Weather forecast for the prescribed fire in Arizona that led to accidents on Interstate 40

prescribed fire smoke accidents arizona
Map, produced at 11:41 a.m. MDT Oct. 20, 2016, showing heat detected on the Green Base prescribed fire. The dots nearest the Interstate represent heat that was detected during the afternoon of October 18, 2016. The northernmost dots are from October 17, 2016. Click to enlarge.

We looked further into what led to the smoky conditions that resulted in numerous vehicle crashes on Interstate 40 west of Flagstaff, Arizona early Wednesday morning, October 19. The smoke on the highway from a prescribed fire was referred to as “pea soup”, and was clearly the cause of some of the accidents, but investigators are not yet ready to say the smoke caused the one fatality when a vehicle was sandwiched between two semi trucks.

During the very early morning hours of Wednesday, October 19, smoke settled into the areas around Interstate 40 between Parks and Williams. An electronic sign warned motorists about smoke, but the severely reduced visibility was not anticipated by the U.S. Forest Service. After the accidents started occurring the Interstate was closed for five hours.

ADEQ smoke permit green base prescribed fire
Data from the smoke permit issued by the Arizona Department of Environmental Quality for the Green Base prescribed fire. Click to enlarge.

The Kaibab National Forest ignited the Green Base Prescribed Fire on Tuesday, October 18, 2016 immediately north of Interstate 40. The smoke permit issued by the Arizona Department of Environmental Quality anticipated moderate “impacts on sensitive areas”:

Smoke impacts to the following communities of Flagstaff, Parks, Spring Valley, Pittman Valley, Sherwood Forest Estates and some smoke may impact Williams. I-40 may experience moderate smoke impacts in low-lying areas.

The Flagstaff office of the National Weather Service issued a Spot Weather Forecast for the Green Base Prescribed Fire at 5:28 a.m. MST on Tuesday October 18, 2016. It anticipated a “good” maximum ventilation rate for Tuesday, did not specify one for Tuesday night, and for Wednesday it was described as “fair”.

spot weather green base prescribed fire
Spot Weather forecast for the Green Base Prescribed Fire, October 18, 2016. Click to enlarge.

The ventilation rate provides an estimate of how high and how far smoke will disperse. A high ventilation rate suggests that smoke will spread out quickly and through a deep layer of the atmosphere, so that surface concentrations downwind will be lower than they would be with a lower ventilation rate.

The transport winds (from the ground to the mixing height) for Tuesday night were predicted to be “west 5 to 10 knots shifting to the north after midnight, then shifting to the northeast early in the morning.” The wind speed after the shift was not specified. Perhaps this was interpreted by fire managers to mean it would continue at 5 to 10 knots.

The prescribed fire was just north of the east-west Interstate, so a wind out of the northeast would likely push the smoke toward the highway. And if an area is prone to nighttime inversions, visibility can be compromised.

Fox News reported that Cory Mottice, a National Weather Service meteorologist in Flagstaff, said, “[Smoke] always gets trapped after dark,” he said. “It’s just a question of where the wind blows it.”

However that analysis was not described in detail in the spot weather forecast issued by Mr. Mottice’s office. As in many spot weather forecasts, much of the information appears to be generated by a computer, with little interpretation or discussion about how the information will affect the fire. Meteorologists are not expected to be Fire Behavior Analysts, but sometimes a little human-created discussion and interpretation can add value to a computer product.

Below are excerpts from an article at the Arizona Daily Sun:

… A Highway Patrol captain at the scene said smoke in the area reduced visibility down to about 20 feet, Department of Public Safety spokesman Bart Graves said. Sherwood Forest Estates Fire Chief Wayne Marx said even his crews had to stick their heads out the window to watch the yellow stripe on the road as they escorted commuters away from the interstate.

“You couldn’t see past the end of the hood,” Marx said.


One retired meteorologist who lives in the area believes more precautions should have been taken. Parks resident Byron Peterson, who retired from National Weather Service station in Bellemont, said the smoke was already bad on Old Route 66 Tuesday afternoon. Firefighters waved him on, he said, even though there were times when he could not see 10 feet in front of him.

“It was very frightening to say the least,” Peterson said.

He said strong southwest winds coming up over Bill Williams Mountain near Williams formed an eddy of swirling air that then dove down over the prescribed burn, keeping the smoke from dissipating.

“I tried to explain that to people at the Forest Service and it was just like talking to a wall,” he said.


Interstate highway closed after accidents caused by prescribed fire smoke

Investigators will determine if poor visibility was the cause of a fatal accident.

Above: Vehicles at the scene of an accident on Interstate 40 Wednesday, October 19, 2016. Photo by Arizona Department of Public Safety.

(On October 20 we wrote a follow-up article about this incident which looks at the weather forecast and the smoke permit that preceded ignition of the prescribed fire.)

After numerous accidents occurred in thick smoke from a prescribed fire, authorities closed Interstate 40 west of Flagstaff, Arizona on Wednesday. The Kaibab National Forest conducted the burn Tuesday and knew that a wind shift would push the smoke toward the interstate, but they were surprised that the smoke settled near the ground early Wednesday morning rather than being moved out of the area. Electronic signs warned drivers about the potential hazard.

Below is an excerpt from Fox News:

Multiple collisions with minor injuries to motorists and passengers were blamed on smoky haze that settled over the highway for about five hours. Authorities closed I-40 for hours to prevent more accidents.

Police had not immediately determined whether the poor visibility was the cause of a fatal accident after a vehicle was sandwiched between two tractor-trailers before dawn, said Arizona Department of Public safety spokesman Bart Graves.

But the area at this time of year experiences temperature inversions allowing smoke to be trapped close to the ground and hover over the highway, said Cory Mottice, a National Weather Service meteorologist in Flagstaff.

“It almost always gets trapped after dark,” he said. “It’s just a question of where the wind blows it.”

Forest officials thought weather conditions would vent smoke near the freeway more than it did in low-lying areas, Smith said.

“I believed they used good judgment based on the conditions and the information that they had,” said Brady Smith, a U.S. Forest Service spokesperson.

Sequoia NP reintroduces fire where it had been excluded for decades

This week the National Park Service reintroduced fire to an area in Sequoia National Park where it had been unnaturally excluded for decades. The 187-acre Dorst prescribed fire near Dorst Campground is expected to help restore a more natural density of fuels and vegetation.

All photos were provided by the NPS.

Dorst prescribed fire Sequoia National Park
Dorst prescribed fire, October 10, 2016. NPS photo.

Dorst prescribed fire Sequoia National Park

Pile burning on the Beaverhead-Deerlodge NF

Over the last week Derek Wittenberg has been working with his colleagues on the Beaverhead-Deerlodge National Forest in western Montana (map) burning piles that were created while building a fuel break on the Pole Fire. Other piles were part of a project to promote a Whitebark Pine stand that is resistant to Blister Rust.

He posted photos and videos on his Instagram page that are used here with his permission.

Piles like these are often burned while there is snow on the ground in order to minimize the chance of the fires spreading out of control. Some of the keys to success are constructing the piles so that some material remains relatively dry even after rain or snow, and using firefighters that are skilled with a drip torch.

The crew took advantage of the opportunity to conduct training with a Very Pistol.

Veri pistol training and pile burning

A photo posted by Derek Wittenberg (@ridebigmtn) on


A video posted by Derek Wittenberg (@ridebigmtn) on

Continue reading “Pile burning on the Beaverhead-Deerlodge NF”

Minam prescribed fire in northeast Oregon escapes control

Above: Minam Fire, Friday September 30, 2016. USFS photo.

A prescribed fire on the Wallowa-Whitman National Forest escaped the day after it was conducted in northeast Oregon. The 2,000-acre project was ignited with a helicopter on Thursday, September 29 as a continuation of previous prescribed burning activities in the Minam drainage within the Eagle Cap Wilderness Area about 21 miles northeast of La Grande, Oregon.

Late in the afternoon of the next day, Friday, during a helicopter flight to check the status of the project, fire managers found a spot fire east of the burn area across Trout Creek. Due to the time of day, it was determined that firefighters could not safely access the spot fire until the following day.

Map Minam Fire
Map of the Minam Fire, October 3, 2016, showing heat detected by satellites over the previous several days.

Early Saturday, October 1, a powerful thunderstorm moved through the area bringing stronger than expected winds and very little moisture. As planned, firefighters hiked into the spot fire on Saturday and found that the winds had spread the spot fire to the east, upslope onto Cougar Ridge, and ultimately outside the planned prescribed fire area.

The Minam Fire was declared an escape Saturday afternoon, October 1st, when fire managers determined that they would not be able to contain the portion of the fire that had spread outside of the planned perimeter within the next 24 hours, which is a criteria for declaring an escaped prescribed fire.

Cooler weather kept the spread of the fire minimal into Sunday as additional crews and aircraft arrived on scene to support the suppression efforts.

As of Sunday, October 2, the escaped fire had burned 750 acres.

Researchers study how to reduce soot produced by agricultural fires

agricultural burning smoke
Smoke plume from the burning of wheat residue on the Nez Perce Reservation. The field was burned using a head fire. The dark color of the smoke plume indicates high soot content. Photo by Emily Lincoln.

The production cycle of cereal crops and grasses in many areas of the United States includes burning fields of post-harvest residue such as wheat stubble. Like smoke from forest fires, smoke produced by agricultural burning can have harmful effects on public health.

The U.S. Forest Service and the Washington State Department of Ecology conducted a study to determine the effects different ignition tactics had on the smoke produced by agricultural burning of wheat residue.

agricultural burning smoke
Smoke plume from the burning of wheat residue north of Walla Walla, Washington. The field was burned using a backing fire. The light color of the smoke plume indicates low soot content. Photo by Emily Lincoln.

They found that smoke plumes produced from burning wheat residue using head fires contained more soot than plumes produced using backing fires.

Soot particles are black aerosols composed primarily of elemental carbon. The World Health Organization reports that soot particles may have significantly greater negative health impacts than other particle types found in smoke and air pollution since these particles can act as a carrier for toxic combustion-derived chemicals.