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I', .I. I I I I I I I I I I I I I I I I ~ 1 I I 1 ~I~ ., An examination to determine. the degree to which wind -slope alignment effects could be delineated was made. The study covered the periods November-March for ten seasons (1955-1965). Twenty ESSA clima- tological daily precipitation stations in or. near the project area were used. (Only sunset-reading stations were used.) Twenty-four hour precipitation. totals were tabulated for each station. and a precipitation- day was defined as one in which measurable precipitation occurred at at least one of the twenty stations. Thus. most of the completely dry days were eliminated. especially since Wolf Creek Pass IE was one of the stations used. Vector.24-hour mean 700mb wind directions at Grand Jct; were ta.bulated for each of the 'days in the resulting set of precipitation days. Twelve 300 direction categories were designated running consecutively c1ock- /~ wise. The limits of category 1 were 1750 to 2040. category 2 2050 to 2340. etc. The precipitation day data set was then stratified by direction category. Each station's 24-hour ~erage (5ii) was computed for each category i. (Table 1) The ratio"';- (where x is the station average over all direction categories) was computed for each station. This ratio is a dimensionless variable and is co.ntourable when plotted on an area map. Ratio values were plotted (on maps showing. the main topographic features) for each direction category and the ratio field contoured. Contouring was done according to station. ratio values and also purposely considered r:qajor barrier orientations. (That is. barrier orientation and location effects as exemplified by ratio values at existing stations were extrapolated or interpolated into silent areas using topographic simila.rity as a guideline.) , The resulting 11 maps (since there were no occurrences in direction category 11) are listed consecutively in Appendix A ~d those for. categories 2. 5 and 8 are repeated as Figures 1. 2 'and 3. Inspection of this map set reveals two scales of topographic effects on precipitation. First of all. the upslope and downslope effects of the overall San Juan Mountain Massif are plainly evident. Also. more localized effects can be seen at most stations when. attention I is focused on a particular station for various direction categories. These localized effects (again occurring partially due to variations in wind direction relative to' the area distribution of terrain slope vectors) were studied more closely for three selected stations by superimposing on a local topographic map.a po~ar coordinate plot of x/x (i.e.. . p=x/y.: and 6= 3