Weather plays a central role in most wildland fires, and we got a grim reminder of that earlier this week with the Yarnell Hill fire in Arizona that took the lives of 19 firefighters. KPLU weather expert Cliff Mass dug into the meteorological data surrounding that fire and came away disturbed. He says the conditions that caused that fire to blow up and reverse course, right on top of the firefighters, were quite predictable.
"That's what's disturbing. This really was foreseeable. You could see a satellite animation or a radar loop. You could see this line coming toward you. And then, in fact, some of our high-resolution computer models were already that morning showing this kind of thing could happen," he said.
“It was clear meteorologically what happened," he said, adding a line of thunderstorms north of Yarnell Hill was moving south. Then came something called a gustfront, which is often found in front of thunderstorms and cause the winds to pick up speed and sometimes change directions.
"As these thunderstorms moved toward Yarnell Hill, all of a sudden, this gustfront hit. Now, before the gustfront hit, the winds were from the south at around 10 to 20 miles per hour, so the fire was being pushed northward.
"But then, as this gustfront moved through, the winds reversed 180 degrees, and gusted up to 40 to 60 miles per hour. And that caused the fire not only to turn, but to explode—and unfortunately explode right in the vicinity of those firefighters," he said.
Mass says the tragedy shows the need for "better meteorological input, especially on these early fires before a meteorologist is assigned."
The old adage says summer in Seattle starts on July 5, but Mass laid that myth to restlast year. And indeed, this weekend’s forecast sounds more like late June than blazing July.
Weekend forecast: Sunshine, if you're patient
Mass says expect the classic pattern of cloud cover in the mornings, gradually burning off to reveal blue skies by afternoon. High temperatures are expected to creep into the mid-70s through Sunday.
“Well, it’s not going to be perfect … a lot of clouds in the morning, and then breaking up in the afternoon," said Mass. “Fortunately, it’s going to be much better after that.”
Things could warm up more substantially into the middle of next week, and in any case there’s little or no rain expected throughout the region for the foreseeable future. All that dry weather has authorities on high alert for wildfires.
Do you have a weather question? Cliff Mass occasionally answers reader questions on the air. Share yours here (at the bottom of the page, where you can sort the questions by "newest to oldest").
The weekly KPLU feature "Weather with Cliff Mass" airs every Friday at 9 a.m. immediately following BirdNote, and repeats twice on Friday afternoons during All Things Considered. Cliff Mass is a University of Washington Professor of Atmospheric Sciences, a renowned Seattle weather prognosticator, and a popular weather blogger. You can also subscribe to a podcast of “Weather with Cliff Mass”shows.
