All were related to car crashes or drivers otherwise losing control of their vehicles on slick roads.
President Joe Biden and his team are closely monitoring the storm, a White House spokesperson said.
ABC News' Alex Faul and Emily Chang contributed to this report.