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Treebeard's Stumper Answer
6 March 2000

We had snow at my house on San Marcos Pass on Monday, March 6. Snow Day! I noticed this stumper as the snow melted from our cars. This may be commonplace elsewhere in the country, but it seemed too unusual here in Santa Barbara to offer as a regular school stumper. This is a bonus stumper for everyone else.

Snow on the Hood

We had 3 inches of snow early this morning! That's unusual here in the mountains behind Santa Barbara, though we had another March snow storm last year. The snow started to melt away as the storm cleared. I noticed that on each of our cars, the snow on the flat hood over the engine melted first. Hours later, the tops and trunks of our cars were still covered. Why did the snow melt so much faster on the hoods? None of our cars had been driven for at least a full day before.

Early morning. The snow is already starting to melt
from the hood of our Volvo wagon on the right.
 
Later in the morning. The hood of my little Chevy is
completely clear, but the rest is still covered. Why?


I'm sure the snow melted from the car hood first because the massive engine block beneath takes longer to cool than the air inside the passenger compartment and trunk. It was barely freezing when the snow started, so the engine block didn't have time to reach freezing temperature. Look close at the top picture. The snow is slipping from the hood in a sheet because it's thawing from beneath. In colder climates, I would expect the opposite effect. Snow would stay on the hood longer, since it would take longer for the engine block to warm up during a thaw.

Notes:

The snow melts from the car hood for the same reason that lakes don't freeze with first snow, most of winter comes after the winter solstice, and drinks stay cold after you take them from the cooler. It has to do with heat capacity.

We had another March snow storm last year that dropped much more snow and damaged our oak forest. (See Storm Damage (26 March 1999)). What is it about March snow in central California? Is this an unexpected part of our current La Niña weather pattern? Or are February and March coldest just like August and September are usually warmest?

Snow is uncommon and exciting here in the mountains behind Santa Barbara, but we get lots of frost and an occasional hard freeze. Here's a few more frost stumpers I've noticed:

Melting snow is a real engineering problem in much of the country. Tesmar Application Technology has an interesting tutorial on Practical Snow Melt Design and why it's difficult.

We've had interesting weather here in central California for the last few years! Here are a few more stumpers about our local weather and natural history: California Hurricane (24 Sep 99), Storm Damage (26 Mar 99), Scarcity and Abundance (22 May 98), Pastures of Plenty (10 Apr 98), The Rain and the Wind (27 Feb 98), Fall or Spring? (21 Nov 97), Cold Winter Sun (6 Dec 96), and Winter Question (15 Nov 96).

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Copyright © 2000 by Marc Kummel / mkummel@rain.org