An Examination of SPC Convective Watch Hazard Probability Forecasts
Jared Guyer, NOAA/NWS Storm Prediction Center, Norman, OK
Andrew Dean, NOAA/NWS Storm Prediction Center
John Hart, NOAA/NWS Storm Prediction Center
Patrick Marsh, NOAA/NWS Storm Prediction Center

The NOAA/NWS Storm Prediction Center (SPC) has been issuing probabilistic forecasts related to severe convective weather since 1999.  Convective watch hazard probabilities officially became part of Severe Thunderstorm Watch and Tornado Watch issuances beginning in 2006.  These subjective watch hazard probabilities provide value-added differentiations of the anticipated coverage and significance of large hail, damaging thunderstorm winds, and tornado hazards within a given watch area and valid time.  Furthermore, the watch hazard probabilities drive the coverage (e.g., isolated, scattered, widespread) and intensity terminology used in the SPC Public Watch Notification Message (SEL) product.  In practical terms, the watch probabilities can provide users the ability to discriminate between marginal convective watch situations versus higher-impact watches that are issued for severe-weather outbreaks (such as “Particularly Dangerous Situation” watches).  The motivation of this study is to provide results from an aggregate examination of 10 years of SPC Watch hazard probabilities in relation to observed storm reports and as a function of storm environment information.