WCD-11. Developing a fire weather index for use with convection-allowing model (CAM) forecasts

Abstract
Recent fire seasons in the western US, with the associated threats to populated areas and the scale of the resources required for firefighting, have underscored the importance of accurate fire weather forecasts in the short range (next 1-2 days). Convection-allowing models (CAMs), with their capability to accurately depict the evolution of deep, moist convection as well as terrain-driven flows, can help to address this need. In this study, we describe work towards defining a fire weather index that synthesizes output from an hourly operational CAM system, the High-Resolution Rapid Refresh, in order to represent the potential for explosive fire behavior. Many fire weather indices have been developed in the past, but they have generally been developed for use with daily weather forecasts or observations. For example, the Hot-Dry-Windy (HDW) index provides one value per 24h day. There is a need for fire weather indices that evolve on shorter time scales, to provide guidance regarding evolving mesoscale fire weather threats such as thunderstorm gust fronts and other sub-daily weather phenomena. A fire weather index applied hourly to CAM output can provide guidance on changing fire weather conditions associated with these phenomena. We demonstrate the ability of the index to predict fire activity by comparing against polar-orbiting satellite-detected fire radiative power. The index is intended both to provide forecaster situational awareness for fire weather forecasting, and also to modulate fire emissions within a coupled smoke forecasting system. While there are a number of limitations inherent to this comparison (including the infrequency of satellite overpasses, obscuration of fire heat signatures by thick smoke, and uncertainty associated with fuel variability and the varying impacts of fire suppression activities), this novel fire weather index represents a starting point for further research on the prediction of dangerous fire weather conditions.