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<br />10 <br /> <br />1 <br /> <br />i- <br />l- <br />i- <br /> , <br />l- <br />I- <br />l- <br />I- <br />I- <br /> <br />9 <br /> <br />8 <br /> <br />7 <br /> <br />6 <br /> <br /><Il <br />>> <br />8 5 <br />'II: <br /> <br />4 <br /> <br />3 <br /> <br />2 <br /> <br />o <br /> <br />Oct <br /> <br />Nov <br /> <br />Dee <br /> <br />Jan Feb <br />Month <br /> <br />Mar <br /> <br />Apr <br /> <br />May <br /> <br />Figure 3-5. - Average number of days per month with precipitation of 0.1 in <br />or greater at the Blowhard Mountain radar site, <br /> <br />days. Therefore, figure 3-5 would suggest that the typical stonn frequency of 6 to 7 per month, estimated <br />from SLW and other data in section 3.2,1, is not unreasonable but may be slightly optimistic. <br /> <br />Important for consideration of winter seeding operations is the number of days with precipitation versus <br />the percentage of nonnal winter precipitation. Figure 3-6 shows October through May percent of nonnal <br />values (both precipitation and snowfall) for the period of record (remember that the first half of the 1980's <br />is missing). Values range for about 50 to 170 percent of normal. Thus, the maximum season had more <br />than 3 times the precipitation (and snowfall) of the minimum winter. <br /> <br />Figure 3-7 compares the total number of precipitation days per season to the percent of nonnal winter <br />precipitation. There is a definite relationship with a linear correlation coefficient of 0.8. The wettest <br />winters had over 60 days with precipitation while the driest winters had less than 25 days. Hence the <br />frequency of storm passages has a major influence on the seasonal snowpack. A normal winter season <br />had about 45 days with precipitation of 0.1 in or more. <br /> <br />Precipitation is strongly related to elevation. Figure 3-8 shows a comparison of monthly average <br />precipitation for Cedar City, BMR, and Hatch, located upwind of, on top of, and downwind of the <br />mountain barrier, respectively. During most of the winter months the high elevation site received about <br />1.5 to 3 times as much as the lower elevation stations. Also there was very little difference between the <br />two valley sites except in the spring months when C..edar City had higher monthly averages. <br /> <br />The relationship between precipitation and elevation can be seen in figure 3-9 which is a plot of elevation <br />versus the mean water equivalent of the snowpack, as measured on April 1 for the years 1961-85. All <br />available snowcourse data in or very near the Sevier River Basin are included. While considerable scatter <br /> <br />23 <br />