Upper Colorado Region Comprehensive Framework Study: Appendix V, Water Resources

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PART III CLIMATE The climate of most of the region is semiarid to arid and is predominately a four season climate. Wide variations in precipitation, temperature and wind movement occur primarily as a result of varied topography and to a lesser extent the rather wide range in latitude. Predominately, the climate is associated with Pacific Ocean air masses which move inland from the west, carrying much of the region's precipitation. Seasonal influences include summer cyclonic thunder- storms that sweep into the southern portion from the Gulf of Mexico and occasional Canadian arctic air that extends into the northern portion during the winter months. Precipitation Precipitation is affected by two major factors, the moisture supply and the topography of the area. Since the region is several hundred miles from major sources of moisture and the air masses cross several mountain ranges before reaching the region, precipitation is limited for all except the high mountain areas. Average annual pre- cipitation ranges from less than 6 inches in the lowest valleys to more than 50 inches in the higher mountains. Average precipitation in most valleys and agricultural areas ranges from about 8 to 16 inches per year. Precipitation in amounts over .10 inch per day occur on an average of about 10 to 50 days per year, depending primarily on elevation and altitude. Intensities vary widely but seldom exceed 4.0 inches in 24 hours. Distribution of precipitation through the year shows a less distinct seasonal pattern than occurs in many other western regions. Precipitation is heaviest during the winter and spring months. An exception occurs in the southern portion where maximum monthly precipi- tation often, occurs from the July, August, and September thunderstorms. Precipitation during the late October through mid-April period is dominated by snow, particularly at higher elevations. Annual snowfall ranges from 200 to 300 inches in the higher mountains down to about 5 inches in the lower valley and plateau areas. Maximum snow accumula- tion occasionally exceeds 100 inches in the higher areas and does not completely melt until late summer. 10