Researchers are trying to shed new light on the weather patterns linked to the deaths of 19 firefighters

Yarnell Hill fire at 7:30 p.m. MST, June 29, 2013, approximately 9 p.m. before the 19 fatalities. Photo by ATGS Rory Collins.

Researchers from the Embry-Riddle Aeronautical University have published the results of their work which show that winds from a thunderstorm affected the Yarnell Hill fire. On June 30, 2013 at approximately 4:45 PM MT 19 members of the Granite Mountain Hotshots were killed as the fire changed direction and moved past their position.

The weather that led to the fatalities has been clear for approximately three hours after the burn when we reported on Wildfire Today at 7:58 p.m. MDT, June 30, 2021 before the entrapment was officially confirmed:

… It was apparently caused by a 180 degree change in wind direction. From 10 a.m. to 4 p.m. local time at the Stanton RAWS weather station four miles south of the light, the wind was blowing from the south-southwest or southwest, but by 5 p.m. it began blowing from the north-northeast at 22 to 26 mph gusting. up to 43mph. This may have pushed the fire into the city.

If there were firefighters on the south or southwest side of the fire between 4 p.m. and 5 p.m., who previously had the wind at their back for seven hours and the fire was moving away from them, they may -to be suddenly and unexpectedly found fire heading towards them at a rapid pace. Wind direction changes like this are sometimes caused by a passing thunderstorm with strong outgoing downdrafts.

And a few minutes later:

Radar 5 p.m. MDT, June 30, 2013 Pointer is in Yarnell, Arizona.
Radar 4:00 PM MST, June 30, 2013 Pointer is in Yarnell, Arizona. WeatherUnderground.

The radar map above, from WeatherUnderground, shows a thunderstorm cell to the north and northeast of the fire in Yarnell, Arizona. The pointer is in Yarnell. The cell was moving southwest and may have produced strong winds that changed the wind direction by 180 degrees and may have been part of the reason the fire moved towards Yarnell. He could also have taken the firefighters by surprise.

In 2014, an animation of the weather event was developed by Janice Coen, Ph.D., project scientist at the National Center for Atmospheric Research in Boulder, Colorado. It simulates, using a coupled weather-wildfire environment model, the spread of the Yarnell Hill fire as well as the direction and speed of the wind. The arrows indicate the direction of the wind; the length of the arrows varies with the wind speed.

Below is a summary by Ginger Pinholster of recent research conducted at Embry-Riddle Aeronautical University on the event.

Nineteen firefighters who lost their lives in Arizona’s Yarnell Hill fire in 2013 were likely victims of the same weather event that caused a fatal plane crash in 1985, Embry Aeronautical University researchers have reported. -Riddle.

City of Prescott firefighters who were members of the Granite Mountain Hotshots were likely startled by a sudden microburst during the Yarnell Hill Fire, according to Embry-Riddle meteorologists Curtis N. James and Michael Kaplan.

A microburst, and the wind shear induced by it, also knocked a commercial airliner off the runway at Dallas/Fort Worth International Airport, killing 137 people on August 2, 1985. This crash resulted in major improvements in aviation safety. The National Transportation Safety Board concluded that there was no way for the L-1011 aircraft to detect microbursts and wind shifts. In response, NASA researchers developed new warning technology, and the United States Federal Aviation Administration required all commercial aircraft to be equipped with onboard windshear detection systems.

Firefighters do not yet have equivalent protection.

Although microbursts can be detected by a Doppler weather radar scan just above the ground, radar signals are blocked in mountainous terrain or in remote areas where wildfires occur. With funding from the National Science Foundation, James and Kaplan collaborated with researchers and graduate students at North Carolina A&T University as well as the National Weather Service to better understand and learn from the Yarnell Hill fire tragedy. .

On June 28, 2013, “firefighters were aware of the squall line over the Bradshaw Mountains and its flow toward Yarnell,” said James, professor of meteorology at Embry-Riddle’s Prescott campus. “What they didn’t anticipate was that a storm cell would develop and create a microburst just east of Yarnell. We believe the flow from this microburst rushed west towards the fire, which then redirected the fire movement.

Microbursts can form very quickly around the periphery of larger, previously identified storms, explained Kaplan, associate faculty member and Embry-Riddle professor. skilled with the Desert Research Institute. “As they hit the ground, microbursts shoot outward, often at high speed,” added Kaplan, who worked on a team that studied the 1985 crash of Delta Air Lines Flight 191 in Texas.

The Yarnell Hill Fire, sparked by lightning amid drought and extreme summer temperatures, morphed in response to the flow of the microburst. The fire then quickly and unexpectedly advanced on firefighters as they tried to fight their way to safety through a ravine, James said. Analysis of historical weather data showed that the wind on the north side of the fire, at the emergency operations center, was moving from the north-northeast at 13 miles per hour (mph), while in Stanton, southeast of the fire, the wind was gusting to 47 mph.

“It was a very different situation on the south side compared to the north side of the fire,” James noted. “Small-scale convective storm cells can create this type of variability in the wind. This is something that the firefighters had not anticipated.

Stay safe on the front lines

First responders should have access to more information about microbursts, the Embry-Riddle researchers said. Even though an initial thunderstorm may appear to be fading, “it can spawn new thunderstorm cells that are extremely concentrated and intense, and sometimes incredibly small, but they can wreak havoc,” Kaplan said.

To help raise awareness of the risks of microbursts, James and Kaplan recently shared their findings at the annual meeting of the American Meteorological Society. The work was also published by the journal Weather and the review Atmosphere.

The next step in the research, Kaplan said, is to run higher-resolution model simulations coupled with a fire behavior model. If all goes well, this ‘forensic weather’ approach will show the movement of the fire as it moved through the complex terrain towards the Yarnell Hill fire department. At a resolution of 50 meters, “that would get us pretty close to the scale of what the firefighters actually saw that day,” Kaplan said. “That’s our goal.”

In addition to James and Kaplan, the research team includes Mark R. Sinclair of Embry-Riddle; North Carolina A&T State University researcher Yuh-Lang Lin and his graduate students; and Andrew A. Taylor of the National Weather Service. The research involved the use of the Cheyenne supercomputer at the National Center for Atmospheric Research and is funded by the National Science Foundation.

Thanks and hats off to Darrell.

Author: Bill Gabbert

After working full time in wildfires for 33 years, he continues to learn and strives to be a student of fire. See all articles by Bill Gabbert

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