Author Topic: How long does a gust last?  (Read 1415 times)

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Offline DaleReid

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How long does a gust last?
« on: August 06, 2017, 02:25:53 PM »
Reading through some discussions on an ideal wx station and other random thoughts on a beautiful day, I got wondering how long a gust lasts, both scientifically, but also as a general term.

I've had the experience of the first gust of an approaching thunderstorm, with the transition from mild breezes to the sudden wind strength and direction change as the downflow hits before the rain starts.  I've been outside on a windy March day with already strong winds when for a second or two, the wind speed picks up substantially, thrashing the yet-bare tree branches around even harder, even to the point of causing an old standing yet dead tree to loose a big branch or go over entirely.

If we sample the speed of the anemometer for example a second once every 30 seconds, we certainly will miss some of these, and will we really have anything more than a peak wind speed reading?

Other than ultrasonics which can read the wind speed many times a second or a chart recorder with a voltage output wind monitor to  show speeds, how do the station manufacturers determine what a gust is, and how important is it to grab the gust speed other than to  know if a tree goes over, a sign gets bent, or an engineer is designing the wind load for an antenna on a tower and so on?

Just curious.  Now back to watching this nice cloud go by and enjoy the last of some great lemonade.  I guess if there is no certain answer, I'll have to go back to contemplating my navel....

Dale
 
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Offline Bushman

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Re: How long does a gust last?
« Reply #1 on: August 06, 2017, 05:45:25 PM »
https://www.wmo-sat.info/oscar/variables/view/205  Of course the NWS uses a different definition.
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Offline floodcaster

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Re: How long does a gust last?
« Reply #2 on: August 07, 2017, 10:44:04 AM »
From "back in the day" of taking surface observations, here's an excerpt from the FMH-1:

5.4.4 Wind Gust. The wind speed data for the most recent 10 minutes shall be examined to evaluate the occurrence of gusts. Gusts are indicated by rapid fluctuations in wind speed with a variation of 10 knots or more between peaks and lulls. The speed of a gust shall be the maximum instantaneous wind speed.

For ASOS, see section 3.2.2.2 of http://www.nws.noaa.gov/asos/pdfs/aum-toc.pdf

Bill


 

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