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<br />The differences in hourly values are shown on figure 2 where the abscissa is the Belfort <br />observations subtracted from the ETI observations. The maximum difference was 0.03 in. <br />with all other values between -0.02 and 0.02 in. The difference between the two gauges was <br />in the range -0.01 and 0.01 in. for 88 pct of all hours. This agreement is remarkable <br />considering that 0.01 in. is the resolution of the ETI gauge. Real differences of this <br />magnitude could be expected over a 10-ft horizontal distance between gauges in the small <br />clearing. <br /> <br />The accumulated hourly precipitation from the two gauges is shown on figure 3, plotted as <br />a double-mass curve. Departures from a straight line are minor. The figure shows that the <br />ETI gauge accumulated more precipitation than the Belfort, 5.16 in. vs 4.98 in., which is <br />about a 3.5-pct difference. Much of this difference is suspected to be caused by the 28 h with <br />snowfall indicated by the ETI gauge when none was observed by the higher resolution Belfort <br />(i.e., usually when no snow was falling). <br /> <br />Figure 4 is a plot of accumulated precipitation from the two gauges over the 179 h with <br />indicated snowfall. This portrayal is similar to a chart record if snowfall was continuous <br />throughout the test period. The slope of the ETI gauge "followed" that ofthe Belfort over the <br />entire test period with only minor exceptions. <br /> <br />The 10 available snowboard observations are plotted against gauge accumulations for the <br />same periods, which ranged from 1 to 10 days, on figures 5 and 6. The linear correlation <br />coefficients are 0.99 in., each case indicating the gauge totals were highly related with <br />snowfall on the snowpack surface. <br /> <br />The regression equations between the gauges and snowboard suggest that each gauge caught <br />less snowfall than actually fell on the surface. The measurements are shown in table 1, <br />which indicates the ETI and Belfort gauges respectively caught 0.31 and 0.49 in. less than <br />the snowboard over the entire period. These values represent undercatches of 6 and 9 pct, <br />presuming the snowboard accurately represented actual snowfalL <br /> <br />Table 1. - Comparison of snowboard and precipitation gauge observations. <br />Dates (1993) Board (in) ETI Gauge Belfort Board-ETI Board-Belfort <br /> (in) Gauge (in) (in) (in) <br />2/16-2/17 0.378 0.30 0.285 0.08 0.09 <br />2/17-2/19 0.358 0.38 0.360 -0.02 0.00 <br />2/19-2/20 0.938 0.88 0.870 0.06 0.07 <br />2/20-2/22 0.331 0.30 0.295 0.03 0.04 <br />2/22-2/24 0.954 0.93 0.885 0.02 0.07 <br />2/24- 2/25 0.563 0.49 0.500 0.07 0.06 <br />2/25-3/11 0.127 0.16 0.115 -0.03 0.01 <br />3/11-3/15 0.990 0.88 0.820 0.11 0.17 <br />3/15-3/18 0.240 0.22 0.270 0.02 -0.03 <br />3/18-3/28 0.595 0.62 0.580 -0.02 0.02 <br />Totals 5.474 5.16 4.980 0.31 0.49 <br /> 3 <br />