• A still shot from the Fort McMurray International Airport webcam showing explosive development of the fire near the city on the afternoon of May 4th.
    A still shot from the Fort McMurray International Airport webcam showing explosive development of the fire near the city on the afternoon of May 4th.

Canadians have watched in horror as, for the past two days, a wildfire near Fort McMurray, Alberta has burned out of control, destroying homes and forcing the evacuation of the entire city of 80,000 people.

The disaster has resurrected painful memories of the wildfire that engulfed another northern Alberta community, Slave Lake, almost exactly five years ago, and left many wondering how this fire so rapidly grew beyond the control of suppression crews. But fire behaviour experts who have been monitoring conditions in the province with growing concern say it was only a matter of time before a potentially life-threatening fire broke out.

"It’s kind of a perfect storm of conditions," said Kyle Brittain, a former wildland firefighter who worked on a rappel crew in the province from 2010 to 2014. "The ground is snow-free and very dry, especially at the surface, and we're also in the midst of a phenomenon called the 'spring dip,' when the tree canopy is naturally much drier."

Factor in record-breaking heat and gusty winds, and a spark can quickly become an inferno.

"It’s a combination of factors all coming together at the worst possible time," Brittain said.

The maps below put the fire in context:

Alberta is bone-dry

The Canadian Forest Fire Weather Index (FWI) is a system for determining the fire danger in an area. Daily observations of temperature, relative humidity, wind speed and 24-hour rainfall are taken in order to calculate the relative moisture content of the soil and organic ground cover, which in turn is used to predict how a fire would behave.

Parts of Alberta, particularly in the northwest, have been exceptionally dry for the past 12 months. With drought conditions present even in deep, compact soil, fires are easily ignited.

An unwinnable fight?

The most effective way to suppress a large fire is by dropping water on it from the air; however, during peak burning, which usually occurs in the late afternoon, the heat from the flames is so intense that water can evaporate before it reaches the ground.

Fighting fires is easier at night, when winds are calmer and humidity is higher, but as water bombers cannot fly at night, suppression efforts must be undertaken by personnel on the ground.

Ultimately, a change in the weather is what is needed to bring the Fort McMurray fire under control, but current forecasts show it could be more than a week before the region sees any substantial precipitation.

Infographic: Alissa Dicaire/Alexandra Pope