A blast of cold air being dragged southward by a dip in the jet stream dumped snow in the Rockies, Plains and parts of the Midwest on Wednesday in a snowfall that meteorologists said could be “historic” for this time of year.

Up to 18 inches of snow is forecast for the mountains of Colorado and Wyoming, where heavy snow started falling Tuesday. Several inches could also fall by the end of the week in a band from Texas to Wisconsin, according to the National Weather Service.

Some portions of the Plains and upper Midwest regions, including Wisconsin and sections of Minnesota, could see a flurry of wet snow on Wednesday night into Thursday, Weather.com reported. A light early May dusting may even be seen as far south as the Texas Panhandle and western Oklahoma.

Cheyenne, Wyo., had already received more than 6 inches of snow early Wednesday morning, Weather.com reported.

The National Weather Service reported winter storm warnings were in effect for portions of north-central Colorado, southern Wyoming and southern Minnesota.

AP

Snow clings to flowers in Denver on Wednesday. As much as a foot of snow is forecast for some areas of Colorado.

With the jet stream bowing to the south, cold air is being sucked deep into the country, bringing temperature changes that may seem downright cruel to many, according to meteorologists at Weather.com.

Amarillo, Texas, is the perfect example. On Tuesday it hit a high of 97 degrees.

“By tomorrow morning we have … Amarillo at 30 and probably snowing,” Weather Channel meteorologist Kevin Roth said. “So in Amarillo we’re projecting a 67-degree drop from Tuesday afternoon to Thursday morning – so summer to winter.”

Minneapolis, Kansas City and Des Moines, Iowa, have been basking in the 70s and 80s. They’ll be lucky to see 40 through the end of the week, weather.com said. And Chicago just had its first 80-degree day of the season. It should have another on Wednesday before highs drop to the 50s and low 60s through the weekend.

The heaviest snowfall will be along the Front Range of the Rockies, with an area from central Colorado to southeastern Wyoming under winter storm warnings that call for up to 20 inches of fresh snow through Wednesday night. Just to the east, cities in the foothills, including Denver, could see five to eight inches of accumulation during the period, and roads could become icy and snow-packed, the weather service said.

Further east, where the cold air meets the warm, severe thunderstorms are likely Wednesday in parts of Kansas, Oklahoma and Texas, according to weather.com, which adds that the threat diminishes Thursday, with “marginally severe” storms possible in parts of Texas and southern Louisiana.

Travel disruptions could come with the worst parts of the storm, with Interstates 25 and 80 between Wyoming and Colorado in line for possible snow and ice, Roth said. But as of Wednesday morning, FlightAware.com listed only 16 canceled flights in the region, all at Denver International Airport.

“That will probably go up during the day,” Roth said.

While the storm may set some snow records, May is often a fickle month. Heavy snow is fairly rare, but temperatures in different parts of North America can range radically, Roth said.

Montreal, Quebec, and Ottawa, Ontario, for example, will be 30 to 40 degrees warmer on Thursday than normally toasty Oklahoma City, he said.

Cheyenne, Wyo., which hit 70 degrees Tuesday afternoon, was on the verge Wednesday of breaking its May snowfall record of 14 inches, Roth said.

“Cheyenne had eight inches as of midnight their time, and it’s been snowing steadily since that,” he said. “We think they’re going to end up with a good 12 to 18. … Welcome to May, right?”

NBC News’ Matthew DeLuca contributed to this report.

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This story was originally published on Wed May 1, 2013 6:00 AM EDT