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IV. CLIMATIC FACTORS AND HYDROLOGY t( Go Weather of 1991-199' During the "winter" portion (November - March) of the winter of 1994-95, Pacific and Arctic storm tracks provided the Colorado mountains with generally mild weather. Typical winter storms from the Pacific area moved infrequently across the southern and central Colorado mountains, causing a less than average snowpack to accumulate. Meanwhile, the central and northern mountains and the eastern high plains received little snow accumulation from Arctic storms from Canada and Alaska. Then in April, particularly beginning in the middle of the month, it began snowing frequently in the mountains and along the Front Range. A series of persistent storms (snow and/or rain) began to occur with regularity. These storms deposited healthy accumulations of snow (and/or rain) every 4-5 days somewhere across the state. The storms lasted almost through the second week of June. As the snowpack rose, the moisture content of the snow rose faster, since spring snowstorms are characteristically "wetter" than winter storms. The U.S.D.A. Natural Resources Conservation Service (NRCS) monitors snowpack in Colorado's mountain watershed through a network that includes automated sites and sites that require manual recording. At the beginning of each winter month the manual sites are visited and statewide and basinwide snowpack figures are computed. On April I, 1995 the statewide and basinwide figures (the percent of the 20-year average) were low to slightly above normal, as shown below Table 1 Location Percent of Average April 1 May 1 June 1 June 15 South Platte River Basin 77 122 374 657 Arkansas River Basin 112 183 338 628 Rio Grande Basin 126 167 257 367 Upper Colorado River Basin 106 132 304 413 Gunnison River Basin 125 161 481 991 Southwestern Colorado 125 159 334 405 The April I st figures were not indicative of an impending snowmelt flood threat in any of the state's major watersheds. Then, approximately midway through April, things changed. The dry and mild weather that had prevailed through much of the winter was replaced by wetter and cooler weather. When the May I, 1995 figures were calculated, there had been a considerable change. In fact, the increase in the basin figures from April I to May 1 led directly to the creation of the Flood Task Force and subsequently to all of the other preparatory measures taken by federal, state and local agencies and by private entities.