The leading edge of the Arctic air filtering into the U.S. is abrupt and ruthless—temperatures in Iowa at 4:00 PM ranged from 72°F in the southeastern corner of the state and 27°F with a wind chill of 11°F in the northwestern corner of the state. Ahh. Or brrr, depending.

A dangerous multi-day severe weather outbreak is ramping up across the southern United States at this hour, with a powerful squall line stretching from St. Louis to the Gulf of Mexico. Millions of people are at risk for widespread wind damage, large hail, and even tornadoes.

An incredibly long and impressive line of thunderstorms swept through the central United States on Thursday night, stretching more than 1,200 miles long at its largest extent. The storms left more than 300 of reports of damaging winds and large hail in its wake.

This afternoon's satellite imagery shows an incredible slug of dry air moving across the south and east behind a cold front, bringing beautiful weather to millions of people. In fact, the air is so dry at 10,000 feet above sea level that its humidity is near zero percent in some spots.

One of the cooler results of the NotReallyAPolarVortex sweeping across much of the United States is that it allows us to see just how much of an effect the sun and water have on our weather.