A Mesoscale Simulation of a Mountain Wave Wind Event Associated with the Chimney Tops 2 Fire (2016)

Mountain wave wind events occurring on the northwest-facing side of the southern Appalachians have been identified as a source of strong low-level winds and adiabatic warming under certain synoptic patterns. Previous research relying on observations and mesoscale models has found that predicting the timing and magnitude of mountain wave events in the region represents a particular forecast challenge.

In this study, a 4-km Weather Research and Forecasting (WRF) mesoscale simulation is shown to reproduce observed characteristics of mountain waves that developed as rapid fire spread occurred during the Chimney Tops 2 fire (November 2016). Observations and model simulations from the event indicate that southerly low-level winds greater than 30 m s^-1 occurred over the burn area. Comparing the 4-km simulation and local soundings with a mountain wave climatology for the region indicates that this case exhibited an anomalously dry layer between 1.5 and 3.5 km above sea level upwind of the fire location. We hypothesize that this steep vertical moisture gradient produced changes in atmospheric density, which then contributed to an amplification of the vertical motion associated with the mountain waves. Amplification of the mountain waves could have exacerbated the hot, dry, and windy meteorological conditions that contributed to the observed fire behavior during the fire.