All-Weather Precipitation Accumulation Gauge Comparisons with Standard NWS 8-inch Manual Gauge

The National Weather Service (NWS) Automated Surface Observing System (ASOS) field sites use the Frise heated tipping bucket gauge for reporting precipitation accumulation. The gauge can measure liquid accumulation but is not designed to accurately measure freezing or frozen precipitation. Therefore, the ASOS Program has directed concept exploration phase testing of All Weather Precipitation Accumulation Gauges (AWPAG) at Sterling, Virginia and Johnstown, Pennsylvania. The comparison results of the 1998-1999 winter test season show the automated and unattended candidate AWPAG gauges provide improvement over the current operational Frise heated tipping bucket gauge when compared to the NWS standard 8-inch non-recording gauge in winter precipitation events.

Two vendors were selected to participate in this winter test season (1 Dec. 1998 - 19 April 1999) and each provided four candidate AWPAG sensors. Two gauges from each vendor were installed at Sterling and two from each vendor were installed at Johnstown. Both of the vendors' gauges are 40 inch capacity automated weighing type gauges. Each gauge has a controlled orifice heater. All gauges were installed with wind shields to reduce wind turbulence. Hourly and event comparisons to the reference 8-inch gauges were made in liquid, freezing, frozen, and mixed precipitation. False accumulation reports in the absence of precipitation were tracked and are also reported.