Sunday, August 30, 2009

Judging wind direction and velocity

I was flying the Twin Comanche into ALX (Alex City, AL) the other day. The AWOS was on the fritz, and there are no other nearby airports with weather reporting. I flew over a nearby lake which gave me the exact wind direction and a decent estimation of the velocity.
Basically, the water on the windward side of the lake is glassy while the other side of the lake has increasing waves going up to the shore. Judging velocity takes a little more experience and depends on the fetch, which is the length of the lake from the windward shore to the leeward shore.

The waves increase from the windward side to the leeward side. Glassy water indicates winds less than 3 mph. Small ripples indicate 3-7mph. Medium waves without white caps indicate 7-10 mph. Some white caps indicate wind less than 15mph. Lots of white caps indicate more. All of this is for a fetch of about a mile in length.

Using bodies of water for your wind indication can be done at altitude and does not require a low pass over the airport to see a tiny windsock. In addition, the water is not likely to be affected by hangars and other airport structures as many windsocks are.

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