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-2- I I I I I I I , ! during the stom. Surface winds reported at the Salt Lake International Airport were out of the northwest behind the front. The canyons in the Wasatch Mountains slope upward to the east, in particular Big and Little Cottonwood Canyona. This, of course, adds upslope lifting to an already unstable airmass, further enhancing the rainfall in these areas. Persons with the City Water Department whocwere in the area at the time commented that the rainfall seemed especially heavy in the vicinity of Storm Mountain in Big Cottonwood Canyon. The upper level flow patterns shown in Figures 6 and 7 help explain why the front was slow moving. Figure 7 shows the upper low digging almost due south through California during the period. This digging resulted in a flow aloft over Utah which was parallel to the front. By Sunday evening (OOZ Monday September 27), the upper low had moved onshore and was located over western Oregon (Figures 7 and 21). The heaviest rainfall, however, was in southwestern Utah along the cold front (Figures 22 and 23). The satellite pictures at this time showed another well-formed band of activity over central Nevada behind the front. This was probably an impulse moving around the south side of the trough as the low continued southeastward. An extensive area of light to moderate rain- fall continued over all of western Utah, however, and added more water to already overflowing streams. On Monday morning the upper low center was over northern Nevada (Figure 24) with at least two smaller impulses rotating around it which would have trajectories over Utah. The surface front (Figure 25) was now located over extreme southern Utah or northern Arizona with steady rainfall continuing behind it. Additional rains were associated with the movement of the upper low through' Utah and fell on already saturated ground. In some locations where the ground is essentially rock, the majority of the water had already been running off from the surface for 12 to 24 hours. Figure 26 shows a distinct banded cloud structure from north to south across the state. This storm, like most, consisted of bands of strong cellular activity which appeared to form over Nevada and then move eastward into Utah. By. Monday evening (Figure 27), the upper low was over' southetn Nevada and southwestern Utah with a full latitude trough extending from the low to the Arctic Circle. This trough continued to move eastward slowly with most of the activity to the northeast of the low (Figures 28 and 29). Additional flooding problems occurred over the north as the low began to open up and dumped another 1.38 inches of rain at the Salt Lake International Airport between 6:00 P.M. Monday and 6:00 A.M. Tuesday.