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lable 3. - Comparison of radar-estimated hourly snowfall accumulations and standard errors of estimates for array a~erages and the nearest neighbor range bin. A verage Radar-Estimated Snow (inch) Nearest Site Gage Array Neighbor CLE 1 0.0196 0.0197 CLE 2 0.0173 0.0173 CLE 3 0.0160 0.0160 DEN 1 0.0185 0.0196 DEN 2 0.0221 * 0.0206 DEN 3 0.0207** 0.0176 Standard Error of Estimate (inch) Nearest Array Neighbor 0.0136 0.0137 0.0140 0.0139 0.0224 0.0228 0.0125 0.0131 0.0171 0.0169 0.0119 0.0122 * 1 obviously contaminated bin ignored ** 4 apparently contaminated bins included - see text snowflakes over the region viewed by a radar during any given volume scan. However, the actual fall speeds are not measured by the radar or by any other means. Therefore, to calculate possible advection of snowflakes, a single constant fall speed must be assumed to estimate a particular trajectory. A range of likely fall speeds was used to determine if any of the tested values were superior in the advection I scheme. I ~tarting with the ground elevation at each range bin position, the horizontal advection for each given assumed fall speed was calculated upward in 305-m steps until a position was reached within 1 m of the cbnter of the lowest available (O.5-degree tilt) radar beam. The reflectivity value in the range bin i~tersected by the reverse trajectory calculation was saved for later SAA calculations and comparison with glround gage and snow board observations. I 1fe recommended Ze-S relation for Cleveland (section 5.1) was used to estimate the hourly SWE from ~e four range bins, corresponding to the four assumed fall speeds, upwind from each of the five Universal gages. R values were then calculated between these radar-estimated SWE values and the gage- rlteasured hourly SWE accumulations as given in table 4. Similar calculations were made for the three I Denver gages and the Denver NWS WFO snow board observations, all located within 49 km of that r~dar, also shown in table 4. Too few observations were available for calculations with the other Denver I . gages at farther ranges. I li'he Cleveland R values of table 4 are greatest for 0.0 m S.l, that is, for no advection but simply using the ~earest neighbor range bin directly over each gage. Gage 3 R values are identical for 0.0 and 2.0 m S.l. Other obvious characteristics of Cleveland data are the tendencies for R values to decrease with slower ffl speeds and with greater ranges from the radar. These results are interpreted as largely caused by the increasing advection distance with slower fall speeds and greater height above the ground at increasing I range. 10