An evaluation of a turbulent kinetic energy based fire-weather index during large wildfire events in the western United States

Turbulence in the atmospheric boundary layer can affect fire dynamics and smoke dispersion, and yet most fire-weather and fire-behavior indices do not account for boundary-layer turbulence. Several case studies have linked large fires in the western Great Lakes region and the northeastern U.S. to episodes of significant turbulence in the ambient atmosphere. More specifically, the case studies indicated that periods of rapid fire growth in these regions frequently happen when values of the product of the Haines Index (HI) and turbulent kinetic energy (TKE) exceed a threshold indicative of highly turbulent conditions in a dry and unstable boundary layer. The behavior of this new index (HITKE) during large wildfires in other regions of the U.S. has yet to be examined. In this study, we assess the spatial and temporal patterns of the HI and HITKE during and in the vicinity of major wildfire events that have occurred in the western U.S. using North American Regional Reanalysis (NARR) data and output data from the Weather Research and Forecasting (WRF) model. The HI and HITKE results are compared to determine whether the HITKE index may be a better discriminating atmospheric indicator of the potential for extreme or erratic fires in the western U.S. than the HI alone.