Interpreting orographic snowfall patterns

Abstract

Winter precipitation in mountainous southwest Colorado was related to terrain slope and elevation by multiple regression. From a 12 season record of 15 daily precipitation stations, the study used only those days with ≥ .01 in. at ≥ one station. Days used were classed by mean 24 hour 700mb wind direction and speed. By class, each station's mean 24 hour precipitation was computed as was station slope over 8 distances. These precipitation values were correlated to elevation and to products of terrain slope X 700mb wind speed X 700mb mean saturation mixing ratio lapse rate. (Products are simplified factors in an orographic precipitation formula.) Multiple correlation coefficient ranged between 0.80 and 0.98 for both speed and direction constant and was 0.68 for both variable. Correlation to elevation was negligible. Thus, slope explained most of the areal precipitation distribution. For each of two test years, correlation between computed and observed seasonal precipitation was ≥ 0.92. Technique refinement into a short term predictor seems feasible.