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OG:J488 Mountains. Thus, at lower elevations, little or no precipitation Is received during the winter months, while at the very high elevations cloudiness and light snow are very frequent. In a few rare instan. ee5, the large c)'clonic storm can move into North America in the period between December and March to the south of the high Sierras. Such storms can carry large amounts of moisture toward the north- east through the relatively low terrain across the desert. This moisture is then subsequt-ntly pre- cipitated i.nto the upper basin areas in large amounts, At the end of the winter period. primarily in April and 1>lay. there is a storm tendency for cy- clonic storms to be generated over the State of Arizona. and their movement is relatively slow during the formative sta.o:-e. These storms pull in air which has originally moved over ~ew Mexico o. --- -.. --. . - - --, '" I I ["' ~~--y-.. _ c~ - - ~p ~ 1ft 'tel"l -", ..?.....'It.r C "" ....~ , --....... "'" " "IilIoo' . , .- ~'- ! ""I "I If " '~, -1~, '~.' ..... 1)\' -<... tt.1\ '~;'f-~'" , ' ~ ~} .-(. ....."" 'V'" _., ~, ' ~ , "t .r__~ , ",'';:' . . ~ .f" - - , ,. . - ~ \ ., from the Gulf of Mexico. As these storms move to the northeast across the state of Colorado, heavy moisture deposits are deUvered to the eastern slopes, and some precipitation Is moved Into the northern portion of the upper basin area from a trajectory moving around the cyclone and into the basin from the northeast. It is quite unfortunate that this precipitation process is U~ mited to less than 36 hours, since the cyclonic: storm is moving toward the northeast at a rather rapid rate. D. CONCLUSIONS FRO" STUDY OF MOISTCRE SOURCES t. Moisturf" from the Pacific in the winter- time is reliable in producing some snowpack in higher elevations every year. -- --.. ----- , / . , \- I I I ---.....L-~_.- r'- -. I I I I . - ~.- I ~. \. , I - f Fig. H, Source Regions fOr predpiUl.tion in the Upper Colorado River Basin.