The Frise heated tipping bucket is the operational precipitation accumulation gauge used with the Automated Surface Observing System (ASOS). The sensor measures liquid accumulation, but is not specifically designed to accurately measure freezing or frozen precipitation. The accurate measurement of liquid equivalent accumulations in all types of liquid, solid, and mixed precipitation is an important part of weather observations. The National Weather Service ASOS Product Improvement team has conducted testing of all-weather precipitation accumulation gauges (AWPAG) since 1996.

A contract for design and development of ten pre-production gauges was awarded in September 2001, to C.C Lynch and Associates of Pass Christian, Mississippi, in partnership with Ott Hydrometry of Kempton, Germany. Testing of four prototype gauges in 2002, which included the most significant proposed performance modifications, demonstrated improvements in gauge catch, accuracy, increased capacity, and communications. Qualification testing of gauges was conducted during the winter of 2002 - 2003, at the Sterling, Virginia and Johnstown, Pennsylvania test sites. This paper presents the results of the qualification testing.

In addition, AWPAGs underwent Operational Acceptance Testing (OAT) at 13 selected ASOS sites in 2003, against collocated Frise heated tipping bucket gauges in liquid precipitation. This paper also presents the data analyses and conclusions from the OAT testing.