Story highlights Weather events have caused four deaths across hardest hit states

Hardest hit states are Oklahoma, Kansas and Missouri

(CNN) It's a dangerous setup that the Central Plains of the US knows all too well, as residents find themselves in the middle of cold, Arctic air blowing down from Canada and much warmer, humid air streaming in from the Gulf of Mexico.

During the spring and fall, this clash of air masses often spawns severe storms and tornadoes -- but during the winter, the result can be an equally devastating, and much more widespread ice storm.

Cold Arctic air meets warm air from the Gulf of Mexico, setting the stage for an ice storm.

Beginning on Friday and lasting through the weekend, a slow-moving storm has been developing over the Southwestern US and is expected to bring a stretch of precipitation across the midsection of the country. With cold air at the surface and warmer air from the south moving on top of the cold, this precipitation will fall as freezing rain or sleet for long periods of the weekend for over a dozen states, from Texas all the way to Maryland.

More than 30 million Americans are under some type of wintry watch, warning or advisory from this storm, and 10 million of those fall under an ice storm warning, which is where most of the significant impacts from the storm will occur.

The hardest hit states of Oklahoma, Kansas and Missouri will see up to one inch of ice coating trees and roads -- making travel impossible and potentially bringing power outages to millions of residents this weekend.

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