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Colorado Climate Center -Climate of Colorado Page 5 of 8 May 1935 nearly two feet of rain fell along the Republican River in eastern Colorado causing one of the worst floods in state history. June flash floods in 1965 were also devastating. The weather station at Holly in southeast Colorado measured 18.81" of rainfall in that exUaordinarity wet month. It is more common, however, to be too dry. Annual average precipitation ranges from less than 12 inches in the Arkansas Valley between Pueblo and Las Animas to almost 18 inches in extreme northeastern and southeastern corners of the state. Many years ace drier than average, and some years receive only half or {ess the long-term average. The region seems almost always in or on the verge of drought. Mufti-year drought is common to the area such as the decade-long drought of the 1930s, the severe drought of the mid 1950s and 1970s and the recent intense widespread drought of the early 2000s. At the western edge of the plains and near the foothills of the mountains, there are a number of significant changes in climate. Average wind movement is less, but areas very near the mountains are subject to periodic, severe turbulent winds from the effects of high westerly winds over the mountain barrier. These winds are sometimes referred to as "chinook winds" when they warm, and "bore winds" when they are associated with a strong cold frontal passage downsfope off of the mountains, Temperature changes from day to day are not quite as great; summer temperatures are lower, and winter temperatures are higher. Not surprisingly, this milder corridor close to the mountains is where the majority of Colorado's population now lives. Precipitation, which decreases gradualty from the eastern border to a minimum near the mountains, increases rapidly with the increasing elevation of the foothills and proximity to higher ranges. The decrease in temperature from the eastern boundary westward to the foothills is less than might be expected with increasing altitude. This results from mountain and valley winds and greater frequency of the chinook. Below the Royal Gorge of the Arkansas River, the mountain and valley winds are persistent enough to modify the climate over a considerable area. Descending air currents frequently prevent the stratification of air necessary for the occurrence of excessive cold. As a consequence, the winter climate is milder near Canon City and Penrose than anywhere else in the State. CLIMATE OF MOUNTAINS OF COLORADO Colorado is best known for its mountains. They occupy less of the area of the state than many realize, but they profoundly impact the climate of the entire region. The main feature of the mountainous area of central and western Colorado is the dramatic differences in climate over shoR distances. With elevations ranging from below 7,000 feet in the tower mountain valleys to more than 14,000 feet on the highest peaks, all aspects of the climate are affected: temperature, humidity, precipitation and, of course, wind. In general, temperatures decrease with elevation. Summer afternoon temperatures consistently decrease about 4-5 degrees F per thousand feet. Typical July afternoon temperatures are in the 70s and 80s in the lower valleys but are only in the SOs and 60s in the higher mountains. But elevational temperature changes era often masked by temperature inversions especially at night and during the winter. Cold air is more dense than warmer air and collects in some of the mountain valleys. On clear nights, especially during winter when the ground is snow covered, strong temperature inversions form, Under these circumstances, the coldest temperatures are found near the censer of these high valleys, while temperatures in the high mountains are http://ccc.atmos.colostate.edu/climateofcolorado.php 5/18/2007