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May and July rank as the next two driest months. Using NOAA criteria for "wet <br />months", i.e., [he frequency of receiving greater than 2.0 inches over a 44 <br />year period, October and then May have been "wet" more than the other months. <br />August ranks as [he third wettest month. <br />Rowever, if the NWS total precipitation data (1936-1979) is used to establish <br />a 44 year arithmetic mean, then the "driest" months are February, January, <br />July and November respectively. Likewise the "wettest" months are May, April, <br />August, and October in order of diminishing precipitation received (Table <br />2.1-7). <br />Precipitation in [he surrounding vicinity varies considerably with elevation <br />and exposure (orographic effects). Generally, precipitation tends to decrease <br />westward from Craig, particularly at lower elevations. Amounts of precipita- <br />tion are greater in the higher elevations to the east, [o [he south and to the <br />northeast, reaching a total of 20 to 30 inches or more annually in the moun- <br />tain ranges within a 50 mile radius of the proposed mine plan area. <br />• Snowfall in the region delivers between one-third and one-half of the total <br />annual precipitation and is the principal source of stream flow in northwest <br />Colorado (Table 2.1-8 ). <br />Snowfall (snow and sleet) averages 66.5 inches (168.91 cm) in Craig (Berry, <br />1966) and usually ranges from 33 to 77 inches (83.8 to 195.6 cm). Because <br />mountain precipitation is significantly heavier in the winter than in the sum- <br />mer, snowfall is the most significant factor in providing an adequate year <br />round water supply to the lower and drier areas. <br />• <br />2-14 <br />