How cold is it today in the Midwest? Cold enough that when meteorologist Eric Holthaus tossed a pot of boiling water into the air outside his home in Viroqua, Wisconsin, this happened:
To be precise, the temperature at the time was minus 21, with a wind chill of minus 51. Wisconsin is part of a huge swath of the United States that is seeing its coldest weather in decades today, thanks to an Arctic air mass barrelling down from the north. The Weather Channel describes it as "life-threatening cold," with temperatures hitting minus 31 in North Dakota and northern Minnesota.
Holthaus isn't the first to perform the boiling-water-to-snow trick. But he told me it was his first time attempting it—he just moved to Wisconsin from Arizona four months ago. "I didn't expect it to work, actually," he said.
You might think that boiling water would be harder to instantly freeze than a pot of cold water. In fact, Holthaus tried cold water immediately afterward, and it stayed in liquid form. It's the gradient between the hot water and the freezing air that makes the trick work, climatologist Mark Seeley explained in a 2011 LiveScience explainer on the phenomenon. The boiling water has relatively low viscosity, so when you throw it into the air, it breaks into tiny droplets that vaporize almost instantly due to their high ratio of surface area to volume. But cold air can't hold much water vapor, so it quickly clings to tiny sodium or calcium particles and crystallizes.
Similar science—and even more frigid air—is at work in another recent video, which shows what happens when you try to shoot water from a Super Soaker in minus-41-degree weather in South Porcupine, Ontario. (The inevitable clever comment: Geez, how cold is it in North Porcupine?)
One other fun fact about today's extreme weather in the United States: While much of the country is seeing 20-year lows, parts of California are enjoying record high temperatures. And it's 83 degrees in Miami as I write this.
Previously in Slate:
TODAY IN SLATE
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