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IV. DESCRIPTION OF THE FLOODS OF JUNE 1965 16. METEOROLOGY During the period of 15-18 June 1965, a quasi-stationary front was oriented on a north-south line along the mountains in southern Wyoming, Colorado, and northern New Mexico. On 14 June, a closed circulation formed aloft over the California-Nevada area and continued to deepen, thereby causing southerly winds over Colorado. This upper air low, coupled with a ridge over the Great Plains region, produced an atmospheric circulation that transported a deep layer of moist air northward frOm the Gulf of Mexico to the plains east of the Rocky Mountains. At the same time, a series of squall lines formed and moved rapidly eastward from the quasi-stationary front, triggering intense precipitation in various locations east of the mountains. The surface dewpoint temperatures during this period were generally in the upper 50's. On 18-19 June the upper air low began dissipating, allowing the upper-air wind circulation to return to a more westerly direction over Colorado. The quasi-stationary front then began to move eastward out of the flood area as a cold front. 17. DEPTH-AREA-DURATION VALUES The rainfall isohyetal map of the storm, plate 2, and the rainfall depth-area curves, plate 3, illustrate that the storm of 16-17 June 1965 ranks with the major storms for this general area. The isohyetal map and pertinent depth-area values were derived from the regular Weather Bureau precipitation station records for this area, and from "bucket survey" data obtained shortly after the storm by survey tesms from the Corps of Engineers and the Bureau of Reclamation. Plate 4 illustrates the 6-hour storm depth-area amounts on 16 and 17 June for the portion of,the storm in the Denver-Colorado Springs area and, for comparison, the 6-hour' probable maximum storm values and the 6-hour values for the 30-31 M~ 1935 storm. Relative storm magnitudes are self-evident. c 18. STORM PATTERNS Antecedent rainfall prior to the principal storm was moderate and spotty. The floods ,which occurred in the South Platte River basin during the period 14-22 June 1965, resulted from heavy to torrential ra.infa.ll over large portions of the South Pla.tte River basin. Heavy rainfall occurred over portions of the northern sections of the South Pla.tte River basin on the 14th and 15th of June. As the storm system moved southward, torrential rainfall centered principally over the Plum Creek 'and Bijou Creek watersheds on 16 June. Storm rainfall on 16 June extended over some 3,000 square miles of the South Platte River basin, including the Plum Creek, Cherry Creek, and Sand and Toll Gate Creek watersheds in the Denver region, and the Kiowa Creek, Commanche Creek, Badger Creek, and Beaver Creek watersheds to the east. 10