Meteorological Conditions and Decision Support Services Associated With the Yarnell Hill Fire

The Yarnell Hill Fire is most well-known for the tragic deaths of nineteen members of the Granite Mountain Hotshots team of wildland firefighters. Though thunderstorm outflow was the most obvious factor leading to extreme fire behavior at Yarnell Hill, several other meteorological factors contributed to the rapid intensification of the fire. In the longer-term, the condition of vegetation in the Yarnell area was strongly influenced by drought. In the shorter-term, June 2013 in the Yarnell area concluded with several days of record to near-record high temperatures. Late in the morning on 30 June, thunderstorms forming over the Mogollon Rim generated a large-scale outflow boundary which moved southwestward into Yavapai County by afternoon. Strong storms developed along the boundary near the Bradshaw Mountains southwest of Prescott, likely enhancing the outflow as it continued southwestward toward Yarnell. These strong storms rapidly dissipated between 2200-2300 UTC, likely further influencing outflow strength, speed, and duration.

The National Weather Service (NWS) Flagstaff Forecast Office exercised several opportunities to provide decision support to key partners both leading up to and during the Yarnell Hill Fire. Several days prior to the fire's lightning-caused ignition, a high-impact weather briefing was provided to all emergency management and first responders email lists discussing near record high temperatures and possible thunderstorms contributing to extreme fire behavior during the upcoming weekend. On the afternoon of 30 June, two phone calls were made to dispatch at the Yarnell Hill Fire. A call at 2105 UTC alerted them to new convection developing near and east of the fire and associated strong/gusty winds. The next call, at 2230 UTC, provided information regarding the approaching wind shift and estimated speeds. Phone calls to the Yarnell Hill dispatch resumed in the late evening as another wind shift approached the fire from the southeast.

The Yarnell Hill Fire tragedy highlights the need for both scientifically sound forecasts and clear, timely communication of forecast information. Both points will be emphasized.