Jackson Hole, Wyoming is well known for its winter storms and abundant powder. Tornadoes? Not so much.

However, on June 12, 2022, a rare high-elevation tornado occurred in the Gros Ventre Mountains just east of Jackson Hole between about 8,210 and 9,370 feet. It was not a small tornado either, with maximum winds of 128-131 mph, resulting in a high-end EF-2 rating.

The remote nature and inaccessibility of this terrain made it difficult and more time-consuming than usual to complete a damage survey in the aftermath of this event. However, the National Weather Service office in Riverton conducted a thorough and extensive investigation, eventually determining the EF-2 tornado rating in April 2023.

The storm produced severe weather as it tracked over Teton Pass and just north of Jackson, resulting in a dramatic scene as a rotating wall cloud could be seen from Highway 22 between Wilson and Jackson. The tornado eventually formed once the storm was about 13 miles northeast of Jackson in the Gros Ventre Wilderness. 

Supercell thunderstorm with rotating wall cloud near Teton Village as seen from Highway 22.

Storm Environment

The storm formed in a favorable environment, as cloud cover from earlier in the day had given way to sunny mid-afternoon conditions across Southern Teton County and points south, allowing solar radiation to heat up and destabilize the lower levels of the atmosphere. 

Moisture levels were already much higher than usual across the area, with dewpoint temperatures of around 50 degrees.

The low density warm, moist air near the surface was able to rise rapidly into much colder air aloft, helped by a wind convergence zone (winds blowing from opposing directions that force pockets of warm, moist air upward) that was in place south of Jackson.

Wind shear was also significant, meaning that winds increased rapidly with altitude along with changing wind direction with altitude. This helped to tilt the thunderstorm's updraft, allowing it to strengthen and sustain itself for longer since it was displaced from the rain-cooled downdraft which can weaken a thunderstorm more quickly.

The wind direction also veered with increasing altitude (wind direction shifting from southeast to south to southwest with height), supporting an environment conducive to rotating thunderstorms.

Storm Recap and Setup

The storm initially formed over the Caribou Mountains southwest of Swan Valley in Idaho between 3:00 and 3:30 p.m., before intensifying into a supercell thunderstorm as it approached the Wyoming border around 4:00 p.m., prompting the National Weather Service in Riverton to issue a Severe Thunderstorm Warning for Teton County.

The storm was fast-moving and took an east/northeast track at about 55 mph, moving across Teton Pass at 4:10 p.m. and Moose and Kelly around 4:30 p.m.

Large hail estimated to be at least one inch in diameter was reported over Teton Pass and in Teton Village as the storm moved through, which dented the hood of a vehicle as it drove over the pass per a National Weather Service report. 

Wind damage also occurred with this storm, including a large pine tree that fell over Willow Street in downtown Jackson and reportedly just barely missed hitting a vehicle that was driving by. 

As the storm approached Teton Pass, it began to take on the shape of a "hook" on radar as it approached Teton Pass, which indicated that the thunderstorm's updraft was rotating. Veering wind directions with altitude, possibly aided by local terrain influences on winds, contributed to the rotation. 

The storm's rotation was also evident visually, and a wall cloud even formed beneath the base of the storm, indicating the lower portion of a strong updraft. 

Another view of the rotating supercell thunderstorm from Highway 22 between Wilson and Jackson

Tornado Summary and Damage Survey

Once the storm moved east of Jackson Hole, it headed into the more remote Gros Ventre Wilderness where it ended up producing a tornado. Initially, widespread wind damage was reported near the Crystal Creek Campground just off of Gros Ventre Road southeast of Slide Lake.

In the days to follow, there were hints 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. Initial damage surveys by the National Weather Service were unsuccessful due to the difficulty of the terrain.

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.

Aerial view of the tornado damage path. Photo: USDA Forest Service // Teton Interagency Helitack // NWS Riverton 

After consulting with other Great Plains National Weather Service offices, studying the tree damage patterns, and matching up the path to where there was radar-indicated rotation, the Riverton office was able to determine a tornado had occurred.

Further investigation of the tree damage – which included thousands of uprooted trees, some of which had been debarked – led to wind speed estimates of 128-131 mph. This is considered a high-end EF-2 rating on a 0 to 5 scale. EF-2 tornadoes are considered to be "strong" tornadoes. 

The Enhanced Fujita (EF) Scale for rating tornadoes based on estimated winds and related damage

Based on the damage path, the tornado was on the ground for 2.13 miles with an average width of 360 yards, or 0.2 miles. The tornado touched down at approximately 9,370 feet on the northern side of Sheep Mountain before lifting at around 8,210 feet after traveling in an east/northeast direction. 

Approximate tornado damage path

Thankfully, the tornado occurred in rural terrain well away from any roads, trails, or campgrounds and no injuries or structural damage occurred as a result. The tornado was also not witnessed by anyone, being in such a remote area.

After the tornado lifted, it still produced severe straight-line wind damage around Crystal Creek Campground, but there were no injuries. 

NWS Riverton Tornado Recap and Damage Report

Historical Significance

Tornadoes are rare in Teton County and Northwest Wyoming, but they are not unprecedented. In fact, a much stronger tornado once occurred in Teton County about 35 years prior to this event. On July 21, 1987, a violent F-4 tornado (on the original Fujita scale) tore through the Teton Wilderness east of Grand Teton National Park.

This tornado was on the ground for 24 miles and was 1.5 miles wide at times with estimated winds of over 200 mph. It also crossed terrain over 10,000 feet. 

To this day, the 1987 Teton County tornado is the strongest on record west of the Continental Divide, the strongest on record in the State of Wyoming, and the highest-elevation violent tornado (F/EF 4 or 5 rating) on record.

Tornadoes are relatively rare in the mountains west of the Continental Divide, due to a lack of warm and moist air originating from the Gulf of Mexico compared to areas east of the Continental Divide.

However, mountain tornadoes west of the Divide can and do happen when conditions are just right. Last year, another EF-2 tornado touched down in the foothills of the Uinta Mountains in Northeast Utah.

While mountain tornadoes are less common overall, there has been evidence in recent scientific studies that in some instances when conditions are otherwise favorable, changes in terrain over short distances can actually enhance the process of tornado development.