Brainstorm Answer: Freezing Water |
 Dave Thurlow, Host |
What if you took a glass of water and set it outside when the temperature is just above freezing, say 34 degrees Fahrenheit. Is there any way that the water could freeze? Hi, I'm Dave Thurlow from the Mount Washington Observatory and that was the question I posed to you on a recent Weather Notebook Brainstorm. Could water freeze at a temperature above freezing?
David Horsley from Amarillo, TX, a listener of KACV-FM, like so many of the folks who responded, thought that wind chill might provide enough cooling to chill water in a glass to the freezing point. But it can't do that. Wind can quickly rob heat from anything it blows by it can't make any object have less heat than it does. However, David came up with another possible circumstance.
David: "The second might be in a situation in which radiational cooling occurred even though the air temperature was 34 from the cooling of the atmosphere at night."
Now this radiational cooling is a more likely process but it would call for the glass water to be completely inulated from the ground, high above any other objects, there'd have to be no wind at all, and the night would have to last for more than 12 hours. The water could then loose heat to space faster than the air does. One way that is sure to work has to do with changing air pressure. Mark Beyer, a WXEL listener in West Palm Beach was on the right track.
Mark: "I would think that if you were in Denver and there was less air pressure the water would freeze if it wasn't colder than 32 degrees."
Actually, you'd have to be out in the stratosphere somewhere for the temperature to be below 32 and to have the air pressure down to next to nothing. There, or in a vacuum chamber, water will actually boil until it freezes.
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