Wind Direction and Velocity PDF

200 / CHAPTER 4 Qualimetrics, Inc. Figure 4–4. A digital wind direction and velocity Figure 4–5. An analog wind direction and velocity indicator. indicator. Wind Dir...

200 / CHAPTER 4 Qualimetrics, Inc. Figure 4–4. A digital wind direction and velocity Figure 4–5. An analog wind direction and velocity indicator. indicator. Wind Direction and Velocity Wind direction at airports is always determined in reference to magnetic north and indicates the direction that the wind is blowing from. The direction is always rounded off to the nearest 10°. Thus, a wind blowing from north to south is a 360° wind; a wind from the east is a 90° wind. The international standard for measuring wind velocity requires that wind speeds be measured in knots; 1 knot equals approximately 1.15 miles per hour. Wind direction and velocity information is always preceded by the word “wind,” with each digit of the wind direction enunciated individually. The wind direction is then followed by the word “at” and the wind velocity in knots, with each digit enunciated individually. If the wind measurement devices (see Figures 4–4 and 4–5) are inoperative, the wind speed and direction are preceded by the word “estimated.” If the wind direction is constantly changing, the word “vari- able” is suffixed to the average wind direction. If the wind velocity is constantly changing, the word “gusts” and the peak speed are suffixed to the wind speed. Here are some examples: Wind Direction Wind Speed Pronunciation From the north 15 knots Wind three six zero at one five From the east 10 knots with Wind zero niner zero at one occasional gusts zero gusts to two five to 25 knots Variable from 12 knots with Wind one five zero variable at the southeast occasional gusts one two gusts to three five to 35 knots