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Treebeard's Stumper Answer
27 Feb 98

The Rain and the Wind

We've had lots of opportunity to be weather watchers this month! I've noticed that the first sign of an approaching storm is often a change in the wind. Our usual afternoon wind at school is a north or west wind that blows up the Valley from the ocean. But before and during a storm the wind usually blows down the Valley from the south or east. Just look how many of the hundreds of downed trees lie pointing northwest. Our winter storms come from the north, even with El Niño. So why do the wind and rain come from the south?

Note: Our part of Central California has been slammed by one storm after another this month. We had two feet of rain in one week at my house in the mountains behind Santa Barbara! This stumper is about our storms, but I think an East Coast nor'easter raises the same question: the storm moves up the Atlantic coast from the south, but the wind and rain come off the ocean from the northeast. Why?


Here in Central California, our winter storms begin as areas of low pressure that form over the Pacific Ocean. Less pressure means less air, so a new storm pulls air in towards the center like a drain, creating wind. Because the earth turns, the air mass moves west and begins to rotate counter-clockwise. (Opposite in the Southern Hemisphere.) This produces the classic comma-shaped spiral storm that we've all seen in satellite images. The spiral is moist air being pulled in from the south, bringing rain with it. Our winter storms do come from the north, but the wind and rain come from the south, especially this year!

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Copyright © 1998 by Marc Kummel / mkummel@rain.org