JACKSON, Wyo. – Following an extensive damage survey, the National Weather Service in Riverton has confirmed that a strong tornado touched down in the Gros Ventre Wilderness east of Jackson at about 9,400 feet on June 12, 2022.
The tornado has been given a high-end EF-2 rating with estimated winds of 128-131 mph. Tornadoes are rated using the Enhanced Fujita scale on a range of 0 to 5, taking into account numerous damage indicators to determine estimated wind speeds.
This tornado occurred on the same day as the Yellowstone flood event. A stationary front had set up across Yellowstone, resulting in heavy rain and extensive cloud cover.
South of the front, a warm and unstable airmass existed over Southern Teton County. Wind shear (changes in wind speed and direction with height) was also significant, resulting in a favorable environment for thunderstorm updrafts to tilt and rotate.
Between 3:00 and 3:30 p.m. on June 12, a storm developed southwest of Swan Valley, Idaho before intensifying and developing into a supercell thunderstorm as it approached the Wyoming border. The storm produced one-inch diameter hail as it moved over Teton Pass and into the West Bank, causing damage to vehicles.
The center of the storm passed just north of the Town of Jackson, but it did produce wind damage in town, knocking over a large tree on North Willow Street.
As the storm moved into the Gros Ventre Mountains east of town, the tornado formed on the northern side of Sheep Mountain (Sleeping Indian) at an elevation of about 9,400 feet.
The tornado moved to the east/northeast and was on the ground for two miles with a width of 0.2 miles before dissipating at about 8,200 feet prior to reaching Gros Ventre Road. Extensive wind and tree damage still occurred after the tornado dissipated around Crystal Creek Campground.
Here are two images of the tornado path at different zoom levels:
There were “hints” in the immediate aftermath of this storm that a tornado may have touched down due to reports from Bridger Teton National Forest Service staff of downed trees in erratic, criss-crossing patterns.
However, the area of widespread tree damage was deemed inaccessible and not viewable by the National Weather Service damage survey team that visited immediately following the event.
Several months after the event, Bridger-Teton National Forest staff recorded photos from a helicopter of a distinct damage path consistent with the track of the storm and shared them with the National Weather Service office in Riverton.
The NWS Riverton office then conducted a more extensive investigation with help from other Great Plains NWS staff along with satellite imagery. The NWS concluded that the tree fall patterns and damage path were consistent with strong tornadic rotation.
Statement from the National Weather Service in Riverton:
“The EF2 designation comes from looking at the softwood damage indicator of the Enhanced Fujita Scale. Pictures show thousands of pine trees snapped at various heights, with hardly any trees remaining upright. There was some evidence of debarking in photos as well. For this reason, wind speeds were estimated to be between 128 and 131 mph, based on the upper bound for softwood trunks snapped and the expected damage for softwood debarked.
Path length and width were determined from polar-orbiting satellite data from the summer months after the event. Notable decreases in vegetation could be seen, with a clearly defined damage path.”
View the Full NWS Tornado Report
An EF-2 rated tornado is considered to be a strong tornado that produces significant damage.
Here is a guide to the EF-scale for tornadoes:
Tornadoes are a rare occurrence in Teton County, but they are not unprecedented. In July 1987, a massive F-4 tornado (the original “F” scale was used prior to the EF-scale being adopted in 2007) touched down in the Teton Wilderness east of Jackson Lake, and to this date remains the strongest tornado ever documented west of the Continental Divide.
Tornadoes at high elevations and in mountainous terrain are less common compared to the Great Plains and Central/Southern U.S., but they can and do occur under the right setups. So don’t be fooled by the old myth that “tornadoes don’t happen in the mountains.”
Alan Smith, Meteorologist
