The 2013 Rim Fire: Implications for Predicting Extreme Fire Spread, Pyroconvection, and Smoke Emissions

The Rim Fire, which burned over 104,000 ha in late 2013, was one of the most severe fire events in California's history, in terms of its rapid growth, intensity, overall size, and persistent smoke plume. The Rim Fire also endangered portions of Yosemite National Park, including the power and water supply to the San Francisco Bay Area. At least two large pyrocumulonimbus (pyroCb) events were observed, allowing smoke particles to extend through the upper troposphere over a large portion of the Pacific Northwest. However, the most extreme fire spread was observed on days without pyroCb activity or significant regional convection. A wide variety of ground, airborne, and satellite observations, including data collected during a major NASA airborne and field campaign, provide a unique opportunity to examine the conditions required for both extreme spread events and pyroCb development. Results highlight the importance of upper-level and nocturnal meteorology, as well as the limitations of traditional fire weather indices. The Rim Fire dataset also allows for a detailed examination of conflicting hypotheses surrounding the primary source of moisture during pyroCb development. All pyroCbs were associated with conditions very similar to those that produce dry thunderstorms. The current suite of automated forecasting applications predict only general trends in fire behavior, and specifically do not predict (1) extreme fire spread events and (2) injection of smoke to high altitudes. While (1) and (2) are related, analysis of the Rim Fire shows that they are not predicted by the same set of conditions and variables. Therefore, the Rim Fire provides an important step toward improving methodologies currently used for regional fire weather, air quality, and visibility forecasts.