Snow, sleet and hail have snarled transportation across swathes of the US during one of the busiest travel weeks, and dozens have died in storms over the Christmas holiday period.
More than 40 people were killed by tornadoes and floods in the US during the holiday season, where rare winter tornado warnings were issued in Alabama on Monday.
Alabama, Mississippi and the Florida panhandle were expected to bear the brunt of the day's strongest storms, AccuWeather senior meteorologist Michael Leseney said.
More than 2900 flights had been cancelled at US airports by 7pm eastern standard time on Monday (1100 AEDT on Tuesday), according to FlightAware.com, while another 4000 delays were reported.
Chicago-area airports were worst hit with hundreds of flights cancelled as the city was swept by sleet and hail.
More than 30cm of snow was forecast for southwestern Wisconsin and southeastern Minnesota, and snow was also falling in Iowa, Nebraska and Missouri.
A flash flood warning was in effect in eastern Missouri and Southern Illinois, the National Weather Service said. Thirteen people died in flash floods in those two states during the weekend.
The bad weather caused two candidates for the Republican presidential nomination, New Jersey Governor Chris Christie and US Senator Marco Rubio, to cancel campaign events in Iowa.
In Arkansas, a 31-year-old man drowned in a flood-swollen creek northwest of Little Rock, authorities said on Monday. Six tornadoes were reported on Sunday - three in Arkansas, one in Texas, and two in Mississippi.
US President Barack Obama, on vacation in Hawaii, called Texas Governor Gregg Abbott on Monday to receive an update and to offer his administration's continued support after weekend tornadoes that killed at least 11 people in the Dallas area and damaged about 1600 structures and homes.
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One twister in the city of Garland, Texas, had winds of up to 322km/h and killed eight people.
"We are very blessed that we didn't have more injuries and more fatalities," Garland's Mayor Douglas Athas told CNN.
In the Dallas suburbs of Garland and Rowlett, which were devastated by tornadoes on Saturday, many residents turned to social media to tell stories of survival.
Briana Landrum posted a photo of her living room couch surrounded by wreckage where her house once stood in Rowlett.
"The roof fell on us one second and the next, it was gone," she wrote. "The tornado ripped our world apart."
Ten deaths and 58 injuries were reported in Mississippi, and hundreds of homes were damaged, authorities said.
In flooded southern Missouri, dozens of adults and children forced from their homes took refuge at Red Cross shelters.
In Oklahoma, Governor Mary Fallin extended a state of emergency for all 77 counties on Monday after freezing rain, ice and sleet left nearly 200,000 homes without power.
