SIOUX FALLS, South Dakota (AP) – The deep freeze expected to arrive tomorrow in parts of the United States will be one to remember, with potential record-low temperatures heightening fears of frostbite and hypothermia. It hasn’t been this cold for decades – 20 years in Washington, D.C., 18 years in Milwaukee, 15 in Missouri – even in the Midwest, where bundling up is second nature. Weather Bell meteorologist Ryan Maue said, “If you're under 40 (years old), you’ve not seen this stuff before.” Blame it on a “polar vortex”, as one meteorologist calls it, a counterclockwise-rotating pool of cold, dense air. “It’s just a large area of very cold air that comes down, forms over the North Pole or polar regions ... usually stays in Canada, but this time it’s going to come all the way into the eastern United States,” said National Weather Service meteorologist Phillip Schumacher in Sioux Falls, South Dakota. The frigid air – a perfect combination of the jet stream, cold surface temperatures and the polar vortex – will begin tomorrow and extend into early next week, funneled as far south as the Gulf Coast. The forecasts are startling: 31 below zero Celsius in Fargo, North Dakota; minus 35 C in International Falls, Minnesota; and 26 below C in Indianapolis and Chicago. At those temperatures, exposed skin can get frostbitten in minutes and hypothermia can quickly set in as wind chills may reach 45.5, 51 or even 56.7 below zero C.