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<br />Average annual precipitation varies from more than 50 <br /> <br />inches in the higher reaches of the Basin to less than 10 <br /> <br />inches in the lower valleys. Average annual snowfall varies <br /> <br />from more than 400 inches in the higher elevation to approxi- <br /> <br />mately 20 inches in the Grand Junction area. The higher <br /> <br />valleys have an annual frost-free period of fewer thatn 40 <br /> <br />days, while the lower valleys average about 190 days. <br /> <br />Seasonal distribution of precipitation is fairly uniform. <br /> <br />Slightly less than half usually occurs during the December- <br /> <br />April period in the form of snow. About one-third usually <br /> <br />occurs during the growing season, though this is variable with <br /> <br />respect to location. The accumulation of winter snow. supplies <br /> <br />the streams and is the basic source of the surface water <br /> <br />,~i~source. Some rainfall generally takes the form of showers <br />~"" <br />that are highly variable and contribute much less to the over- <br /> <br />all water supplies. Rainfall is typically mountain thunder- <br /> <br />shower in characteristicts, with only limited areas having <br /> <br />locally severe intensities. <br /> <br />Annaul evaporation ranges from about 60 inches near Grand <br /> <br />Junction to about 20 inches in the higher mountains. Tempera- <br /> <br />tures range from 'occasional periods of above 1000 F in the <br /> <br />Grand Junction area to winter temperatures of about 500 F <br /> <br />below zero in the high mountaiDs. <br /> <br />3 <br />