People in parts of Colorado and Wyoming pulled puffy jackets, hats and umbrellas out of the closet again Wednesday for another round of wet spring snow.

The May Day snow storm was making travel difficult on some Colorado highways, where several crashes were reported late Wednesday, and along Interstate 80 in southeastern Wyoming. Denver's airport reported about 50 flight cancellations, and other flights were delayed for de-icing.

By midday, more than a foot of snow had fallen at Rocky Mountain National Park. The heavy snow caused power and heat outages there and in Cheyenne, which received 15 inches of snow by noon Wednesday. West of Cheyenne, 20 inches fell near Buford, while Casper saw 4 inches of snow.

Parts of the Midwest were also getting rare May snow.

South Dakota's largest city, Sioux Falls, got its first May snowfall in 37 years. The city received 1.5 inches of snow by late morning.

A winter storm warning was also in effect for parts of Minnesota and Wisconsin. Snow fell in parts of Nebraska, and western Iowa was expecting snow between Wednesday night and Thursday morning.

The storm is welcome in Colorado and Wyoming because it boosts the snowpack that provides the region's water supply. Both states are in a drought but have benefited from several rounds of spring snow. However, the recent storms have largely missed southwestern Colorado, which remains dry and at risk for wildfires.

About 5 inches were forecast for Denver, where the snow was making the roads a sloppy mess. The snow wasn't sticking much to the pavement, still warm after recent temperatures in the 70s, but it clung to grassy areas and flowers.

Denver native Chris Lujan said he's never worn a top coat, scarf and hat on May 1 before.

Greg Notz just put his hood up and wasn't fazed.

"I expect this. Yup. It's better than living where it's warm and dry and nice all the time. At least we get a variety," he said.

Snow hits Denver in May roughly once every three years. July and August are the only months that snow hasn't been recorded there, National Weather Service forecaster David Barjenbruch said.

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Associated Press writer P. Solomon Banda contributed to this report.