Why does hot water instantly turn into steam in subzero temps?
Temperatures have plummeted across parts of the Lower 48. Some 87 million people are facing subzero temperatures this week as the polar vortex slides south. Factoring in the wind, it feels like it is almost 60 degrees below zero in some places.
People in the Twin Cities woke up to wind chills of more than 50 degrees below zero Wednesday morning. While most would probably take that kind of cold as a sign to stay inside, others take to the great outdoors for a little science fun. After some convincing, my parents braved the crisp Midwest air of the polar vortex to shoot this video. It's a cup of boiling hot water instantly turning to steam as my dad tosses it into the air.
At the time this video was shot, the air temperature was close to 20 degrees below zero! The dew point was even colder, a lip-cracking 31 degrees below zero. The cold, dry air is what allows this unique weather phenomena to occur.
It's more about how dry the cold air is than the cold air itself. The cold helps, because an arctic air mass like the one gripping much of the Lower 48 is typically extremely dry, so the water can evaporate and condense much faster.
Some videos say the water is turning to snow, but that is misleading. Boiling water is already close to evaporating. Think of the steam that rises from the pot before you dump in the noodles. It's like that, but on both a much smaller and a much larger scale all at once. Tossing the hot water in the air increases its surface area, meaning more of the hot water touches the cold, dry air.
This allows it to evaporate much faster, and since the air is so cold and dry, the water almost instantly evaporates into vapor, condenses into a cloud and drifts off.
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