Crozet Weather Almanac: The Winds of Spring

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By Heidi Sonen & Roscoe Shaw

March 2015
March 2015

March and April are known for kite flying and lots of wind. That is certainly true here and the reason is vertical mixing of higher momentum air aloft. If that makes no sense to you, then good. You are normal. We will try to explain.

For starters, wind blows because of differences in pressure. Mother Nature tries to even things out so wind always blows from high pressure to low pressure. This happens every time you open a door and feel the air rushing either in or out.

In the atmosphere, winds get complicated by friction with the ground and rotation of the earth. Fortunately, much of this can be calculated by complex mathematical forecast models which now do a very nice job of analyzing and forecasting wind.

In the upper atmosphere, rivers of air flow smooth and fast and free of friction and interference. The closer you get to the ground, the more the flow is distorted by terrain. Friction and temperature differences of the surface make winds at the ground much more complex.

One way that we can get high winds here is to have an unstable atmosphere that can bring high winds from the upper atmosphere to the surface. In the winter, winds aloft are usually strong but the atmosphere is often stable so the high winds stay above us. In the summer, the atmosphere is often unstable, but the winds aloft are generally much weaker. Spring afternoons often combine an unstable atmosphere with high winds aloft and the combination yields plenty of wind.

The spring winds often follow the sun. At night and early morning, the atmosphere is stable and the winds light. But, as the sun heats the ground, the atmosphere destabilizes and faster winds from above reach the surface, leading to those kite flying spring afternoons. In the fall, the sun is much weaker, the atmosphere more stable, and the winds much lighter.

March Recap…

March came in like a lion and left like a lamb just the way it is supposed to. On the first of the month, freezing rain fell and the temperature averaged just 26. On the last day, we jumped to a high of 74 and the grass was growing! Overall, the month was colder than normal but wildly variable, like March usually is. Temperatures ranged from 7 to 79.

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