NORMAN, Okla. (AP) – The weather outside will be frightful for some holiday travelers this weekend, with snow stretching from the Rocky Mountains to the upper Midwest on Christmas Eve and possible severe weather in the middle of the U.S. on Christmas Day. Forecasters cautioned travelers to keep alternate routes in mind and prepare for possible delays.

There is a blizzard watch posted for much of the Dakotas and a winter storm watch in effect from Montana to Lake Superior. The Storm Prediction Center cautioned that warm, humid air would bring possible severe weather to the Plains states on Sunday – reaching as far north as Omaha, Nebraska.

A lesser threat of severe weather extended southward into Arkansas and Oklahoma, where the atmosphere would be warm but more stable.