ARCHIVED Backcountry Avalanche Forecast
Greys River

Avalanche Warning
ISSUED Thursday, January 11, 2024 - 5:50PM 
EXPIRES Sunday, January 14, 2024 - 10:00PM

Issued Sunday, January 14, 2024 - 6:59AM
Expires Monday, January 15, 2024 - 12:00AM

Author: Noah McCorkel

THE BOTTOM LINE

Very dangerous avalanche conditions exist today. Triggering an avalanche large enough to bury, injure, or kill a person is likely in avalanche terrain at all elevations. In addition, destructive natural avalanches are likely in the middle and upper elevations. Traveling in, near, or under avalanche terrain is not recommended today.

Avalanche Danger
(The incident this is archived for was on the 14th and this advisory is posted as being on the 14th. However, the danger was only rated for the 15th and 16th. The 16th is deleted since the incident was on the 14th, but the 14th was missing to begin with. We assume the rating for the 14th was similar to that on the 15th. - Avalanche-Center.org)

Monday, January 15, 2024
10,500'- 9,000' 4 - High
9,000'-7,500' 4 - High
7,500'- 6,000' 3 - Considerable

Avalanche Problems (2)

Problem #1: Persistent Slab
Problem Type: Persistent Slab
Aspect/Elevation: All except SE-SW 6000-7500'
Likelihood: Very Likely
Size: Large (D2) - Very Large (D3)

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.

Problem #2: Deep Persistent Slab
Problem Type: Deep Persistent Slab
Aspect/Elevation: W-N-E above 7500', SW-SE above 9000'
Likelihood: Possible
Size: Large (D2) - Very Large (D3)

Weak snow formed during a dry period in November persists at the base of the snowpack. This layer is now buried about 5 to 6 feet deep in the Salt River, Snake River, and western portions of the Wyoming Range. It is at its weakest on the north half of the compass. The recent loading events have pushed this deep weak layer to its breaking point in some locations. Deep slab events were observed in the Snake River Canyon yesterday. These very large avalanches are most likely to occur when an avalanche triggered in the most recent snow steps down to weak November snow. Any avalanche involving the entire snowpack will be destructive and likely unsurvivable. 

Areas in the eastern Wyoming Range, Hoback Canyon, and Gros Ventre Mountains lacked significant snowfall prior to the storm cycle beginning January 4th. In these locations, the new snow has fallen on a snowpack that was primarily made up of weak, sugary snow. Deep slab events are not likely in these locations due to the shallower snowpack.

Forecast Discussion

There are no two ways about it. Avalanche conditions are very dangerous right now. A historically weak snowpack has been overloaded by nearly 5 feet of snow containing 4.5 inches of snow water equivalent (SWE). Widespread natural avalanche activity, some of which produced very large and destructive (D3) avalanches, occurred just two days ago. Continued loading today along with a 20° increase in temperatures over the past 24 hours will make natural avalanches likely again. The widespread and well developed nature of the December weak layer means that avalanches have the potential to propagate long distances, and break well into adjacent low angle terrain. Expect these avalanches to behave differently than what you have seen in the past. It is also important to note that low elevation slopes which previously held little snow are now producing avalanches. Today is a day to step back, let the snowpack adjust, and make very conservative terrain choices.