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<br />003409 <br /> <br />available through the courtesy of Dr. Owen Rhea, Professor Lewis Grant, and <br />the Colorado State university Atmospheric Science Department. <br /> <br />The accuracy of interpolated soundings was assessed by Rhea et al. <br />(1979), who compared values interpolated from the six National Weather <br />Service sites to actual values obtained from soundings in Craig and Durango <br />during the winter of 1977-78. They concluded that mean errors in <br />temperature, wind speed and relative humidity were relatively small, but <br />large errors occurred occasionally. Occasional large errors could affect <br />the conclusions of this study, particularly if they are systematic (more <br />likely to occur if winds are from a certain direction, for example) rather <br />than random. <br /> <br />Snowcourse water content data recorded by the Snow survey unit, Soil <br />Conservation Service, U.S. Department of Agriculture, were used to identify <br />dry, normal and wet winters and to validate our study approach.* <br /> <br />Selection and Grouping of Basins by Sub-region <br /> <br />Some of the variation in snowfall within and across basins is caused <br />by shadowing by upwind mountina barriers (moisture is removed each time air <br />passes over a barrier), and some by differences in wind direction. <br />Variability in snowfall necessitates that this analysis be conducted basin <br />by basin. Twelve basins in the mountainous area of Colorado were selected, <br />because computer-determined information on their snowfall patterns <br />(diSCUSSed later) was available and we felt they are representative of the <br />snow catchment areas in the state. The selected basins are listed in Table <br />1 and outlined in Figure 2. <br /> <br />* Snowcourses are relatively flat sites in the mountains where monthly <br />measurements of snow depth and water content are taken each winter. There <br />are presently approximately 200 sites in Colorado. Records at some sites <br />extend back to 1936. <br /> <br />10 <br />