The structure and evolution of terrain-induced meteorological features influencing the Alberta and Mack Lake wildfire environments

Determining the influence of meteorological conditions on the production of a high fire-risk environment has traditionally relied on the identification of precursor large scale weather patterns that have been empirically linked to historical wildfire events. As such, the physical processes that characterize these large-scale patterns have not been addressed. With the advent of fine-scale numerical models, historically significant cases can be examined from a synoptic-dynamic perspective in order to elucidate the nature of these processes. The current study employs output from a 120-h simulation of the first five days of May 1980, using NCAR's Weather Research and Forecast (WRF) model, to investigate the structure, evolution and role of orographically induced lower tropospheric features and processes that influenced the wildfire environments of both the Alberta Fire and the Mack Lake Fire. Chief among these features is a lee-side trough which provides the wildfire environment with low relative humidity and high momentum air through terrain induced subsidence. It is shown that such features are readily identifiable in the gridded model output and that they remain coherent structures for the several days spanning these two events. The nature of their influence on the respective wildfire environments is presented.