Politics, Weather, Photography, and the Dog
Monday 10 March 2014

It looks like we're going to go 71 days with snow on the ground before it all melts. But a couple of subtle yet telling things have happened since I last griped.

First, the temperature has gone up since sunset, as forecast. It hasn't gone up a lot, but the influx of warm air from the Gulf of Mexico will continue through tomorrow, to the detriment of all the snowdrifts in Chicago.

It's hard to get your mind around how much heat the atmosphere moves around. A human being can generate about 6-8 megajoules as heat every day. (A food calorie is about 4,200 joules.) Your car or office can generate tens of megajoules to keep you warm. But when an air mass comes up along the Mississippi to Chicago, it's dragging so much energy that we need to review exponents. We're talking about petajoules.

Which brings up the second point. We're not talking about an inch of fluffy ice crystals on a flower. We're actually talking about megatons of ice covering...everything. Not snow; ice.

Take a 10m square of ice just 50 mm thick—meaning just about any square of lawn in the Chicago area right now. So, that's 100 square meters times 50 mm (0.05m), which yields just 5 cubic meters of ice. It turns out, to change just that small amount of ice—oh, wait, that's five tons of ice (do the math)—into water takes 16.5 gigajoules of energy.

Also, when the energy goes into melting ice, it doesn't go anywhere else. I'll hold off on the physics for the moment, except to say that energy can't be created or destroyed, so when it goes into changing the state of a large mass of water without changing its temperature, it's pretty much unavailable for anything else. (Physicists reading this, please be kind; it's close enough.)

This is just a long way of saying: those last millimeters won't go quietly. The last bits of "snow" that the official weather observers measure aren't really snow, they're ice; and ice takes a lot of heat to melt. (Snow is easier to melt because it has so little mass for the same volume.)

Still, if the temperature gets up to its predicted 14°C tomorrow, that's a lot of heat fighting a lot of ice. It might get rid of the official snow cover at the airport, even. And that would leave us with nothing more than the two-meter snowbanks pushed up by all the plows for the last ten weeks. Joy.

Sunday 9 March 2014 22:33:11 CDT (UTC-05:00)  |  | Chicago | Weather#
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David Braverman is a software developer in Chicago, and the creator of Weather Now. Parker is the most adorable dog on the planet, 80% of the time.
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