High-Resolution Rapid Refresh model-based analysis of snow squall characteristics

National Weather Service (NWS) forecasters have recently been encouraged to issue new warnings for a hazardous weather type, snow squalls. Snow squalls are intense, but limited duration, periods of moderate to heavy snowfall typically accompanied by high surface winds, resulting in reduced visibilities and whiteout conditions. Because this type of alert is new, the frequency and intensity of snow squalls must be studied, and the ability of operational high-resolution models to accurately capture snow squalls needs to be assessed. In many regions, model guidance will be more important than observations in issuing snow squall warnings given the relatively poor coverage of the Weather Surveillance Radar, 1988, Doppler (WSR-88D) radar network because of terrain blockage and relatively sparse radar locations.

Given the relatively small scale of snow squall events, i.e., not captured by global and even some regional numerical weather prediction (NWP) models, we analyze three cool seasons (Nov-Apr, 2016-2017, 2017-2018, and 2018-2019) of High-Resolution Rapid Refresh (HRRR) model output to determine the characteristics of snow squalls and their component hazards including low visibility, high wind gusts, snowfall, and abrupt surface freezing. Furthermore, we analyze the occurrences of co-located modelled hazard components, measure against known snow squall cases, and investigate the HRRR’s capability to predict snow squalls via the Snow Squall Parameter (SNSQ) in the High Plains and Mountain West. Future work includes the dissemination of real-time HRRR-driven snow squall forecasts and an investigation into the viability of higher-resolution HRRR-like WRF model forecasts.

Bob Capella, Ethan Collins, Zachary Lebo, Bart Geerts
University of Wyoming

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