McLEAN, Va. – A couple degrees will make a huge difference in the lives of commuters from Missouri to the East Coast over the next two days as a pair of winter storms prompted weather advisories and warnings for 25 million Americans.

Some areas could see a foot of snow, others could just see ice, snow or rain – or a “mixed bag of glop,” forecasters said. The exact line of demarcation is impossible to forecast, AccuWeather senior meteorologist John Gresiak told USA TODAY.

“Monday morning will see a band of snow from Indiana eastward all the way to New Jersey,” Gresiak said. “South of that will be a mixed bag of glop – sleet and freezing rain – and below that, just rain.”

The snow started Sunday morning in St. Louis, where the first storm was forecast to drop up to five inches before giving way to freezing rain and drizzle Sunday night. A second hit Monday will bring a mix of rain, snow and sleet before a bit more snow falls in the afternoon, forecasters said.

Some areas in northern and central Missouri into Illinois could see a foot of snow before the system moves out late Monday, Gresiak warned. A few dozen flights were delayed or canceled Sunday at St. Louis Lambert International Airport.

“Conditions are deteriorating and crashes are occurring” on many roads, the state Public Safety Department tweeted Sunday. “Remember, you might be an excellent driver in the snow. That doesn’t help if the motorist who hits you isn’t.”

Ohio was a precipitation melting pot. All 52 counties could experience the four precipitation types – rain, snow, sleet and freezing rain – from Sunday night into Monday night, the National Weather Service forecast. Commuters across the state could see slick spots Monday morning, the service warned.

“The main weather concern will be the changeover to snow and accumulations overnight into early Tuesday before the precipitation ends,” the weather service said.

The Monday morning commutes in Indianapolis, Pittsburgh, Baltimore and Philadelphia will feature some slick spots and commuters may have to allow for some extra time.

Jason Puma, a meteorologist with the National Weather Service in Indianapolis, said the second phase of snow will come by late afternoon or early evening Monday into Tuesday. Forecasts could change, he stressed.

 “Be prepared for changes, and be prepared if they plan on driving to allow extra time,” Puma said.

Residents in and around Washington, D.C., were bracing for a wintry mix forecast to sweep across the region Monday morning. Rain and snow were forecast Sunday night into Monday, with rain taking over from there as higher temperatures greet the second storm.

New York state and New England might not be so lucky, AccuWeather said.

“There is likely to be a narrow swath of 6- to 12-inch snowfall totals in the Northeast, but confidence remains low on exactly where that stripe will occur,” said AccuWeather Senior Meteorologist Rob Miller. But between the snow and rain will be a “corridor of potentially significant icing,” Miller said.

Portions of central and eastern Pennsylvania into southern New England can have up to a quarter of an inch of icy glaze on elevated surfaces like hand railings, trees, and power lines. Any untreated surfaces would also become very slippery.

“Around a quarter of an inch of ice on trees and power lines is enough to begin causing some damage and can lead to some localized power outages,” Miller said.

Contributing: Segann March, Cincinnati Enquirer; Domenica Bongiovanni and Crystal Hill, Indianapolis Star

USA Today