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,' ~~_Loca~ ~;~~r~a~ro~ica~ data • Annual Summary With Comparative Data 1975 ALAMOSA, COLORADO ti~~n i ui c~~i P ~~~ ^YF, O P \` ~ „~,~~ c ~~' e Z'~FO STATES OF P~~P` Narrative Climatological Summary Alamosa is located in the south-central part of Colorado and is near the center of the San Luis Valley which lies in a broad depression between mountain ranges converging to the north, and is the first of a series of basins along the Rio Grande River. The mountain ranges to the east reach altitudes over 14,000 feet and those to the west are between 13,000 and 14,000 feet. The length of the valley from north to south is over 80 miles, and its greatest width is about SO miles. The valley floor ranges in alti- tude from 7,500 to near 8,000 feet and has a remarkably flat surface, except for a range of low hills across the southern portion. From the lowest areas which lie along an axis near the eastern border, the valley floor rises to the foothills, steeply to the east and more gently to the west, at first not more than 3 to 6 feet to the mile, but gradually increasing toward the margins of the valley. The climate of the San Luis Valley is marked by cold winters and moderate summers, light precipitation, and much sunshine. At Alamosa about 80 percent of the annual precipitation occurs from April to October, most of it in the form of scattered light showers from thunderstorms that develop over the mountains and move into the valley during the afternoon. More than half of these thunderstorms occur during July and August. Hail frequently falls in some parts of the valley during their movement. Winter snows, which occur mainly in frequent light falls, average less than 40 inches a year, with occasional falls as early as September or as late as May. A good snow cover will remain on the ground for several weeks during the coldest months. The average annual precipitation is below IO inches throughout the valley, dropping to near 6 inches in the central part. All agriculture in the valley is therefore depend- ent on irrigation, using water supplied by the more abundant precipita[ion in the surrounding mountains. Summer grazing of cattle and sheep on nearby mountain ranges and smaller valleys is extensive. The growing season averages about 90 days at Alamosa, increasing to over 100 days in the areas north and west of Alamosa. July and August are usually the only frost free months. A wide variety of vegetables, grains, and feed crops are grown locally, potatoes being the main commercial crop. Summer is characterized by frequent days with maximum temperatures in the middle eighties and minima in the low forties. The highest temperature so far recorded was 93°. Relative humidity runs from an average of 76 percent in the early mornings to around 40 percent during the afternoons. The coolest ever recorded is 50° below zero. Winds are light during the coldest weather but are strong with occasional blowing dust during the spring and early summer months. noaa ATMOSPHERIC ADMINISTDRATION/ DATA SERVECEAL/ NAS E10 LL LrCCIM ATIC CENTER