Factors affecting NEXRAD-based point rainfall estimation in the Seattle area

Point rainfall rate estimation by radar has many useful purposes, particularly within an urban environment. For example, such monitoring could help define driving conditions related to highway wetness and visibility impairment and predict and assess storm water runoff over spatial scales down to grid sizes of around 1×1 km². Recent implementation in the U.S. of a national radar system (NEXRAD) with comparable spatial coverage and temporal sampling at approximately five-minute intervals offers great potential for such applications. Thus, an effort to improve point rainfall estimation, using reflectivity factor measurements from the Seattle area NEXRAD WSR-88D radar, is worthwhile investigating. Major factors affecting point rainfall interpretation of radar reflectivity factor include data quantization, rainfall type, spatial filtering, storm motion, melting layer effects and time correspondence of radar and gage measurements. These and other factors are under consideration for development of a robust algorithm to retrieve reliable estimates of point rainfall rates from NEXRAD radar measurements. A sample comparison between radar-derived rainfall rate estimates and gage measurements at a distance of around 60 km from the radar illustrates the methodology in a case where melting layer interference is absent