(CNN) — Bundle up; it's about to get chilly.
We're not talking about a nip in the air, either. By midweek, locales throughout the United States will have seen high temperatures up to 20 degrees below average, according to CNN and National Weather Service forecasters.
As a cold front moves through the Plains and Great Lakes toward the Eastern United States -- bringing some light snow, especially in the higher elevations of the Appalachian Mountains and in areas impacted by lake effect -- temperatures are expected to drop significantly beginning Monday.
The Plains could see high temperatures 15 to 20 degrees below average Monday and Tuesday. By Wednesday, the chill will grip the Northeast and Southeast, pushing the mercury about 20 degrees below average.
"A strong front extending from the Great Lakes to the Central Plains will move eastward off the East Coast and southward to the Gulf of Mexico by Tuesday evening. Cold high pressure over South-Central Canada will sink southward to the Middle Mississippi Valley/Central Plains also by Tuesday evening," according to the National Weather Service.
Residents from the Missouri Valley to the northern Rocky Mountains can expect snow Monday, the weather service said.
Rain or snow can be expected Tuesday through much of the Great Lakes area, down to Tennessee and eastward toward the Carolinas and southern New England.
"Meanwhile, a front over the Eastern Pacific will move to the West Coast and dissipate on Tuesday morning. The system will produce light to moderate rain along the West Coast from the Pacific Northwest to Northern California late Monday night to Tuesday morning," the weather service said.
The Centers for Disease Control and Prevention has tips for how to stay warm and what to do in the event of cold-related illnesses.