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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />The average VPS was calculated for each of the nine Minnesota snow storms of <br />table 1. Most of these storms were characterized by relatively light snowfall rates, <br />compared with more moist regimes (e.g., lake effect storms, Nor'easters, mountain <br />orographic storms). In fact, accumulations in excess of 0.10 inch h-1 were rarely <br />observed by surface gages, and the large majority of hours were in the trace to light <br />snow category. The limited range of hourly SWE accumulations has hindered <br />development of stable Ze-SWE relations with the optimization scheme described by <br />Super and Holroyd (1996; 1997a). However, the relation which was used results in <br />agreement of average gage-observed and radar-estimated SWE accumulations. The <br />exponent of 2.0 has been found valid at a number of other locations and has some <br />theoretical support (Super and Holroyd 1997a). <br /> <br />Table 1. - Summary of average hourly SWE accumulations (mm h-1) for nine Minnesota snow <br />storms. The average SWE values were calculated from regression equations fit to radar-estimated <br />SWE for the 5 lowest beam tilts near 35 km range. The variance explained refers to these linear <br />regressions. Values of average SWE are given only for the lowest (380 m) and highest (2700 m) <br />sampling levels above the radar. Ratios of the greatest to least SWE values are listed. <br />Storm Start (UTC) Stop (UTC) Average Average Ratio: Percent <br />No. YYMMDDIHH YYMMDDIHH 380m 2700 m 2700/380 Variance <br /> SWE SWE <br />1 961120/15 961121/08 0.594 0.412 0.69 100 <br />2 961215/00 961215/15 1.024 0.844 0.82 96 <br />3 961217/20 961218/18 0.144 0.080 0.56 96 <br />4 961222/22 961224/07 0.406 0.217 0.53 99 <br />5 970104/20 970105/13 0.380 0.310 0.82 68 <br />6 970109/20 970110/14 0.145 0.083 0.57 93 <br />7 970122/16 970123/04 0.462 0.134 0.29 98 <br />8 970123/22 970124/05 0.409 0.202 0.49 100 <br />9 970303/21 970304/24 0.529 0.260 0.49 99 <br /> <br />Storm periods were defined by the presence of detectable hourly SWE <br />accumulations (at. least 0.005 inch) in at least 2 of the 6 available sensitive <br />weighing precipitation gages, each equipped with a wind shield. Gaps of up to <br />about 3 h with no detectable snowfall occasionally existed within the designated <br />storm periods. Five of the gages were located approximately along a line west- <br />northwest of the radar at ranges between 31 and 118 km, and one was located 41 <br />km southeast of the radar. Surface temperature and other records were examined <br />to ensure that all snowfall was dry. One storm was rejected because the calculated <br /> <br />4 <br />