Teton-Yellowstone Tornado

Today marks the 30th anniversary of the Teton-Yellowstone Tornado, a windstorm that ripped a 24.4-mile path through the Teton Wilderness, over the Continental Divide and into Yellowstone National Park.

The tornado downed a million trees but spared people. Nine campers in the Bridger-Teton National Forest at Enos Lake were among the handful of witnesses. They described a fast-approaching train-like noise, golf-ball-size hail, but no funnel cloud.

Dr. Tetsuya Theodore Fujita, the man who invented the tornado scale that’s named after him and still in use, wrote that the event occurred in “a most unlikely place.” He classified it as an F4 tornado, on his Fujita Scale that tops out at F5. As such, winds blew at between 207 and 260 mph, “an intensity rarely experienced in the Rockies.”

“Small spotty areas affected by F4 winds were characterized by flattened Engelmann spruce trees, 30 to 40 cm [about 1 foot 2 inches] in diameter, spattered by wind-blown topsoil and debarked,” Fujita wrote in Monthly Weather Review.

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The storm touched down at 1:28 p.m. in the wilderness just north of Jackson Hole and the small community of Moran. It took about 26 minutes to ravage its path, which averaged 1.6 miles wide. It crossed the Continental Divide at 10,070 feet before descending to and crossing the Yellowstone River.

Twenty-eight stereo aerial photographs revealed 72 microbursts and four “spinup swirl marks.” It earned tornado status because Fujita discovered “where rotational winds were evidenced by damage analyses.”

Fujita described the tornado’s source as “a mesocyclone that formed at the intersection of a mesohigh boundary and a warm front.” Alas, the wildfires fires of 1988 burned up all the evidence, cutting his research short.

Andy Norman, who works for the Bridger-Teton National Forest as a fuels and prescribed fire specialist, took the photograph above, likely in 1987.