Weather a Factor in Deadly Arizona Fire

By: Jon Erdman
Published: July 12, 2013

While the Desert Southwest was searing in record heat and has been suffering from a long-term drought, shifting winds from thunderstorms appear to have turned a wildfire near Yarnell, Ariz. into a tragedy Sunday, June 30.  

(LATEST NEWS:  Deadly Arizona Wildfire)

Yarnell Hill Fire Radar Summary

Radar Loop: Yarnell Hill Fire Tragedy

Animation of radar and lightning strikes from 2pm to 6pm MST on Sunday, June 30, 2013. Location of the Yarnell Hill fire is plotted.

According to the incident report from the National Interagency Fire Center issued Sunday, firefighters were working to secure the eastern flank of the Yarnell Hill fire to protect homes at risk.  Evacuation orders were issued in the towns of Yarnell and Peeples Valley, about 85 miles northwest of Phoenix.

At right is a radar loop from 2-6pm MST over central Arizona.  Typical of the summer months, a line of thunderstorms formed over the Mogollon Rim in early afternoon and swept southwestward toward the lower deserts, producing little rainfall, but instead strong, shifting outflow winds.  Here's a breakdown of the winds, utilizing surface observations from Prescott, Ariz., about 40 miles northwest of Yarnell.

  • 2:24 p.m.:  Thunderstorm observed east of Prescott produces ESE wind gust to 22 mph in the city.
  • 2:37 p.m.:  A peak ESE wind gust to 39 mph is measured in Prescott.  
  • 2:53 p.m.:  Winds shift to SSE gusting from 25-35 mph in Prescott as line of t-storms shifts to the south of the city, moving toward the Yarnell Hill fire.
  • 3:53 p.m.:  Winds shift to WSW gusting to 21 mph at Prescott.  This westerly wind shift will be important later.
  • 4:47 p.m.:  Peak WSW wind gust to 44 mph is measured.
  • 5:53 p.m.:  WSW winds still gusting to 22 mph.
  • 6:53 p.m.:  Calm winds reported.
  • Total rainfall:  0.01"

Another wind sensor located near the town of Peeples Valley indicated an opposite wind shift, from the west-southwest to the north-northeast as the line of t-storms appeared to collapse near the fire after 4 p.m.  The general layout of the terrain in a bowl-shaped valley opening toward the northeast likely enhanced wind speeds.  

This chaotic shift in wind direction, almost 180 degrees difference from what had been measured just over an hour earlier, not to mention the strong outflow gusts, would be exceedingly difficult to forecast and hard for firefighters in the field to quickly react to.  Notification that fire shelters were deployed was received by a fire dispatch center around 4:50 p.m., according to Carrie Dennett, from the Arizona State Forestry Division.   

You can see the effect of the shifting winds on the fire's behavior in this short YouTube from Matt Oss, filmed near Congress, Ariz., southwest of Yarnell.  Around four seconds into the video, you'll notice a blast of wind-blown dust near the bottom of the video.  At ten seconds in, you'll see flames nearing the crest of the mountain with a plume of smoke blowing down the mountain toward you.

In just over 12 hours, the fire size more than quadrupled, from 2000 acres to 8300 acres, as of early on July 1. 

This is eerily reminiscent of the rapid growth of the Waldo Canyon Fire near Colorado Springs almost one year prior.  Shifting, high winds from nearby, dying thunderstorms directed the inferno into the far northwest side of Colorado Springs in late June 2012, destroying 347 homes and killing two.  

MORE:  Photos of Yarnell Hill Fire

Brendan McDonough, the only surviving member of his crew, receives a hug from Vice President Joe Biden during the "Our Fallen Brothers" memorial servicein Prescott Valley, Ariz. on July 9, 2013. (AP Photo/The Arizona Republic, David Kadlubowski , Pool)

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