Question:I read your web page about the Beaufort Wind Scale, and I have one additional question. Are the associated velocities of the Beaufort Scale fastest mile, averaged over 1 minute, 3 second, or 10 minute, or some other standard?
Answer:According to the Smithsonian Meteorological Tables (1966 edition), the Beaufort wind scale relates to the mean wind at 10 m as adopted by the 1946 Paris resolution of the International Meteorological Committee. The Smithsonian Table does not say what the averaging period is but I would assume it is the standard 10-minute mean.
According to the latest US Federal Meteorological Handbook No. 1: CHAPTER 5--WIND, "The wind speed shall be determined by averaging the speed over a 2-minute period. At designated stations, Table 5-1 [the Beaufort Scale for estimating wind speed from tree motion] shall be used to estimate wind speeds when instruments are out of service, or the wind speed is below the starting speed of the anemometer in use."
I take that to mean that the observer watches the trees blow for about 2 minutes (for consistency with other observations) and then estimates the wind speed using the Beaufort land scale.
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