Blizzards dumped up to 3 feet of snow in parts of the Midwest (Representational image)
Extreme weather hit the US on Monday, putting over half the population of more than 200 million people under threat.
Severe storms across the East led to about 4,000 flight cancellations and early school closures, causing major disruptions in New York, Chicago, and Atlanta.
Blizzards dumped up to 3 feet of snow in parts of the Midwest, while Hawaii faced flooding and landslides after heavy rain.
Meanwhile, a heat wave pushed temperatures near 100°F in the Southwest, far above normal for March.
Federal offices in Washington shut early as a precaution, though the worst storms did not fully develop.
Forecasters warned of strong winds and possible tornadoes from Maryland to South Carolina, followed by a sharp drop in temperatures across the East Coast.