A storm parked over a huge swath of the Plains could produce days of flooding and violent thunderstorms from Nebraska to Texas, according to The Weather Channel.
Total rainfall over four-to-five days from Friday could approach all-time monthly records for the month of April in some parts of the High Plains, it added.
Meanwhile, nearly 700 flights were canceled coming into or out of Denver International Airport on Friday night as the city as the city braced for a storm that could dump more than a foot of snow in the region.
Up to 14 inches of snow could fall on Denver through Sunday morning, the National Weather Service said, and between 2-4 feet could fall in the mountains.
At least two tornadoes were reported in the eastern part of Colorado, one of which was accompanies by hail ranging up to 1.5 inches in diameter, the NWS said. No damage or injuries in the tornadoes were reported.
As of 7 p.m. local time (9 p.m. ET), there were 678 flights canceled for Saturday either coming into or out of Denver International Airport — or around 57 percent of its normal flight schedule, an airport representative said.
United Airline canceled all flights into or out of Denver altogether, the airport said.
The city and surrounding areas were under a winter storm warning Friday night. The storm is expected to change from rain to snow overnight and should wind down by Saturday night, the NWS said.
A tornado was also spotted touching down in Texas County, Oklahoma, on Friday, the National Weather Service said. It wasn't immediately clear if there was any damage.