The role of convective outflow in the Waldo Canyon fire

The meteorological conditions associated with the rapid intensification and spread of the catastrophic Waldo Canyon fire on 26 June 2012 are studied. The fire caused two fatalities, destroyed 347 homes in Colorado Springs, and resulted in insurance losses of nearly $0.5 billion (U.S. dollars), making it the most economically destructive fire in Colorado's history. While the fire was first discovered on 23 June, the paper focuses on 26 June, when it grew explosively and rapidly advanced eastward into a heavily populated area on the west side of Colorado Springs. Near-record hot and dry conditions prevailed over the Intermountain West prior to the fire, along with a persistent upper-level ridge. On 26 June, a narrow tongue of moist air aloft originating over the Southwest shifted from Utah into Colorado. Dry conditions at low levels and moisture aloft set the stage for strong microburst-producing thunderstorms to develop over Colorado. Convective cells first formed at midday over the San Juan Mountains, later consolidating into a thunderstorm complex that produced an organized convective outflow with strong, gusty winds at the surface. The leading gust front associated with the outflow moved past the Waldo Canyon fire at the hottest time of the day with recorded wind gusts up to 26 ms^-1. The rapid eastward advance of the fire, as well as an onset of pyrocumulonimbus and lightning activity, was timed with the passage of the gust front. A numerical simulation, initiated one day earlier, produced mesoscale features closely resembling those observed, including the gust front passage at the fire and the vertical structure of the convective outflow.