The coldest air so far this season is spreading across the U.S.   

SIGNIFICANT COLD FRONT BRINGING COLD AIR, FREEZE ADVISORIES TO THESE PARTS OF THE US

Frost and freeze alerts

Frost and freeze alerts (Credit: Fox News)

Morning low temperatures will dip into the teens and 20s from the Northern Rockies to the Great Lakes.  

Below-average temperatures are expected for much of the country this week.

Forecast lows

Forecast lows (Credit: Fox News)

With cold air blowing over the Great Lakes, some lake-effect snow will accumulate.

Forecast snow

Forecast snow (Credit: Fox News)

The West will remain active with rain and mountain snow this week, and rain and storms will pop up along a stationary front draped across the southern Plains.  

Western storms

Western storms (Credit: Fox News)

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Flash flooding could be a problem for southeast Texas on Wednesday.