How freakish weather just came alive in the West

“It’s extreme weather.”

BY MARK KAUFMAN

Over Labor Day weekend, the National Weather Service posted footage of a parade of tumbleweed’s vigorously blowing through Idaho.

In much of the Western U.S., the weather has been extreme and fiery over the last few days. A major culprit is a massive zone of cold air that swept down from Canada and clashed with a zone of warm, high pressure parked over the West.

“When you bring those two systems together — anomalously strong for this time of year — the atmosphere goes into freakout mode,” said Dave Lawrence, a meteorologist with the National Weather Service.

The meeting of these two potent and contrasting weather systems throws the atmosphere out of whack and churns up winds, particularly as winds rush downslope and intensify. Powerful gusts stoked severe dust storms in Washington — so blinding they forced highway closures. The dry winds fanned giant, rapidly moving wildfires in parched regions of the Pacific Northwest, one of which decimated 80 percent of the buildings in the eastern Washington town of Malden. In Utah, dangerous winds toppled semi-trucks and ripped big trees from the ground. “It’s extreme weather,” said Lawrence.

But it’s not wind alone that’s impacted the West. Another extreme, record-breaking heat wave cooked areas of Southern and Central California over Labor Day weekend, the result of a robust high pressure system over the region (zones of high air pressure typically bring sunny, warmer, and dry weather to an area while keeping moisture away). These heat waves, amplified by a relentlessly warming climate, dry out vegetation and set the stage for rapidly burning, enormous fires. That’s exactly what’s happened over the last month during the Golden State’s record-breaking fire year. It continues to happen: On Tuesday morning, the California National Guard used helicopters to rescue people trapped by violent flames in the parched Sierra Nevada. Robust winds, rushing down mountain slopes, have only amplified blazes.

Meanwhile, the cold air pouring down from Canada brought plunging temperatures to Colorado. Denver hit 101 F on Saturday, its highest ever September temperature. Temperatures reached into the high 90s on Monday, but then flipped to snowstorms on Tuesday.

“There are records being broken all over the place,” said Jeff Weber, a research meteorologist at the University Corporation for Atmospheric Research. “It’s an amazing, energetic, record-breaking system we have in place.”

The recent spate of winds out West comes at a terrible time. Much of California and areas of Washington and Oregon have been parched by persistently hot and dry weather conditions, including a lengthy record-breaking August heat wave in California.

“Each heat wave dries out the vegetation more,” said Daniel Swain, a climate scientist at UCLA and the National Center for Atmospheric Research.

Now, in September, there’s heat, more wind, and a drier atmosphere. “Vegetation is at record dryness in many places,” said Swain. “It makes wildfire severity much worse.”

“It’s extreme weather.”

Critically, California has been warming since the late 1800s, which means vegetation has grown drier in a region that already experiences arid summer and fall conditions. Higher overall temperatures mean more blazes. Between 1972 and 2018, the amount of land burned in California grew fivefold, largely due to increased summertime burning in forests. Seventeen of the 20 largest fires in state history have burned since 2000.

“We’re seeing the consequences of a background state that is more conducive to these extreme fires,” explained Swain.

On Tuesday evening, wildfires raged in California, Oregon, and Washington. The National Weather Service warns of “extreme” and “critical” fire danger in these regions.

The fire season in California, already one of the worst on record, will almost certainly get worse. The fall brings dreaded offshore winds, which stoke big blazes in both Northern and Southern California. Down south, the hot, dry winds are called “Santa Anas.” These winds originate in the interior Great Basin desert, as cooler air flows downhill, through mountains, drying out and warming up. Weber, of the University Corporation for Atmospheric Research, says this problematic weather pattern may soon take shape in the coming days.

“It’s another ingredient to throw into the apocalypse of 2020,” he said. “Santa Anas are extremely hazardous for fire weather.”

This is especially the case in 2020. The Southwest has been mired in a persistent drought for some two decades — on par with the worst megadroughts of the last 1,200 years. This means ever-drier vegetation, amplified by a warming climate, is then hit with extreme, windy weather conditions. When the winds blow, they feel different than they did two decades ago, before the drought.

“We’re in this very dry period,” said Weber. “The Santa Anas have a much more ominous feel to them.”

Originally published at https://mashable.com