WCD-03. An hourly wildfire potential index for predicting sub-daily fire activitybased on rapidly-updating convection-allowing model forecasts

Abstract
Many fire weather index products have been developed to assist land managers, weather forecasters, and firefighters with anticipating weather conditions that may impact existing or potential new wildland fires in coming days. Most of these indices are designed to provide a single value for an entire 24h period. Extreme fire activity in the western US in recent years, including the impact of mesoscale and microscale phenomena such as thunderstorm gust frontal passages, radiative shading by dense smoke plumes, and pyrocumulonimbus development and collapse, as well as the advent of operational convection-allowing model forecasts, has highlighted the need for a more frequently updated index. In this study, we present an hourly wildfire potential (HWP) index developed specifically for application within a rapidly-updating convection-allowing model. The index value, derived from meteorological forecasts and vegetation cover information, is compared with sub-daily fire radiative power observations from polar-orbiting satellites for a number of large wildfire cases from 2018-2020. The HWP index is able to capture a portion of the weather-related variability in fire behavior, in particular the changes in activity related to synoptic and mesoscale wind events, as well as rainfall and snowfall. Comparison with existing fire weather indices illustrates the ability of the HWP index to highlight fire weather conditions and rapidly-changing fire weather. Real-time HWP index forecasts are now being produced for CONUS and Alaska based on the operational High-Resolution Rapid Refresh (HRRR), and for North America based on the experimental Rapid Refresh Forecast System (RRFS). This development also paves the way for improved prediction of wildfire smoke emissions in the coming hours and days.