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<br />35 <br /> <br />i <br /> <br />The values of D in Fig. 9 range from a minimum of 0.72 in the San Luis <br />Valley to 0.86 near the Continental Divide, A large value of D is <br />related to a stable climate region with only small year to year <br />variations from the median. For example, a value of 0.86 indicates that <br />the location has only a 14% reduction of precipitation from the median <br />for a rather dry year. At the other extreme a low val ue of 0.72 <br />indicates that a reduction of at least 28% in precipitation occurs in a <br />dry year. The pattern in Fig. 9 indicates that the precipitation has a <br />smaller variation in the mountains and a larger variation in the San <br />Luis Valley, northern Front Range, and east central plains. Most of the <br />Western Slope is of a moderate variability and a few locations in the <br />Eastern Plains have smaller variability. Figure 9 can be read to an <br />estimated accuracy of + 0.02 for determination of the 0.20 probability <br />precipitation value for a given location. <br />31 Precipitation in wet years, Using a similar definition, a wet <br />year in Colorado is defined as a year when the total precipitation is in <br />the wettest 20% of all yearly totals. The threshold value separating a <br />wet year from all other years is therefore a precipitation amount with <br />exactly a 0.80 nonexceedance probability. The ratio of the 0.80 <br />probability precipitation value to the median (0.50 probability) value <br />indicates the relative difference between a wet year and the median <br />year. The ratio of the 0.80 probability precipitation to the 0.50 <br />probability precipitation is designated as factor on and is given in <br />Fig. 10. This factor may be used with other factors to determine the <br />0.80 probability precipitation, p(0.801 as follows: <br />P(0.801 = W x M x PA . <br /> <br />. <br />