An Hourly Wildfire Potential Index for Predicting Subdaily Fire Activity Based on Rapidly Updating Convection-Allowing Model Forecasts
Journal Article
Overview
abstract
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 24-h period. Extreme wildfire activity in the western United States 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 a proof of concept for an hourly fire weather index developed specifically for application within a rapidly updating convection-allowing model. The index, termed the hourly wildfire potential (HWP), is developed based on observations of fire radiative power (FRP) from polar-orbiting satellites during large western U.S. wildfires in 2018 and 2020 and is evaluated against a merged dataset of FRP from polar-orbiting and geostationary satellites. The index is computed based on meteorological output from the NOAA operational High-Resolution Rapid Refresh (HRRR) model. The HWP index exhibits an improved representation of hourly FRP compared to a climatological approach and also shows promise for distinguishing between conditions associated with flaming and smoldering combustion. This work paves the way for improved prediction of wildfire smoke emissions in the coming hours and days.; ; Significance Statement; A new hourly wildfire potential index, intended to capture the effects of hour-to-hour weather variability upon ongoing wildfire activity, is developed and applied to forecast output from a state-of-the-art convection-allowing numerical weather prediction model. Forecasts of the index for a number of large western U.S. wildfires from recent years, based on once-per-day model simulations, demonstrate that the index is able to skillfully predict increases in wildfire activity due to changes toward hotter, drier, and/or windier conditions, as well as reductions in fire activity due to increased humidity and precipitation. We anticipate that this index can help forecasters anticipate sudden changes in wildfire activity, as well as predict wildfire smoke emissions, leading to improved decision support for fire management and enhanced communication with communities impacted by fire and smoke.;
