Vertical meteorologist Ed Brotak takes a look at the hazards firefighting pilots encounter, and explores various fire-induced weather phenomena.

As wildfires begin to be something of a year-round hazard for hotspots around the world, the spotlight on safety in aerial firefighting operations is increasing in intensity. Understanding wildfire behavior is a key element to safe operation, and to best understand wildfire behavior, you need to know how various weather conditions impact wildfires.

Specific wildfire weather elements are provided by government meteorological services. Helicopter pilots working a wildfire will check these wildfire weather forecasts, as well as following their own individual routine for getting weather information prior to takeoff.

Significant fires require a multifaceted response directed from a command center, typically located close to the fire site. In an almost military-type operation, both land crews and aerial support will be engaged in the control effort. Note that the goal is not to put out a fire, but rather to contain it and let it burn itself out. Each morning, briefings are held to describe current and expected conditions, and to outline a plan of attack. The expected weather conditions are always highlighted.

Aerial operations (or air ops) will have their own briefing, with special emphasis on the weather conditions that will affect aircraft assignments. According to Brandon Culley, the unit aviation officer at Malheur National Forest in Oregon, such briefings will cover “weather parameters such as wind, temperature — used for performance planning, visibility, how the fire will be affected by the wind, and humidity. Also of concern for pilots [is] critical low-level winds and topographic winds.”

For major fires in the U.S., Canada, and Australia, the government will send a meteorologist to provide onsite weather information for the fire. In the U.S., the National Weather Service will assign an incident meteorologist (IMET). These IMETs, besides being highly trained, experienced meteorologists, have also gone through special training for wildland fires.

Andy Gorelow is an IMET stationed in Las Vegas, and has worked on over 20 fires — many in California. “Sometimes we do give aviation briefings directly to the pilots,” he said. “The pilots were interested in cloud heights [ceilings], temperatures at 5,000 and 10,000 feet, surface visibility, and winds. A lot of the information I gave came from local soundings. I launch weather balloons on a fire to gain a lot of this information if I am not close to an Upper Air [Observation] Site.”

Conditions to consider

What weather conditions most impact pilots when fighting wildfires?
Mel Ceccanti, director of flight operations, rotorcraft, at Coulson Aviation, highlighted the challenge posed by wind. “Strong winds with moderate or greater turbulence may be outside aircraft limitations,” he said. “In the worst case, it can produce aircraft damage. Aircraft being grounded due to strong winds happens all the time.”

Ceccanti relates a particular case two years ago in Orange County, California. “With winds well in excess of 40 knots, even though we knew the fire would get big, we had to shut down air ops at 11:30 a.m. — the turbulence was too extreme.”

Wind can also affect how you attack a fire, Ceccanti said. “The wind affects the fire and the flight path, [as] we prefer to drop into the wind. And for water drops, high winds can make it difficult to get water to the ground.” And mountainous terrain only increases turbulence.

The interaction of wind and smoke are also important. Mark Wiskemann, president and ops manager of Wisk Air Helicopters, has worked on hundreds of fires over a 40-year career. He highlighted the impact of wind on visibility. “Winds blow smoke away, while calm conditions are the worst for smoke.”
Brent Keeler, a utility pilot and check airman at PJ Helicopters who has flown a variety of helicopters on fires since 2006, agreed that wind and smoke are major concerns. Fires with heavy smoke can create major visibility issues, he said. The potential danger is enhanced when helicopters “sometimes fly at tree top level” and “with multiple helicopters in the sky at the same time,” he added.

Keeler also noted the role of inversions, which occur when air temperatures increase rather than decrease with height. “Inversions can create dense smoke and limited visibility,” he said. The top of the inversion layer acts as a lid, preventing winds aloft from reaching lower levels. Typically, they form at night and dissipate in the morning with daily heating.

IMET Gorelow said the “number one” question he receives from pilots is when an inversion will lift and the smoke will clear.

Lachie Onslow, chief pilot and director of Fleet Helicopters, has worked on hundreds of fires over the past 30 years. “Loss of visibility, [and] becoming trapped or being forced into the low level power line environment due to smoke can catch a pilot out,” he said.

Another threat brought up by Keeler is the impact of storms. “It doesn’t come up on a daily basis, but thunderstorms and hail are a major concern,” he said. “It requires a bit of planning to get aircraft out of the area if hail and extreme winds are forecast — and these storms often develop quickly, making pre-planning a contingency plan difficult.”

Ceccanti agreed about the thunderstorm risk. “Lightning is a major concern, since most helicopters are not designed to be hit by lightning. Avoid it at all costs.”

Occasionally adding to the problem are “strong winds and turbulence from an approaching storm, [which] may be hidden by smoke,” said Onslow.
In terms of using weather in your favor, Ceccanti said that Coulson Aviation’s ability to fight fires at night presents many benefits. “Winds typically die down [at night] and humidities will increase,” he said. “Water/retardant doesn’t evaporate as quickly, and so it has a much greater impact on fire at nighttime. The effectiveness of water drops increases 60 percent at night.” When the company performed a night attack on the Orange County fire after winds had precluded daytime operations, Ceccanti said, “We absolutely smashed it; [it was] very successful.”

Fire-induced Weather

If the overall weather conditions aren’t enough to deal with, firefighters may have to contend with “fire-induced weather.” This is especially true if the fire develops a significant convective column and becomes a “plume-dominated fire.” This typically occurs when ambient winds aren’t that strong and there is a considerable fuel load. The heat generated by the fire will send a column of super-heated air upward into the atmosphere. Convective columns can rise to 40,000 feet.

The rising air will cool, and condensed water vapor can form a true cloud — a “pyrocumulus cloud” — over the fire. Sometimes, this fire-produced cloud can produce rain and even lightning. Downdrafts in the cloud can reach low levels causing problems.

A particularly dangerous time, according to Ceccanti, is when you have “collapsing columns” over a fire. And as David Sewell, chief pilot with Kestral Aviation, said, “Our pilots are well advised to remain clear of the head of the fire when the pyrocumulus cloud falls upon itself in the late afternoon.” When the convective column collapses, a great outrush of air can occur at low-levels, producing very strong winds in different directions and extreme turbulence.

Among the most spectacular — and often dangerous — fire-induced elements are the various fire vortices. All are produced by rapidly rising, superheated air with rotation. “Fire devils” are small, only feet in diameter, and are typical with any fire. “Fire whirls” are larger — tens of feet across — and can move away from the parent fire, posing considerable risk to firefighters.

True “fire tornadoes” are much larger — hundreds of feet in diameter — and have considerable vertical height. They are also much stronger, with winds that can exceed 100 mph (160 km/h). These are tied in with the convective column of the fire, much the same way a typical tornado is associated with a parent thunderstorm. On July 26, 2018, the Carr Fire in Shasta County, California, rapidly developed a massive convective column that rose to 40,000 feet. A half-mile-wide fire tornado developed at the surface with wind speeds estimated at 140 mph (225 km/h), and it did considerable damage to the town of Redding.

Most pilots who fight wildfires have seen fire vortices. “They are completely unpredictable and can pop up out of nowhere,” Ceccanti said, “but they are not a huge threat to aircraft, as you can see them and fly around them.”
Brent Keeler said he has also seen fire whirls. “The fire is usually so intense in those areas that we keep our distance,” he said.

How would these pilots sum up dealing with wildfire weather conditions? Kestrel’s Sewell said his company’s pilots are kept well updated on daily weather and fire events. “We train our pilots to recognize the threats the fire and associated weather produces, and the necessity sometimes to sit out a weather event or a substantial fire thrust,” he said.

Ceccanti said you can never afford to push weather limits. “There are a lot of things going on rapidly — changing missions, changing conditions, winds, temps, turbulence, terrain, smoke, etc.,” he said. “It’s just not very forgiving — you have to be well ahead of the aircraft and your situational awareness has to be on point.”

Finally, what does the future hold in terms of fighting wildfires? “Although there are seasonal variances, there has been an increase in the number of fires and a really quite noticeable increase in the intensity of fires,” said Wiskemann.

Ceccanti concurs: “In general, the number of fires seems to only grow every year of the 20 years I have been doing this. Acres burned, intensity, all have drastically increased.”

However, armed with the knowledge of how wildfires behave, allied with ever more capable technology, aerial firefighters are well placed to battle this increasing threat.