Rain or snow could fall across a big swath of the nation's midsection as holiday travel gets underway.

National Weather Service meteorologist Amy Seeley says parts of Illinois area could see rain switching over to snow on Christmas Eve, but it's impossible to predict yet where or how much will fall.

She says various computer models are showing differing forecasts and "aren't in agreement yet."

The National Weather Service says on its website that showers and thunderstorms across the Mississippi Valley are expected to strengthen Tuesday into Wednesday and move to the southeast, Mid-Atlantic and Southern New England.

Meanwhile, travelers from the Rockies to the Upper Great Lakes could see snow.