Dear Kid,
It occurred to me that someday you might be in a situation where you need to know the speed of the wind and not have a wind-speed measuring device handy.
This is not a subject we spent a lot of time on when you were a tot. You were much more interested in learning to rollerblade and search for bad guys than in learning about wind.
At the time, I rationalized that it was a temporary oversight and we’d get to weather and wind speed study later, but somehow “later” never arrived. And here you are in college without a wind-speed measuring device and you have next to no idea how to figure out wind speed and obviously this is a huge hole in your education.
Therefore (and ergo), let us begin. You may want to take notes.
Observation is the key to understanding wind speed. For example, if the smoke from your campfire rises straight up, the leaves on the trees aren’t moving, and your mother is desperately searching for a fan because “there is no AIR,” it’s a good bet that there is very little wind (under 2 mph).
On the other hand, if houses are flying around in the air, you can be relatively certain that the wind is breaking the speed limit and it’s a good time to be underground lest you wind up with a pair of ruby slippers on your feet. (If you’re wondering how the ruby slippers would be big enough, the answer is “magic.”)
Estimating wind speed between “Can someone please find some AIR” and “Take cover!!!” can be a little trickier. But there are several methods which I shall now explain (you’re welcome).
The first is the Applied Mathematics (because I like saying Applied Mathematics) Military Flag Method.
First find a flag that is hanging in the wind. If you don’t have a flag handy, this doesn’t work at all. And it needs to be a regular size flag. The little ones we got at the Memorial Day parades don’t count. Neither do the banners people hang on their doors to indicate the specific football team they live for.
Now that you’ve found the flag, look at it. Estimate the angle between the bottom of the flag and the flag pole. Divide the angle by 4. The result is wind speed in miles per hour.
Fascinating, no?
However, sometimes we find ourselves in situations without a handy flag. Enter the Beaufort Method.
Sir Francis Beaufort was an admiral in the British Navy. To the best of my knowledge he was never the subject of a Gilbert and Sullivan operetta, and since he didn’t have to go around singing patter songs, he had plenty of time to think about wind.
Here are his rules:
- If the flag is not moving at all, the wind speed is below 11 mph.
- If it flaps lightly and sporadically the wind is blowing at around 12 to 18 mph.
- If the flag is flapping over the whole length of the flag, it is blowing at around 19 to 24 mph.
- If the flag is partially extended and flaps quickly, the wind speed is 25 to 31 mph. A fully extended flag flapping hard in the wind means wind speed is around 32 to 37 mph.
Now you know.
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