Weather Forecasts and The Yarnell Hill Fire: Modest Reflections on Knowing What We Know and Acknowledging What We Don’t

Working on wildland fires is inherently risky. Fire is dangerous, it can kill, and it is as unpredictable as a captive orca, particularly as the size of the fire increases and the relevant terrain becomes more uneven. Therefore, it is important to learn as much as possible from each and every mass tragedy involving wildland fire, so that future generations of wildland firefighters can better protect themselves.

Part of learning from tragedies on wildland fires involves figuring out – in as much detail and with as much precision as possible – what went wrong or occurred leading up to the tragedy, so that similar factual scenarios in the future can be made safer. If a wildland fire tragedy is blamed on a predicted weather event – such a forecasted wind shift – when that predicted weather event was not actually the direct causal factor of the tragedy (or it wasn't the causal factor in the way the prevailing narratives suggest), the fireline is actually made even more dangerous, because wildland firefighters will inappropriately take comfort in remedial measures such as more frequent forecasts or an IMET on every fire over a certain size. Phrased differently, inaccurately blaming a wildland fire tragedy on a predicted weather event is dangerous, because it diverts focus – and safety measures – from wherever they should be focused instead.

In the wake of both the South Canyon Fire and the Yarnell Hill Fire, seasoned wildland fire investigators and expert wildland firefighters pointed their fingers at a forecast weather event (an “outflow boundary,” arriving from the N/NE, with winds up to 40 mph, in the case of the Yarnell Hill Fire) as the direct causal factor in the fire blow-up, direction change, and exponential increase in rate of spread that then entrapped and killed dozens of wildland firefighters. The “eruptive fire behavior” (or blow-up) in the South Canyon Fire or the Yarnell Hill Fire that ultimately entrapped and killed dozens of wildland firefighters was assumed to be the product of high-speed winds that were pushing the fire on top of the wildland firefighters faster than they could outrun it.

But roughly ten years after the 1994 South Canyon Fire tragedy, a fire scientist named Dr. D.X. Viegas started publishing essays in which he suggested that the “predicted wind event” narrative does not accurately explain what happened with the South Canyon Fire in the minutes leading up to the entrapment and deaths. Viegas observes that there was no wind event of the sort that National Weather Service meteorologist Chris Cuoco predicted that pushed the fire directly on top of the deceased wildland firefighters. If the weather event had any sort of impact, it was far more subtle, more nuanced, less direct, far less obvious (particularly to those on the ground, working on the fire line), and harder to figure out. In Viegas's view, the South Canyon Fire blow-up (and the resulting tragic deaths) was the product of uber-extreme fire behavior creating its own influencing forces, particularly when coupled with sloping terrain. Convection, indrafting, and a positive feedback cycle appear to be what Viegas would finger as the causal factor of the South Canyon Fire, moreso than meteorologist Chris Cuoco's forecasted weather event.

The same case can be made regarding the Yarnell Hill Fire. In the wake of the tragic fire on June 30, 2013, multiple expert investigation teams and multiple meteorology academics and professionals indicated that 19 Granite Mountain Hotshots died at the Yarnell Hill Fire because of a predicted weather event (winds from an outflow boundary, arriving from the N/NE at speeds of up to 40 mph) that pushed the fire on top of the hotshots.

But the time-stamped photos and videos do not support this narrative. There is no evidence in the local communities of outflow boundary winds from the N/NE of up to 40 mph. Lawn furniture was not strewn, camera tripods were not knocked over by 40 mph winds, people did not have trouble walking into the alleged wind. Moreover, the fire eruption that ultimately entrapped and killed the Granite Mountain Hotshots appears to have come from the west/NW. If there were direct outflow boundary winds of up to 40 mph from the N/NE, the fire would have been pushed to the South/SW and away from the Granite Mountain Hotshots. But that is not what happened.

In this presentation, a more accurate timeline and relevant photos will be presented, to assess how they line up with the presumed wind event, and relevant operational take-aways (such as the need to acknowledge that even the best, most accurate weather forecast might not be able to be linearly used in predicting in detail short term wildland fire behavior) will be discussed.