Cool Season Small Hail over the West Coast of the United States: Environments, Hazards, and Decision Support

The environments and hazards associated with small hail accumulating across west coast roadways have been examined. Showers forming within a cold deep-layer airmass collocated with a weakly unstable environment characterize the atmosphere of most events. Furthermore, small hail showers are generally low-topped with max reflectivity values averaging 48 dBZ. Despite the generally unremarkable radar presentation, swaths of accumulating hail are observed with many showers moving east across the coast of northwest California during the cool season.

Forecasters at the National Weather Service (NWS) in Eureka, CA have evaluated past events and concluded that hazardous driving conditions are amplified when small hail accumulates across low elevation travel corridors, possibly because the public perceives that icy roads don’t occur at elevations near sea level. For instance, the public generally understands that heavy snow is common across the mountains, while heavy rain prevails at low elevations. Motorists are caught off-guard when wet, relatively warm, low elevation roadways suddenly transition to icy hail covered conditions. This presentation will highlight the environmental conditions that signal the potential for impactful small hail accumulations. The environmental analysis will be supplemented with a summary of enhanced IDSS techniques used to alert the public and partners within the NWS Eureka county warning area.