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The relative frequency of wind speed intervals versus wind direction for the <br />six stability classes represented near Craig are presented in the Appendix C <br />Climatology, Tables C-1 through C-6. <br />For all the stability conditions sampled, average wind speeds over 8 mph (7.0 <br />knots) occurred only with winds from a southerly direction. .Five of these <br />classes (Classes 1-5) had the highest average wind speeds from the south <br />through the southwestern vectors. <br />Wind speeds over 17.5 mph (15.2 knots) occurred in all six stability classes <br />but usually transpired in conjunction with winds from the south-southwest <br />quadrant. During stability class 3 (transitional conditions) a minor number <br />of wind speeds over 17.5 mph (15.2 knots) occurred from the west-northwest <br />through the north vectors. <br />Table 2.1-11 shows the average wind speeds - maximum, minimum and overall <br />average; the frequency of occurrence for calm periods; the percent of wind <br />speeds less than 10 mph (8.7 knots), wind speeds equal to or greater than 20 <br />mph (17.4 knots), wind speeds equal [o or greater than 30 mph (26.1 knots); <br />and the maximum range of wind speeds (mph) during the 1975-1976 field stud- <br />ies. <br />Mean surface wind speeds above 8 mph (7.0 knots) will occur between 12:00-7:30 <br />pm (MST) as is typical of the afternoon hours and neutral stability condi- <br />tions. This amounts to an approximate hour lag from the mesoscale wind speeds <br />at 200 feet above ground level and is 2 hours earlier than the average meso- <br />acale wind speed decrease. At all hours of the day the average wind speeds <br />will be greater as the elevation above the ground surface increases. The max- <br />imum differences between the 20' and 200' levels at site C2 were 1.5 to 2 mph <br />(1.3 to 1.1 knots) at nigh[ and over 3 mph (2.6 knots) during [he afternoon. <br />• <br />2-36 <br />