The sensitivity and spatial resolution of the WSR-88D radar offers the promise of accurate estimates of precipitation in realtime. Since the radar provides more spatial detail and frequent measurements, it should improve the mapping of precipitation accumulation over what can be obtained from rain gauge data. The primary objective of this study was to compare precipitation measurements from rain gauges with accumulated precipitation estimated by the Precipitation Processing System (PPS) of the WSR-88D radar at Lockport, IL in cool season stratiform rainstorms. Another objective was to determine the conditions under which the radar and gauge measurements matched and those under which they diverged. To accomplish this, a third objective was to analyze the spatial patterns of storm-total precipitation amounts and of reflectivity on the radar images.
Data from 7 stratiform rain events were used in the analysis. The gauge/radar (G/R) ratios were tabulated in four range bands with cutoffs at ranges of 20, 40, and 50 km. Within 50 km, 90 percent of the points had G/R values > 1 (and 43 percent had G/R values > 2), indicating underestimation by the radar. Beyond 50 km the G/R values were evenly distributed about a value of 1.0.