Life after ASOS (Automated Surface Observing System) -- Progress in National Weather Service snow measurement

TitleLife after ASOS (Automated Surface Observing System) -- Progress in National Weather Service snow measurement
Publication TypeConference Proceedings
Year of Conference2000
AuthorsDoesken, N. J., and McKee T. B.
Conference Name68th Annual Western Snow Conference
Series TitleProceedings of the 68th Annual Western Snow Conference
Date PublishedApril 2000
PublisherWestern Snow Conference
Conference LocationPort Angeles, Washington
KeywordsAutomated observation system, Snow measurement

The National Weather service is the primary source for snow measurements for areas of our country where most people live and work. Through its networks of first-order and cooperative stations, snowfall data are available for nearly every county of our country dating back many decades.Important changes have occurred in NWS weather observations that are affecting the continuityof snowfall data. The single greatest change was the deployment of the Automated Surface Observing System (ASOS) at hundreds of airport weather stations across the country during the 1990s. ASOS does not measure snowfall or snow depth. It utilizes a heated tipping bucket rain gauge for measuring both rain and the water content of snow. This type of gauge tends to under measure the water content of precipitation that falls as snow, especially at temperatures well below the freezing point.New snow measurement guidelines were implemented in 1996 to expand the use and consistency of snow data from cooperative observers. These guidelines allow snowfall measurements at intervals of no less than once daily to no more than once every six hours. Data were collected for two winters at volunteer locations in several states to assess the impact of measurement interval on measured snowfall. Results show that the time interval between measurements does affect the reported snowfall totals. Measurements taken every six hours produced snowfall totals 19% greater than measurements taken once each day. Similarly, measurements taken every hour produced snowfall totals 15' greater than if measured only once at the end of each 6-hour period. This suggests that data users must beware of this characteristic before analyzing time series or spatial snowfall patterns from different types of weather stations.