Warn on Forecast: WoFS

Warn-on-Forecast is a National Oceanic and Atmospheric Administration (NOAA) research program tasked to increase tornado, severe thunderstorm, and flash flood warning lead times.

The NOAA Warn-on-Forecast (WoF) research project has developed a convection-allowing ensemble analysis and forecast system designed to provide short-range (0–6 hr) guidance for thunderstorm hazards. This system— the NSSL Experimental Warn-on-Forecast System (WoFS)—has been run in realtime for Hazardous Weather Testbed experiments since 2016, including the NSSL Spring Forecasting Experiment and Flash Flood and Intense Rainfall Experiment. The WoFS forecasts provide rapidly-updating, probabilistic forecasts of the likelihood and severity of threats such as tornadoes, severe hail, damaging winds, and flash flooding within thunderstorms.

The current configuration of the WoFS consists of an ensemble of 36 individual members that are initialized within the Earth System Research Laboratory’s High-Resolution Rapid Refresh Ensemble (HRRRE). The WoFS domain is centered over expected areas of severe weather during the day and covers a 900 x 900 km region with 3-km grid spacing. Conventional and remotely sensed observations, including radar reflectivity, radial velocity, and GOES-16 cloud water path, are assimilated into the WoFS every 15 minutes using the GSI-Ensemble Kalman Filter (EnKF) package. The WoFS forecasts are issued with 18 members every half-hour, depending on the phenomenon of interest, and are up to 6 hours in length with output available every 5 minutes.