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<br />Tuget.control dSWE dlnerence' In" <br /> <br /> .. <br /> "" <br /> "" <br />. <br />I .. <br />, <br />. <br />" <br />t <br />I .. <br />l <br /> .00 <br /> 0 <br /> .'00 <br /> <br />, .. <br /> <br />S~'5 <br />. .Lcr"..ctrI... I <br />.Li>c rgHlr'''' <br /> <br />" I <br /> <br />., <br /> <br /> <br />" <br /> <br />" n <br />.. - <br /> <br />~. <br /> <br />Figure 4. Control area dSWE values subtracted from those of the (San Juan) larget area, expressed as <br />a percentage of the target dSWE. The dSWE values are the 24 hr integrations from SNODAS, as in Fig. <br />3. Positive (negative) percentages indicate more (less) snow precipitation in the target area relative to <br />the control area. Some bars exceed the range of y-axis the plot, so actual percentage difference values <br />are indicated near each bar. <br /> <br />signal (if any). Maps of 24 hour dSWE for each seeded day arc included in an associated <br />spreadsheet (Attachment B). Table 1 provides brief summaries of dSWE patterns in those maps. <br /> <br />The study area in southwest Coloradn was exceedingly dry through early March. The SNOTEL <br />basin average SWE through this perind was less than eight inches, but by early April it duubled <br />to nearly 17 inches (San Miguel, Animas, and San Juan River Basins). The accumulated SWE as <br />a percent of average peak SWE in these basins increased from 6% to 31% during this month. <br />long period. Therefore, while still unusually dry overall, the March storms were the heaviest of <br />the winter and were critical to improving water supplies in the region. It should be noted that <br />Mareh was also the period of the seeding extension. Seven of the ten days in March showed <br />more dSWE in the target area compared to the control areas (Fig. 3). Again, however, t<lrget vs. <br />control differences in terms of percentage (Fig. 4) arc too great to attribute to seeding. <br /> <br />IV. SUlIIlIHlry <br /> <br />il. Conclusions <br />For the primary variable of this study, we used 24 hour SNODAS dSWE, areally averaged over <br />the target and control areas, as a proxy for snow precipitatiun. The results did not indicate any <br />systematic increase or decrease in dSWE in the target vs. control areas that might be attributable <br />to WWC's cloud seeding. It appc<tred that the principal controls on spatial dilferences between <br />the target and control area dSWE were the trajectories, speeds, and internal snowfall variations <br />of the winter st()rms that produced the total dSWE across the region. If there were seeding- <br /> <br />H <br />