University of Wyoming CSTAR Project: Snow Squall Case Studies

The National Weather Service (NWS) defines a snow squall as an intense short-lived burst of heavy snowfall that leads to a rapid reduction in visibility and is often accompanied by gusty winds. The combination of rapid reductions in visibility and sudden conditions from subfreezing ambient temperatures on roadways can cause high speed accidents, pileups and subsequent injuries and fatalities. The NWS in Cheyenne was part of a demonstration project in the 2017-2018 winter season that tested the value of Snow Squall Warnings. On November 1, 2018 the NWS transitioned Snow Squall Warnings from demonstration status to operational status nationwide. However, predicting snow squalls are very challenging especially in the Rocky Mountains where radar coverage is limited, models have limited predictability, and the events are very shallow. In May of 2018, the University of Wyoming (UW) in collaboration with the High Resolution Rapid Refresh (HRRR) development team and four (NWS) offices including Cheyenne implemented a CSTAR project called “Improved Operational Prediction of Blowing and Falling Snow, and Extreme Wind Events in the Rocky Mountain Region and the Northern High Plains”.

As part of this project, the NWS in Cheyenne has provided case studies to UW to reexamine snow squalls and run these cases retrospectively. The UW will also be developing a web portal that will have a Google map-based display centered on Wyoming and neighboring states (MT, ND, SD, NE and northern CO). This map will focus on snow squalls forecasts among other hazardous winter weather conditions. For the purpose of this poster, we will examine two case studies and demonstrate how the CSTAR project will aid forecasters in the prediction of snow squalls. The UW will be working with the HRRR development team to utilize the HRRR to (1) develop a derived snow squall product using HRRR output; (2) assess how well HRRR captures snow squalls, and (3) to evaluate and possibly improve the Snow Squall Parameter as a predictive tool for issuing of snow squall advisories. This information will also be validated against observations, web cams along interstates, WSR-88D Radars, and the GOES-R Daytime Cloud Phase Distinction RGB.