JACKSON — While the rest of the country was buried in ice, Wyoming’s northwest corner was trying to get itself out of the snow. The Wyoming Department of Transportation’s avalanche maintenance teams were extremely busy this past month.
The first week of February brought a wet and warm sub-tropical southwestern flow that camped out over Western Wyoming. While the rest of the country was preparing for historic severe weather, so was the maintenance team in the Jackson area.
“This weather pattern is commonly referred to as the ‘Pineapple Express,’ where the jet stream tracks from Hawaii to the western United States, bringing warm and wet air from the tropics,” WYDOT Avalanche technician Jamie Yount said.
With the new load of moisture, several avalanches were observed in both the Hoback Canyon and the Snake River Canyon.
The morning of Feb. 8, a small slide released naturally from the Cow of the Woods path in Hoback Canyon at approximately 5:20 a.m. The slide deposited 4-5ft of debris on the roadway and blocked both lanes of travel.
“Visibility was very poor on all area roads and a vehicle drove into the debris pile and became stuck,” Yount recalled.
A plow was dispatched from the Jackson shop and cleanup began after the stuck vehicle was pulled from the debris. Cleanup was completed quickly with the highway reopened to traffic at 7:09 a.m. However, it was just the beginning of an extensive avalanche event.
Over the two days, the Snake River Canyon experienced a significant avalanche cycle. A total of 15 avalanches impacted the highway through the Snake River Canyon with approximately 30-40 avalanche crowns observed in the greater canyon area.
An avalanche crown is the top fracture surface of a slab avalanche; it’s usually clean cut and smooth-looking snowpack layer.
The morning of Feb. 8, Yount and his team also issued a notification that avalanche control work would be taking place at 9 p.m. over Teton Pass. That evening, maintenance crews immediately began work on detonating avalanche control devices on the pass, bringing down a soft slab that deposited 5-6 feet of debris on the WYO 22. Due to increasing avalanche hazards and significant snow drifting narrowing the road, Teton Pass remained closed for the night.
During the night, however, a vehicle had driven around the west side road closed gate.
“After the vehicle reached the slide at the Glory Bowl, they turned around only to discover that a natural avalanche had occurred at milepost 13.5 and blocked the road with 10 feet of debris. The vehicle was trapped and waited at the summit parking lot until the road was cleared in the morning,” Yount said.
Cleanup operations continued with the highway reopening at 10 a.m. on February 9.
Mother nature was not quite finished yet. The following week, on Feb. 13. in anticipation of a considerable avalanche forecast, Yount and his team planned a second closure of WYO 22 Teton Pass for more avalanche control work. In the early hours of the morning, avalanche crews successfully reduced some of the avalanche risk, but also began preparing for another storm.
As nature dumped more moisture on the Teton Valley, Hoback and Snake River Canyons, several wet slide avalanches were observed around the Jackson area, as the rain weakened the fragile snowpack to the point of failure.
“The snowpack in the Hoback Canyon was the weakest with faceted snow near the ground that has been heavily stressed by the extreme load of new snow,” Yount said.
With natural avalanche activity observed and more snow forecast for the area, a helicopter bombing mission was planned for the Hoback during the next flyable weather window forecast for Saturday morning, Feb. 15.
Partial clearing of the weather on Saturday morning allowed the use of the Teton County Search and Rescue helicopter. The helicopter landed at the Stinking Springs turnout at 11:15 a.m. and preparations were made for the bombing mission. The highway was closed at 11:40 a.m. from Stinking Springs to Granite Creek. Control work began at the Cow of the Woods. The charge triggered a very large avalanche with a 3 foot crown that deposited more than 35 feet of debris in the highway.
Several more charges were detonated throughout the canyon and the helicopter returned to the Stinking Springs turnout with cleanup operations beginning at approximately noon. The road was reopened around 3:23 p.m.
“The debris pile at the Cow of the Woods was impressive with 75 feet of road covered with a max height of 35ft; one of the largest slides to release at the Cow of the Woods path in the last 12 years,” Yount said.
The weather continued to deteriorate and by Feb. 16, two major avalanches in the Hoback Canyon had pushed the boundaries of historically recorded avalanche cycles.
The first, near milepost 151.1 on US 191, released 4-5 feet of debris over 50 feet of highway around 3:42 p.m. The debris was cleared and the road was reopened around 5:18 p.m.
“While several past events have deposited snow in the turnout adjacent to the road, this path has no history of depositing debris into the highway since the road was realigned in the 1960s,” Yount commented.
The second, a large and destructive natural avalanche, released at the Bull of the Woods slide path at milepost 156.5. The slide was a massive class 5 avalanche with the dust cloud depositing 6 inches of snow in the road and multiple 100-year-old trees destroyed by the associated air blast.
“This avalanche buried the old highway (30-40 feet higher than the new road) in the large winter of 1949. When the highway was realigned in the 1960’s, the engineers created a series of mounds in the Bull of the Woods track to disrupt the flow of avalanche debris. The mounds absorbed the majority of the debris and saved the highway from being impacted by this massive avalanche. I would estimate the air blast to be close to a 150 mile per hour gust,” Yount said.
The storm was also creating challenging conditions on Teton Pass. Heavy snow and very strong winds forced a closure of Teton Pass due to winter driving and whiteout conditions. The gates were lowered at 6 p.m. and the remaining traffic was cleared from the highway. Since the road was already closed and clear of traffic and backcountry users, an avalanche control mission was quickly conducted. Visibility improved enough to reopen the road at about 7:30 p.m.
Conditions were also prime for an avalanche cycle on the slide paths near Jackson. A wet slab avalanche was observed at the Welcome to Jackson Hole path just north of the town line. The slide was small and only deposited debris onto the road shoulder.
“The snow supporting structures recently constructed certainly prevented an avalanche from releasing at the 151 path. The location and design of the structures is mitigating the hazard well, considering the large amount of snow and wind this month,” Yount said.
Overall, crews were able to keep up with the excessive snow and wind over the storm cycles to keep motorists safe on Wyoming’s roads.
“I am confident in what our avalanche technician and maintenance crews do in Jackson. They do everything they can to protect motorists in extensive winter conditions,” District Maintenance Engineer Tory Thomas said.
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