The Yarnell Hill Fire: Microbursts, Density Currents, and 19 Lost Lives

A Research Spotlight from the 14th Annual Fire and Forest Meteorology Symposium, 2–4 May, 2023

The Yarnell Hill Fire the day it began, June 28, 2013. Image credit: USDA

Arizona’s Yarnell Hill Fire ranks among the U.S. wildfires with the most firefighter fatalities. On June 30, 2013, members of the interagency Granite Mountain Hotshots were entrapped in a canyon by fire due to rapidly shifting wind conditions. Many attempted to take shelter but were overwhelmed. Nineteen firefighters died and the fire, fed by the strong winds, blazed out of control. The tragedy and damage devastated the community of Yarnell, Arizona.

A joint team at Embry-Riddle Aeronautical University and North Carolina A&T State University has been using simulations to help understand exactly what happened. A recent presentation by Michael Kaplan et al. May 2, 2023 in the first session of the 14th Fire and Forest Meteorology Symposium broke down the events at the meso-γ (2–20 km) scale leading up to the tragedy, the latest in a series of analyses starting at large scales and moving towards ever-finer resolution. They found that a density current (a flow of denser air that intrudes underneath less-dense air) and its secondary circulations drove the winds that forced fire into the canyon where the Granite Mountain Hotshots were located.

Firefighters near the Yarnell Hill Fire on June 28, 2013. Image credit: USDA

A squall line that developed over the Colorado Plateau on the morning of the 30th moved southwestward rapidly, strengthening over the Black Hills and Bradshaw Mountains on the way, until it died out further to the southwest over the Weaver Mountains near Yarnell. From this dying squall line developed a density current that produced unusual air circulation patterns in combination with the area’s complex terrain. Simulations by the Weather Research and Forecasting (WRF) model suggest that the fading density current created conditions in the Weaver Mountains that were highly conducive to downward air motion. This resulted in a series of strong localized downdrafts similar to microbursts near the fire site.

Earlier in the day, the fire had been moving towards the northeast, driven by southwesterly winds. Within 1–2 hours in the late afternoon, the winds shifted and intensified rapidly, becoming northwesterly, then northeasterly, blowing at 45 miles per hour and driving the fire (now blazing at 2,000 degrees Fahrenheit), in a southwesterly direction. Kaplan called these shifts “dramatic, remarkable changes.”

Wind direction and speed (blue arrows) and direction of Yarnell Hill fire motion (red lines) at 3:30–4:30 p.m. and 4:30–5:30 p.m. local time on June 30, 2013. Image: State of Arizona Serious Accident Investigation Team

In the end, “The entrapment of the Granite Mountain Hotshots was likely the result of very, very intense redirected winds” that continued over a longer than expected period, Kaplan said. “Even after they got the initial surge of northeasterly flow [due to the density current] the Hotshots had to deal with more surges of high momentum” from the series of microbursts. He noted that despite the Granite Mountain Hotshots’ high level of experience, “This is something firefighters may not have really been [expecting] to occur.”

Vertical cross-section of potential temperature and isotachs from 3:15 to 3:35 p.m. Arizona time on June 30, 2013, showing new cells forming behind the density current near Yarnell, associated with microburst downdrafts. Image courtesy of Michael Kaplan

Kaplan’s team will continue to work on their simulations of conditions associated with the Yarnell Hill Fire, with the hope of providing information that can help prevent similar entrapments, and deaths, in the future.

Meeting registrants can view the recording of this session here. Recordings become publicly available three months after the meeting.


About 14Fire
Meteorology and wildfires are intimately interconnected—and wildfires are becoming increasingly severe and frequent in many parts of the United States. From local residents and firefighters on the ground to planners and insurers, to people hundreds of miles away breathing wind-driven smoke, society relies on our ever-improving ability to understand and forecast the atmospheric conditions relating to wildfire. The American Meteorological Society’s 14th Fire and Forest Meteorology Symposium brought together researchers and fire managers to discuss the latest science.

Moving Mountains, Not Meteorology

If you attended the joint AMS conferences—on Applied Climatology and on Meteorological Observation and Instrumentation—held in the shadow of Colorado’s Rocky Mountains last week, you encountered the rich diversity of presentations encapsulating the topics that preoccupy specialists these days.
You heard lessons learned from using familiar tools of the trade, the latest news about new technology, ways of observing drought, impacts of El Niño, and principles of wildfire management.
There was much advice about communicating to the public about climate change, and about the scientific basis presented by the National Climate Assessment. You heard advice from the folks at Climate Central. You delved into how to handle information delivery in the duress of extreme events.
If you’ve moved on to California this week for the AMS Conference on Broadcast Meteorology at Squaw Valley, you enter a different world, right? From the dark, craggy jumble of Precambrian sediments, granite, and gneiss, you’re now surrounded by the pale glow of Sierra Nevada granite. And from scientists focused on research, now you’re in the realm of communicators bringing science to mass media.
So, you’ll hear lessons learned from using familiar tools of the trade, the latest news about new technology, ways of observing drought, impacts of El Niño, and principles of wildfire management.
There will be much advice about communicating to the public about climate change, and about the scientific basis presented by the National Climate Assessment. You’ll get some advice from the folks at Climate Central.  You’ll also delve into how to handle information delivery in the duress of extreme events.
Déjà vu? Copy-and-paste error?
No. For all the specializations and variations in interests that collectively constitute the American Meteorological Society, there’s a lot in common between even the seemingly disparate branches. The roots in science grow into all sorts of permutations. The mountains may shift, but that’s a mere backdrop for the constancy of meteorology and related sciences flourishing across the land.
Enjoy your meetings.

Vortex Delight

This Monday at the AMS Conference on Mountain Meteorology, Rieke Heinze of the Institut für Meteorologie und Klimatologie at the Leibniz Universität Hannover presented this very cool looking simulation of von Kármán vortex streets, which sometimes show up in satellite images of clouds in the lee of isolated mountain islands. The nifty thing about Heinze’s simulation project is that it shows the vortices retaining a warm core from bottom to top in the flow (cross section not shown here).
On her project web site (where you can download the video), Heinze writes:

Atmospheric vortex streets consist of two rows of counterrotating mesoscale eddies with vertical axis in the wake of large islands. They resemble classical Kármán vortex streets which occur in laboratory experiments behind a cylinder. Usually, atmospheric vortex streets can be found in the stratocumulus capped mixed layer over the ocean when there is a strong elevated inversion well below the island top.

In the animations the island consists of a single Gaussian shaped mountain with a height of about 1.3 km and a base diameter of about 12km. Particles are released in one layer and act as passive tracers. Their vertical motion is disabled. The colour of the particles reflects the difference between the temperature at the respective particle position and the mean temperature, horizontally averaged over the total domain. Blue/red colours represent a relatively low/high temperature. The animation shows that the cores of the eddies are warmer than the environment. The length of the animation corresponds to about 14h real time.