2024/01/14 - Wyoming - Little Poudre Mountain, Prater Canyon

Published 2024/02/15 by Staff - Bridger-Teton Avalanche Center

The snowy season started with early snow in October, followed by two drought periods. The first in November lasted 11 days. The second and more prominent one in December lasted 23 days, with only a small break for three days of light snow around Christmas. The December drought was accompanied by very cold temperatures and many days and nights of clear skies across the region. The time and weather conditions were conducive to extensive near-surface faceting and surface hoar growth, forming a 6+ inch thick layer of weak snow (Figures 3, 4 and 5). Winds remained light throughout this time, leaving many areas of surface hoar and facets intact, and it was noted in alpine areas up to 9,000 feet and higher. The following is an excerpt of the weekly Snowpack Summary issued 3 days prior to the avalanche:

On January 4th, we buried a weak layer that will remain active for the foreseeable future. January 4th-5th initiated the first round of light precipitation we received in weeks. Northwesterly flow favored the west Tetons and areas of the Salt portion of the Greys (forecast zone), depositing upwards of 7+ inches in these areas… On January 7th-8th, light snowfall continued, with the west side of the Tetons picking up an additional 6", the east side an additional 1-2", and the northern portion of the Greys an additional 2-3"... Throughout these storms, winds remained light and northwesterly.  Due to the calm nature of these storms, many layers of weak snow that generally get disturbed with an incoming storm (surface hoar) were preserved, even at upper elevations across every forecast zone.

January 4th initiated the burial of the December drought snow with northerly flow and light-density snow accompanied by very light winds. This mild storm buried weak snow just enough to be preserved from strong winds from subsequent incoming storm systems. On January 9th, a strong Pacific weather system brought increasing southwest winds with gusts in the 30-40 mph range. Intense periods of snowfall on the 9th and 10th brought 11 inches of new snow containing 0.9” of water to nearby Willow Snotel. Northwest flow on the 11-13th brought another 6” of new light density snow containing another 0.5” of water. The December drought layer of weak snow was covered by light-density snow and light winds. Subsequent snowfall added up to 32” total on the weak layer since January 4th. (Fig 6)

Public messaging on the storm system’s impacts was widespread. A winter storm warning was issued on the 9th and continued through the 11th. An avalanche watch was issued by BTAC on the 11th and upgraded to an avalanche warning on the 12th. This warning continued through the day of the accident and was finally canceled on the 15th. 

The forecast on the day of the incident described the persistent slab avalanche problem as follows:

Large, deadly avalanches failing on very weak snow formed in December are a real threat today. In the mid and upper elevations, avalanches will break 3 to 5 feet deep. Below 7,500’ slab depths will be in the 1 to 3 foot range. All aspects (shaded and sunny) at all elevations are suspect. Only the lowest elevation slopes that were bare ground prior to January 4th have escaped this problem. Slabs could be triggered from a distance, or wait until you have committed to the slope to release. Approximately 10 inches of new snow fell overnight in the upper elevations of the Salt River Range. This additional load will push an already weak snowpack over the edge. Extremely careful route finding is of the utmost importance today. Keeping slope angles below 30° and staying well away from terrain that is connected to avalanche paths is critical. This also means being aware of the terrain above you as remote triggering is possible. Groomed trails that cross avalanche paths should be evaluated carefully and crossed one at a time, if at all.

From January 4th to the 13th, 57 avalanches D2 in size or greater were reported in the Greys and Tetons forecast zones, most of which failed on this layer. As visibility improved on the 14th and 15th, another 30 avalanche observations were submitted.

These skiers were residents of Star Valley Ranch and lived within a few miles of the canyon. The pair approached via snowmobile to shorten the approach to the usual skin track which starts a mile from the end of the plowed road. They ascended a steep skin track on a wooded slope thought to be relatively free of avalanche hazards, although it crossed through several avalanche paths (Fig 7). The pair gained the ridge, noting one collapse in the snowpack along the way, and headed east to the top of a sub-ridge of Little Poudre Mountain. The ridge is exposed to wind, and the pair found stiff, wind-hammered snow from moderate to strong winds two days prior which was now capped with soft snow. The pair made a quick plan to ski for a few hundred feet and regroup below a patch of trees to plan the next pitch of skiing. (Fig 8) Skier 1 told Skier 2 to follow his tracks, stay on the ridge, and then began skiing. Seconds later, Skier 2 followed. Skier 1 skied fast, his normal style, but soon noticed avalanche debris flowing in the gully to his left. He stopped on a high point on the ridge and planned to descend towards the debris pile first along the main ridge to avoid the bushes and trees in the gully and potential hang-fire above (Fig 9 and 10). He descended to where debris began to accumulate and initiated a beacon search. He acquired a signal 1.2m beneath the surface and quickly dug to expose his friend lying face up, head downhill. Skier 1 noted no signs of impact to his friend's helmet but later noted an angulated leg fracture. He also noted no ice mask or snow in the mouth. He found no carotid pulse or signs of breathing and began CPR, which he continued for one and a half hours. An autopsy would later rule that the cause of death was asphyxia.

All of the fatal avalanche accidents we investigate are tragic events. We do our best to describe each accident to help the people involved, and the community as a whole to better understand them. We offer the following comments in the hope that they will help people better understand and avoid future avalanche accidents.

Skier 1 had lived and skied on a regular basis in the area for 25 years. He had been skiing regularly with Skier 2 for over five years and was a mentor. Skier 1 shared that the adjacent and more obvious gully features avalanched more regularly and that he thought that the rib feature was generally a safe route that he had never seen slide. In this case, the chosen route down the rib did not avalanche, but skiing 30-40’ left put Skier 2 into steeper terrain or perhaps over a thin spot in the slab. Considering terrain maps and photos, it’s clear that the route, and most of the surrounding terrain, is between 35 and 40 degrees even on the rib they intended to ski. (Fig 11).

Skiing at the same time during periods of instability reduces one’s safety margin considerably, particularly in steep terrain and in high-hazard areas. Terrain choices like the crest of the rib are perhaps lower risk than the steeper terrain nearby, but 35 and 40 degree slope angles significantly narrow the safety margin, particularly when skiing at the same time during elevated avalanche danger. 

Another misconception that was at play in the incident was the assumption that a recent avalanche had occurred and made the slope safer. Some portions of the face had avalanched, but during the previous avalanche cycle. Persistent weak layers can easily avalanche again since the snow crystals that make up the weak layer often remain undisturbed after the initial avalanche, only to be reloaded by new snow, which may avalanche again. It is unclear what parts of the area had avalanched, though a flank wall is visible beneath the storm snow (Fig 12)

The skier’s familiarity with the terrain may have also contributed to this incident. In Backcountry Skier’s Guide: South, author Tom Turiano describes this run as “a popular gem of the Salt Rivers, this 1,500’ face features three main ribs divided by gullies that culminate in extremely dangerous starting zones” and “the safest routes down follow the ribs or the tree line on skier’s left.” This run was a “go-to” descent in the pair’s backyard. They had skied here on days with elevated avalanche hazard for many years. It’s possible that they had an elevated level of acceptable risk on this line during a period of high instability with an unusual weak layer in the snowpack. We are all vulnerable to the normalization of deviance in risk acceptance, but hopefully, learning from others can help guard against this potential error. 

BTAC staff are grateful for the information shared by the party involved. Sharing experiences like this openly is difficult but critical to creating an opportunity for the community to better understand and learn from these tragedies. Our sincere condolences to family, friends, and others impacted by this loss of life.

We are grateful for the efforts of Star Valley Search and Rescue and Teton County Search and Rescue to perform this mission in dangerous conditions and the county Sheriff's offices in Teton and Lincoln County for allowing BTAC personnel on the scene to begin the research needed to produce this report.

BTAC Report