This video shot by Big Rock Farms in Valleyford, Washington at the Yale Road Fire is an example of how a large fire whirl can very quickly spread a fire in flashy fuels.
KHQ.com described the action (you might hear a four-letter word or two):
Jay Cronk is driving a tractor through a field, attempting to lay a fire line with flames just feet away, when suddenly, the fire takes over, forcing Cronk to race away before the fire reaches the combine and the fuel tank.
Melanie Steele, Brandon Cronk and Dean Walker are the ones you hear behind the camera shouting, “Pull away! Pull away!” as they sit anxiously in another vehicle on a nearby road.
Someone also says:
You see why you don’t want to get in front of that?
The Yale Road Fire 12 miles south of Spokane forced dozens of residents to evacuate and destroyed 10 homes. As of August 25 it had burned approximately 5,791 acres. Along with the 341-acre Wellesley Fire it was part of the Spokane Complex.
Since the Beaver Creek Fire started on June 19, 2016 it has burned over 36,000 acres in northern Colorado and southern Wyoming. It is being managed by the Atlanta National Incident Management Organization (NIMO). The team described their strategy:
This is a full suppression fire utilizing both ground and aerial assets. Firefighters are engaging the fire out of the timber in areas which give them the highest probability for success. This suppression strategy provides for both firefighter safety and the protection of life and property.
After almost two months, the team claims 44 percent of the perimeter has been contained. They expect full containment on October 21 (the year was not specified). It sounds like they may be stretching the definition of “full suppression”. So far they have spent $20,600,000 of taxpayers’ money.
Here is another photo from the fire. Found on InciWeb, it is undated and uncredited.
These two recently filmed videos illustrate what can happen over a fire when thermal instability and available vorticity combine.
The Cornelius (Oregon) Fire Department posted this video on August 12, 2016 showing an impressive fire whirl.
The video below was filmed by Stewart Turner August 5, 2016 on the Pioneer Fire in Idaho. You will see a definite rotation, or convection column vortex. While this one is not as violent as, say, a conventional tornado, the change in wind direction or the collapse of the column can cause a serious problem for nearby firefighters.
The news media sometimes calls any little fire whirl a “fire tornado, or even a “firenado”. We found out today that these and related terms (except for “firenado”) were, if not founded, at least documented and defined in 1978 by a researcher for the National Weather Service in Missoula, David W. Goens. He grouped fire whirls into four classes:
Fire Devils. They are a natural part of fire turbulence with little influence on fire behavior or spread. They are usually on the order of 3 to 33 feet in diameter and have rotational velocities less than 22 MPH.
Fire Whirls. A meld of the fire, topograph, and meteorological factors. These play a significant role in fire spread and hazard to control personnel. The average size of this class is usually 33 to 100 feet, with rotational velocities of 22 to 67 MPH.
Fire Tornadoes. These systems begin to dominate the large scale fire dynamics. They lead to extreme hazard and control problems. In size, they average 100 to 1,000 feet in diameter and have rotational velocities up to 90 MPH.
Fire Storm. Fire behavior is extremely violent. Diameters have been observed to be from 1,000 to 10,000 feet and winds estimated in excess of 110 MPH. This is a rare phenomenon and hopefully one that is so unlikely in the forest environment that it can be disregarded.
Mr. Goens further described three different types of fire whirls generated:
The Thermally Driven Form. This results from some type of shear in the horizontal airflow coupled with the energy release (convection) from fire activity.
The Convection Column Vortex. This form is poorly understood. It originates high in the convection column (up to 1000 feet) and extends in the ground as much as a fourth (1/4) mile on the leeward side of the fire.
The Wake-Type Whirl. This results from the generation of eddies caused by airflow around an obstacle coupled with heat released by the fire.
Mr. Gowns continued:
All three of these types can be a significant problem in the spread or control of fire. The fire whirl in its steady-state form, i.e., after it has formed and before it begins to collapse, has two sharply defined regions of differing airflow (Byron and Martin 1970). The cooler, slowly rotating zone surrounds a central core of hot gases with high horizontal and vertical velocities. This central core can have temperatures from 1,800° to 2,400°F and burning rates two to seven times normal. Flame height can be 10 to 50 times the core diameter. Fire spread occurs when burning debris entrained into the column just above the surface boundary layer is carried aloft and then cast out from the upper portion of the whirl core some time later. The path of the whirl can be quite erratic; therefore, direction and rate of spread are almost impossible to forecast.
One of the best videos of a large fire whirl or fire tornado was shot by Chris Tangey of Alice Springs Film and Television in 2012 while he was scouting locations near Curtin Springs station in Australia. It is used here with his permission.
And lastly, I filmed this next video at the USFS Fire Lab in Missoula in 2014, showing an artificially created fire whirl.