| OCR Text |
Show This factor decreases the orographic lifting effect of the wind as it becomes more and more parallel to the mountain range until VQ becomes nil for wind directions of 360° or 180 . For wind directions with any easterly component, orographic lifting is considered to be small, and for computational purposes a value of V0= 5 mph is assumed. From topographic charts of the Alta area, VH was approximated as 0.095 » The available moisture, or precipitable water may be obtained by the standard equation P W = - _/° q dp ( 3) CJ " H This value may be conveniently obtained by use of a plastic overlay ( developed by the Weather Bureau) used in conjunction with the Stuve d iagram. Harley ( 1965) developed a tabular method of computing precipitation rates using the computed vertical velocity and precipitable water. See Table 1. His method is used in this study to compute the precipitation rate which is orographically induced. This accounts for most of the precipitation at Alta. During each storm period, the topographically induced vertical velocity and precipitable water were computed for each 12 hourly sounding taken at the Salt Lake City Airport, and interpolation was used to obtain the intermediate data at the 6 hourly intervals. Using the Harley method, precipitation rates were computed ( in units of inches/ 6 hours) and combined with the duration of snowfall to give a 24- hour precipitation computation. A 24- hour period was used since precipitation data for Alta is only given for that interval of time. The results are shown |
