The warning foreshadows worsening weather conditions — high winds throughout the Okanogan Valley will make things even more difficult for firefighters.
Firefighters in the North Cascades face some of the most difficult conditions nature can dish out Friday — gusts of up to 50 mph that can create the kind of firestorm that “just nukes everything in its path,” said Weather Service fire-weather forecaster Andy Haner.
“This is going to be a critical weather situation,” Haner said as a “red flag warning” was issued for many mountain areas.
The warning, in effect through Friday night, says “a combination of strong winds, low relative humidity and warm temperatures will create extreme fire-growth potential.”
Forecast for Omak, Okanogan County
Wind: Gusts up to 46 mph
Wind: 6-10 mph
Wind: 9 mph
Source: National Weather Service, weather.com
Winds feed a fire oxygen, helping it grow. The process often peaks in the late afternoon when winds and temperatures are at their highest.
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But experts note it’s not just the winds blowing into area that can spread a fire. Large fires can generate their own winds, propelling flames rapidly across valleys and up slopes.
Climate scientist Terry Clark, formerly with the National Center for Atmospheric Research, said fires with sufficient oxygen and fuel can create powerful “fire whirls” capable of hurling flaming logs and other burning debris onto the surrounding terrain.
On the “How Stuff Works” website, Clark said a moving fire can generate wind up to 10 times as great as the ambient wind.
Wind-driven fires spreading through treetops can shoot out blasts of flame reaching 300 feet in front of the main body of the fire and traveling at 100 mph, Clark said.
In the Okanogan Valley, where a fast-moving fire killed three firefighters near Twisp on Wednesday, sustained winds of 25 mph to 30 mph and gusts approaching 50 mph are forecast Friday.
“All of Eastern Washington is going to be windy, but the Okanogan Valley is expected to have the strongest winds,” Haner said.
When winds are calm and a fire moves through low vegetation, fire crews can attempt to clear fuels out of its path. But Haner said high winds spread fire through the crowns of trees, allowing flames to pick up speed as they race up ridges or down valleys.
Summing up the situation, Haner passed along the assessment he heard Thursday from one of his Weather Service counterparts in Eastern Washington: “To say it’s going to be a mess is an understatement.”