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<br /> <br />similar characteristics of other stations in the <br />area during the same time period. However, such a <br />relationship may not necessarily hold over time as <br />Figure 3 illustrates. Correlations between Durango <br />and four stations (Fort Lewis, Ignacio, Silver ton, <br />and Telluride) have been computed for overlapping <br />25 year periods (1914-1938) to (1944-1968) and <br />there is clearly a much lower correlat10n between <br />the stations at the beginning of the record compared <br />to the most recent period, that is, the correlation <br />field is much weaker for the early p~rt of the <br />record. This fact should be borne in mind in <br />interpreting the running mean and other analyses <br />presented below. No obvious relationship was <br />found between inter station corrrelations and dis- <br />tance to and/or elevation of adjacent stations. <br />Similarly no clear relationship exists between the <br />correlation fields and regional patterns of preci- <br />pitation variability. <br /> <br />Precipitation Variability <br /> <br />Of most direct interest to the cloud seeding project <br />is the variability of precipitation in the San Juan <br />area both annually and seasonally, and its variation <br />over time. Coefficients of variation of annual <br /> <br />o <br />HORSEFLY <br /> <br />30% <br /> <br />I <br /> <br />NO~WOOD /' <br /> <br />/ 20% <br />PLACE~VI/ .OURAY <br /> <br /> <br />TELLURIDE. 0 I~ONTON <br />(AMES. SAVAGE EUREKA <br />BASIN 0 0 <br />GLADSTONE <br />TROUT LAKE. / <br /> <br />25% ~TON <br /> <br />.RICO <br /> <br />\ <br /> <br />.PLEASANT VIEW <br />, <br />.YELLOW JACKET <br />.\ <br />DOLORES <br /> <br />.COftTEZ\ ":"., <br /> <br />. <br />MESA VERDE <br />NATIONAL PARK <br /> <br /> <br />IGNACIO <br />. <br /> <br />precipitation were calculated for a larger number of <br />stations for the period 1950-1968 and for a select <br />number of stations for the period 1914-1968, accord- <br />ing to the formula <br /> <br />V = (~) (100%) <br />x <br /> <br />where V is the coefficient of variation, s is the <br />sample standard deviation, and x is the sample mean. <br /> <br />For the most recent period, 1950-1968, spatial <br />variations of the annual V were mapped (Figure 7). <br />It is clear that the variability so measured in- <br />creases more or less radially from a core area <br />embracing the San Juan County Mountain massif and <br />the stations of Ouray, Ames, and Silverton. The <br />values range from 17.6 percent at Ames to 43.6 per- <br />cent at Wagon Wheel Gap. Winter variability <br />(Figure 8) showed a smaller range in values from <br />21.1 percent at Ouray to 37.3 percent~at Dolores. <br />Again variability decreased away from the San Juan <br />County massif. The generally lower winter values <br />suggest, as one might expect, that cyclonic precipi- <br />tation during these months exhibits less variation <br />than during the summer months for all stations in <br />the area. <br /> <br /> <br /> <br />LAKE <br />.CITY <br /> <br />.LOS PINOS PASS <br /> <br />/ I <br /> <br />oCATHEDRAL <br /> <br /> <br />( <br /> <br />SANTA MARIA <br />· RESERVOIR <br /> <br />N <br /> <br />T <br /> <br />1 <br />j <br /> <br />o 5 10 15 20 25 30 <br />I. ..1 I I I I <br /> <br />SAN ~ ECOLOGY PROJECT <br /> <br />. Precipitation stations operative 1968 <br />o Precipitation stations no longer in operation <br /> <br />CUMBRES <br />. <br /> <br />Scale of Miles <br /> <br />Figure 7. Annual Coefficient of Variation, 1950-1968. <br /> <br />48 <br />