PERMFILE104987

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Local Clim~ological Data ~ ~~~"T °F`°M
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Annual Summary With Comparative Data o ~-
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1983 ~ -
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ALAMOSA, COLORADO S>q>ES °F 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 Crande River. The
mountain ranges [o 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 abnut 50 miles. The valley floor ranges in alti-
tude from 7,500 to near 8,000 fee[ 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, et first not more than 3 [0 6 feet
[o tlTe mile, but gradually increasing Coward the margins of the valley.
The climate of the San Luis Valley is marked by cold winters and moderate summers,
liglTt precipitation, and much sunshine. A[ Alamosa about 80 percent of the annual
precipi.[ation occurs from P.pril 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. A`,ore than half of these thunderstorms occur during July and
August. Hail frequently falls in some parts of the valley during their movement.
1Ji nter 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 [he ground for several weeks during the coldest months.
The average annual precipitation is below 10 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 precipitation 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.
j 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°. P.elative humidity runs from an average of 76 percent in the early mornings to
around 40 percent during tt~e afternoons. The coolest ever recorded is 50° below zero.
4linds are light during the coldest weather but are strong with occasional blowing dust
during the spring and early summer months.
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