OCR Text |
Show 39 similar dry period, commonly called " Indian Summer," occurs in September, following the summer thunderstorms and preceding the frontal and Nevada low activity of the fall and early winter. Average annual precipitation ranges from 5 to 15 inches over the Lake to almost 60 inches per year in the higher Wasatch Mountains east of Salt Lake City, Utah. Humidity Few continuing humidity measurements are available in the Basin, but averages from the Salt Lake City Airport can be considered indicative of those in the Great Basin. Humidities at 5: 00 p. m. range from an average of 73 percent in December to 18 percent during July. The average daily range during December is small ( 81 percent at 5: 00 a. m. to 73 percent at 5: 00 p. m.). In July, the driest month, the average 5: 00 a. m. humidity is 49 percent as compared to 5: 00 p. m. humidity of 18 percent. Extremes in relative humidity range from 100 percent during fog conditions in winter to as low as 4 to 5 percent on some hot summer afternoons. The effect of the Lake on humidity has not been completely determined but preliminary measurements have indicated somewhat higher average humidity at the north end of the Lake when the prevailing wind is from the south. Wind Winds in the Basin show extreme variability near the surface primarily as a result of the topography. Over the flat area of the Basin, the pressure gradient determines the direction of the wind. In most of these areas, the prevailing wind direction is from the south. Near the mountains, drainage winds are superimposed upon prevailing pressure gradient winds. With the weak pressure gradients which occur during the summer and |