Unpredictable winds make wildfires an erratic adversary: experts

Hot weather and dry conditions are the usual suspects in any wildfire season, but a complex interplay of topography and unpredictable winds can create particularly challenging adversaries for firefighters, experts say.

In British Columbia, shifting wind patterns have been a key concern for crews battling a fire in the south Okanagan that has forced the evacuation of hundreds of homes.

Mary-Ann Jenkins, professor emeritus of atmospheric science at York University in Toronto, said fire generally moves in the same direction the wind is blowing.

But mountains can complicate matters, she said.

The Rockies, for instance, influence a range of factors, including humidity and localized wind directions.

"Because of the Rockies, wind can be channelled through valleys. It changes — the wind over ridges in the mountains and also sometimes you have very severe downslope winds,'' she said.

"And another thing that people don't know is that winds going up a hill tend to accelerate. As they go uphill, they get stronger and stronger before they reach the top.''

Jenkins said the Rockies create a unique phenomenon called Chinook winds, which are extremely drying, can be experienced year round and can add to firefighting woes.

"The weather conditions at the local level in a mountainous region are difficult to forecast. Because there are so many things that can happen due to topography.''

Such unpredictability has been felt acutely around Keremeos, in British Columbia's south Okanagan. The area's Indigenous name is "valley of the three winds,'' said Tim Roberts, the elected regional director.

On Monday, B.C. Wildfire Service information officer Bryan Zandberg said winds around the Keremeos Creek fire were light, at about 15 kilometres per hour, which allowed firefighters to make good progress building containment lines.

But the winds still had the potential to push flames south toward the villages of Keremeos and Olalla, as happened last week, he said.

"We're making really good gains,'' he said, but added "if the wind picks up, you know, the wind could take it where it wants to.''

More than 500 homes in the area have been ordered evacuated since the wildfire was reported on July 29.