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112 This echo line indicates convergence in the lee side trough located just north of Mt. Harris and explains the observed local backing of Mt. Harris upper winds as compared to the large scale flow. It also yields valuable clues as to the cause of the observed variation of target area"precipitation patterns with Mt. Harris wind direction, since Mt. Harris upper winds are observed to veer more northerly with the southward passage of the sistent east-west line echo. The ratio of Rabbit Ears Pass to Buffalo precipitation rate has been found to be positively correlated with wind tion (measured in azimuthal degrees). Figure 70 gives a measure of the departure of Mt. Harris 10,000 ft. MSL wind direction from the synoptic scale direction, with qualitative explana- tions therefor. Inserting the observed average direction difference for northwesterly flow into the divergence equation, and assuming uniform streamline divergence to be present from the surface (7400 ft. MSL) to 10,000 ft. MSL, a vertical velocity of ~ 10 crn sec-1 was calculated for 10;-000 ft. MSL near the lee-side trough. This vertical velocity is between 10% and 30% of the magnitude of the general or'ographic vertical velocity field across the Park Range. Thus, the presence of a superimposed east-west line of zone precipitation on the general orographic precipitation pattern can be justified on the basis" of comparative vertical velocity values. 3. 3.4 Dependence of Precipitation Patterns on Synoptic Scale 700 mb Wind Direction One of the major problems in selecting cont!:..ol stations for weather cation operations in mountainous terrain is the fact that the meso of precipitation in such terrain is so highly wind direction dependent. This wind direction dependence arises from complex interactions of differing orographic effects due to variations in terrain barrier orientations. A study of these effects for two 700 mb wind direction categories was according to the following scheme: (1) For five snow seasons (November-April) map dates and times at which the synoptically-indicated temperature-dewpoint spread over the Park Range was ~ 50e at 700 mb and/or 500 mb, and ~ 100e at the other of these two levels, were tabulated. (2) These dates and times were divided into two categories ing to (a) synoptically-indicated 700 mb wind direction more southerly than 2400, and (b) synoptically--indicated 700 mb wind direction ~ 2400 over the Park Range.