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. ( CLIMATOLOGY I- - 7. GENERAL. Wide variations of climate occur in the Arksnsas River subbasin above John Martin Dam. In the moun- tainous regions of the headwaters, precipitation varies widely over relatively short distances. It ranges from 10 inches annually in some locations to 40 inches annually over limited areas at the crests of some mountain ranges and peaks. Much of the total precipitation at the higher elevations is in the form of snow. Runoff from this snow is at a maximum in the late spring and early summer months, and constitutes the dependable water supply for the subbasin. In the plains region most of the precipitation is in the form of rainfall which occurs intermittently and at irregular intervals. At times, rainfall in the form of violent thunderstorma causes flash floods of short duration and small volume but of damaging intensities. More than 80 percent of the average annual precipitation on the plains occurs during the period April through October. Mete- orological stations and types of data gathered at these stations are shown on Plate 2. . . . I .8. PRECIPITATION. Annual precipitation normals within the subbasin vary from 24.27 inches at Lake Moraine to 9.69 inches at Buena Vista. At Lake Moraine 76 percent of the annual precipitation occurs during the 6 month period April through September, and at Buena Vista 68 percent occurs during this period. The peak rainfall months throughout most of the sub- basin are May and July. Peak thunderstorm activity is reached in July with an average of 17 thunderstorm days at Colorado Springs and 13 at Pueblo. A maximum 24-hour or maximum observed day precipitation of 6.10 inches occurred at Rye in May 1955. A maximum 24-hour precipitation amount of 3.77 inches occurred at Pueblo in October 1957. A maximum monthly snowfall of 29.3 inchea and a maximum 24-hour amount of 16.8 inchea have been recorded at Pueblo. . I ( 9. TEMPERATURE. There is a wide variation of temperature in the Arkansas River subbasin above John Martin Dam. This is principally due to altitude. Leadville. at elevation 10,177 feet, haa mean annual maximum and minimum temperatures of 49.5 and 22.0 degrees Fahrenheit. Las Animas, at elevation 3,891 feet, has mean annual maximum and minimum temperatures of 70.7 and 35.2 degrees. Recorded extreme temperatures have ranged from 114 degrees at Las Animas to -54 degrees at Westcliffe, elevation 7,860 feet. The average last spring occurrence of temperatures as low as 32 degrees varies from April 28 at Pueblo Weather Bureau Airport to June 24 at Lake Moraine. The average firat fall occurrences at the same locations are October 12 . . I - 3 .