Developing Dry Thunderstorm Verification Tools to Improve Fire Weather Forecasting at NOAA’s Storm Prediction Center

Dry-thunderstorm initiated wildfires represent 54% of the total land area burned by wildfires in the contiguous U.S. from 1992-2020, yet uncertainties in assessing fuel moisture remain a major challenge in predicting the occurrence of dry thunderstorms. The National Weather Service (NWS)’s Storm Prediction Center (SPC) issues daily Dry Thunderstorm Outlook areas in its fire weather outlooks corresponding to areas with dry fuels, rainfall accumulation less than 0.10”, and at least 10% (Isolated) or 40% (Scattered) coverage of cloud-to-ground lightning within 20 km of a point. Here, differences in percentiles of Energy Release Component (ERC), a measure of fuel availability to burn, are first compared across two sources–WFAS (Wildland Fire Assessment System) and gridMET (the Gridded Surface Meteorological dataset). A new calculation of the gridMET ERC percentiles is performed based on aggregated data over all days in the 44-year record (1979-2022). Case studies confirm that the relevance of each of the three sets of ERC percentiles changes with seasonality. A daily verification plot then combines cloud-to-ground lightning flashes from the Vaisala National Lightning Detection Network, fuel readiness from the WFAS and gridMET sources, and daily Fire and Thunderstorm Outlooks issued by SPC. Additionally, flash counts within SPC isolated/scattered Dry Thunderstorm Outlook areas and Stage IV precipitation data from the National Centers for Environmental Prediction at each flash location are analyzed to evaluate existing precipitation thresholds for dry thunderstorms. These tools will provide essential next-day fire weather forecasting feedback for forecasters at the SPC and potentially NWS Weather Forecasting Offices across the country.