Federal Meteorological Handbook No. 1 - Marrella

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5.1 General CHAPTER 5 WIND Wind shall be measured in terms of velocity, a vector that includes direction and speed. 5.2 Scope This chapter prescribes the standards for observing and reporting wind data. 5.3 Wind Parameters As used in this chapter, wind is the horizontal motion of the air past a given point and includes: a. Direction. The direction, in tens of degrees, from which the wind is blowing. b. Speed. The rate, in knots, at which the wind passes a given point. c. Gusts. The description of the variability of the wind speed. d. Peak wind speed. The maximum instantaneous wind speed measured. e. Wind Shift. A change in wind direction. 5.4 Wind Observing Standards Wind direction, speed, and gusts shall be determined at all stations. All other wind related parameters shall be determined at designated stations. 5.4.1 Wind Direction. The wind direction shall be determined by averaging the direction over a 2-minute period. When the wind direction sensor(s) is out of service, at designated stations, the direction may be estimated by observing the wind cone or tee, movement of twigs, leaves, smoke, etc., or by facing into the wind in an unsheltered area. 5.4.2 Variable Wind Direction. The wind direction may be considered variable if, during the 2-minute evaluation period, the wind speed is 6 knots or less. Also, the wind direction shall be considered variable if, during the 2-minute evaluation period, it varies by 60 degrees or more when the average wind speed is greater than 6 knots. 5.4.3 Wind Speed. The wind speed shall be determined by averaging the speed over a 2-minute period. At designated stations, Table 5-1 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. 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. 5.4.5 Peak Wind Speed. Peak wind data shall be determined with wind speed recorders. The peak wind speed shall be the maximum instantaneous speed measured since the last routine METAR. ��
Table 5-1. Estimating Wind Speed Knots Specification Knots Specification Large branches in motion; whistling
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Federal Meteorological Handbook No. 1 - Marrella

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