New Verification Techniques for FACETs: Geospatial Warning Verification System Performance on the 2007-2015 Storm-based Tornado Warning Database

NWS severe thunderstorm and tornado warnings are issued today as deterministic polygons that cover a two-dimensional area of expected threat of severe weather within a time period usually from 30 to 60 minutes.  As part of the Forecasting A Continuum of Environmental Threats (FACETs) initiative, new methods of delivering severe thunderstorm and tornado forecast and warning information are being investigated.  One of the stated goals of FACETs is to produce a reduction in warning false alarm areas (FAA) by 30%, even for warnings that verify as a “hit” by today’s standards.  However, FAA is not a current warning verification measure employed by the National Weather Service.  A new gridded warning verification technique (shown at previous NWA Annual Meetings) includes FAA, along with other innovative measures such as false-alarm time and location-specific lead and departure time.

A real-time verification system that uses the above techniques is planning to be deployed as part of the Probabilistic Hazard Information (PHI) tool under development for AWIPS2.  One of the first steps in the development of this system is to stress test it with a very large data set.  The system was optimized to increase processing speed by 40x.  The entire storm-based tornado warning data set from October 2007 to December 2015 was processed.  Annual, monthly, and hourly statistics have been calculated, showing the variation in warning performance across those time spaces.  Geospatial coverage maps of lead time, departure time, and false alarm time have also been created.