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ARS Home » Pacific West Area » Boise, Idaho » Northwest Watershed Research Center » Research » Publications at this Location » Publication #101823
Title: VERIFICATION OF NEXRAD SNOW AND RAIN ACCUMULATION ESTIMATES AT THE REYNOLDSCREEK EXPERIMENTAL WATERSHED

Author
item Levinson, David
item HANSON, CLAYTON

Submitted to: American Meteorological Society
Publication Type: Proceedings
Publication Acceptance Date: 7/12/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: The estimation of rainfall accumulation using radars is a difficult task in most atmospheric conditions and locations. However, measuring snowfall is even more difficult because of the complexity of snow crystals and other solid precipitation particles. This paper addresses the verification of Next Generation Weather Radar (NEXRAD) WSR- 88D Level III snow and rain accumulation estimates using dual-gauge measurements from an instrumented watershed in the Owyhee Mountains of southwest Idaho. The verification was conducted using the dual-gauge technique (Hamon 1973) where an unshielded and shielded pair of co-located gauges are used to determine the "actual" catch at the surface. The verification data used for this study is from the Reynolds Creek Experimental Watershed (RCEW) in the Owyhee Mountains. All precipitation amounts were accumulated to hourly totals for comparison with NEXRAD measurements. The NEXRAD standard algorithm underestimated snow at all RCEW sites. The radar uncertainty of any individual hourly estimate was small, but this effect translated to a significant under-catch when the precipitation lasted more than one day.

Technical Abstract: The estimation of rainfall accumulation using radars is a difficult task in most atmospheric conditions and locations. However, measuring snowfall is even more difficult because of the complexity of snow crystals and other solid phase hydro-meteors. This paper addresses the verification of Next Generation Weather Radar (NEXRAD) WSR-88D Level III snow and rain accumulation estimates using dual-gauge measurements from an instrumented watershed in the Owyhee Mountains of southwest Idaho. The verification was conducted using the dual-gauge technique (Hamon 1973) where an unshielded and shielded pair of co-located gauges are used to determine the "actual" catch at the surface. The dual-gauge measurements are a better comparison with NEXRAD, or other remotely derived accumulation measurements, since it is an estimate of the "actual catch" instead of an uncorrected shielded or unshielded gauge measurement. The verification data used for this study is from the Reynolds Creek Experimental Watershed (RCEW) in the Owyhee Mountains. All gauge precipitation amounts were accumulated to hourly totals for comparison with NEXRAD measurements. The NEXRAD standard Z-R algorithm underestimated snow at all RCEW sites. It was found that the bias of any individual hourly estimate was small, but this effect translated to a significant under-catch when the precipitation lasted more than one day.