The Warning Polygon Verification Project: An alternative verification scheme for severe storm warnings

An alternative method for verifying National Weather Service tornado and severe thunderstorm warnings is discussed. The current system used to verify severe weather warnings bases its statistics on geopolitical boundaries (counties/parishes/independent cities). Since thunderstorms and tornadoes do not observe these boundaries, this verification scheme can sometimes lead to an unrepresentative depiction of forecaster skill. The proposed system uses the warning polygon generated by NWS forecasters using WarnGen, a computer-based warning generation program, as its basic unit of area. An experiment is being conducted this spring at several NWS offices to determine the utility of this verification system and its possible future applications. In spite of inherent problems with severe storm verification in general, the warning box verification system is expected to give a more realistic view of forecaster skill in detecting and tracking severe thunderstorms and tornadoes.