A New Snow-level Forecast Verification Tool Employing Vertically Pointing Radars and a Rapidly Updated Numerical Weather Prediction Model

The snow level, or altitude in the atmosphere where snow changes into rain, is an important variable in mountain hydrology because it determines the areal extent of a watershed that gets exposed to rain versus snow. Low snow levels contribute to snow pack, which stores water for later use. High snow levels produce rain over a greater portion of the watershed, which can lead to increased runoff and the potential for flooding depending on prior conditions in the watershed (antecedent snow pack, soil moisture, downstream reservoir storage capacity, among other factors). This paper describes a snow-level forecast verification tool that compares observed snow levels with snow levels predicted by the High Resolution Rapid Refresh (HRRR) model run by the Environmental Modeling Center at NOAA’s Centers for Environmental Prediction. The observations used for verification are from various vertically pointing radars deployed by the NOAA Earth System Research Laboratory’s Physical Sciences Division. These radars currently are deployed in California, Colorado, New Hampshire, Oregon, and Washington. For each observing site, the tool compares observed snow levels to prior forecasts from the HRRR, provides current forecasts for the HRRR, and illustrates HRRR snow-level forecast performance over the past year. A more detailed description of the tool and types of radars used in the tool will be given and case studies will be shown.