Impacts of Snow Squalls on Pennsylvania Roadways

To learn more about the impacts of snow squalls on vehicle crashes in Pennsylvania, a study of Pennsylvania Department of Transportation (PennDOT) crash data and weather data between the months of October and March was conducted for a nine year period (2007-2016). A total of 111 “snow squall events” were identified, averaging 12-13 snow squall events per year. Archive radar data and surface observation plots from the Weather Prediction Center were used to identify snow squall events, whose maximum reflectivity reached or exceeded 30 dBZ. Snow squall events ended when convective snow bands dissipated or exited Pennsylvania.

To generate useful outreach statistics for the national rollout of the Snow Squall Warning (SQW) product, this study defined a snow squall day as any day (midnight-midnight local time) during which a snow squall event occurred (i.e., any day at least partially falling within a snow squall event window). Using this specific dataset, generalized statistics were calculated through an analysis of the degree to which crash numbers increased on snow squall days.

Preliminary results suggest that on an average snow squall day, the state of Pennsylvania sees about 17% more car accidents than on days without snow. Even more noteworthy is that on the average snow squall day, 60% more vehicle pileups (6+ unit crash clusters) occur on Pennsylvania roadways than on days without snow. These statistics, along with case studies detailing specific snow squall-related accidents, will be used to bolster safety messages and calls to action in social media posts and partner weather briefings to more fully advise core NWS partners and the public of the dangers of snow squalls.