Objective identification of thunderstorm gust fronts in numerical weather prediction models for fire weather forecasting
James F. Bresch
A C , Jordan G. Powers A , Craig S. Schwartz A , Ryan A. Sobash A and Janice L. Coen A B
A National Center for Atmospheric Research, Mesoscale and Microscale Meteorology Laboratory, PO Box 3000, Boulder, CO 80307, USA.
B University of San Francisco, 2130 Fulton St., San Francisco, CA 94117, USA.
C Corresponding author. E-mail: bresch@ucar.edu
International Journal of Wildland Fire 30(7) 513-535 https://doi.org/10.1071/WF20059
Submitted: 22 April 2020 Accepted: 8 April 2021 Published: 19 May 2021
Abstract
Abrupt changes in wind direction and speed can dramatically impact wildfire development and spread, endangering firefighters. A frequent cause of such wind shifts is outflow from thunderstorms and organised convective systems; thus, their identification and prediction present critical challenges for fire weather forecasters. Here, we develop a methodology and implement it in a software tool that can identify and depict convective outflow boundaries in high-resolution numerical weather prediction (NWP) models to provide guidance for fire weather forecasting. The tool can process model output, objectively identify gust fronts, and graphically display detected gust fronts and similar boundaries in NWP model forecasts. The tool is demonstrated with output from the Weather Research and Forecasting (WRF) model from the operational High-Resolution Rapid Refresh (HRRR) forecasting system and from a WRF ensemble run at the National Center for Atmospheric Research that can provide probabilistic information about model-predicted gust fronts. The tool can identify outflow boundaries in model forecasts of convective events occurring in both simple and complex terrain, both with and without concurrent wildfire activity. With accurate underlying model forecast output, the tool can reliably reveal areas of potential gust front activity and thus provide valuable guidance to incident meteorologists and command personnel.
Keywords: WRF, outflow boundary, gust front, HRRR, mesoscale model, ensemble forecasting, multiple directional non-maximum suppression, Yarnell Hill.
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