The National Weather Service has placed the Automated Surface Observing System (ASOS) in service during the past few years with the improved Heated Tipping Bucket (HTB) rain gage starting installation in May 1996. A set of thirteen locations have been used for a comparison of ASOS rain observations with the Universal Rain Gage (UNIV).
Comparisons of observations are in two categories. Four of the 13 locations have had a standard rain gage colocated with the ASOS to evaluate performance of the ASOS HTB. All 13 locations have supplied 1 minute, hourly, and daily ASOS observations which are compared with the UNIV observations up to one mile away from the ASOS. The 13 locations are used to evaluate the data continuity. Data has now been analyzed for the period June 1996 - April 1998. Three of the four colocated comparisons show ASOS within ± 4% of a standard gage. Six to twelve hourly comparisons for 13 locations show that the average of the 13 ASOS observations are within 1% of the UNIV observation; however, there are distinct differences among the 13 locations. Two of the locations have an ASOS that provides observations enough lower than the UNIV that they edit the rain amounts. A discussion will be provided showing details of the comparisons, likely reasons for variations in the compared observations, the importance of the observations for climate applications, and the importance of metadata for climate observations in the 1990s and beyond.