Trip Planning for Southern Gallatin

Chris Hericks, snow ranger on Beaverhead Deerlodge NF, points to the lower of two surface hoar layers. We are finding similar layering throughout our entire forecast area. The top 18" of the snowpack is weak and will quickly become unstable when it snows. Photo: GNFAC

Looking up from the bottom of the avalanche that killed one snowmobiler on Ski Hill. The crown is visible at the top of the hill. The men in the photo are standing near the trees where the victim was buried. Photo: GNFAC

The crown is not visible (it is down and right) but the X marks the approximate spot the rider was found. Photo: GNFAC

The crown was measured 4-11 inches deep and 75 feet wide. Photo: GNFAC

Looking at a weak layer of facets that the avalanche propagated on. Photo: GNFAC

Looking at the crown from below. Photo: GNFAC

A small, skier-triggered avalanche on Mt Blackmore on Sunday (Feb 6) would be unlikely to bury a skier or rider, but could push them into or off obstacles. Photo: E Stutzman

On Sunday, February 6, Gallatin Country Sheriff Search and Rescue and the GNFAC responded to a avalanche in Lionhead. A snowmobiler was killed on a small steep slope when a shallow avalanche carried him into a terrain trap of trees. Photo: GNFAC

This morning while ascending a line on Sawtooth Mountain (Lower Novocain) we triggered an avalanche (ASu-SS-R2-D2-O)  that caught and carried my partner an estimated 180M and partially buried him. His leg and hand were unburied and excavation of the head was done in less than 2 minutes of the incident. The avalanche only involved new snow from the last 48hrs and was triggered on a MF crust/facet combo 30cm down(formed 1/30/22). The avalanche was 30cm at its deepest and 20-30M wide and ran 250M. We were lucky to find both skis and poles a little ways downslope. No injuries were sustained.

We both agree that we were trying to outsmart the instability that was present on steeper S facing terrain and should have turned around much sooner, we were very lucky. There was 30+cm HST in favored areas and the high winds from 1/31/22 formed some sensitive windslabs in specific areas. 

Graph of Snow Water Equivalent (SWE) at SNOTEL sites in the GNFAC forecast area from October 1, 2021 to January 30, 2022. It highlights the extended dry conditions in January that contributed to weak layers forming at the top of the snowpack. GNFAC

Riders reported on 1/15/22: "Some surface hoar is forming on nearly every aspect at all elevations. over 1 cm thick in some areas." Photo: B. Rasmussen

Riders reported on 1/15/22: "Some surface hoar is forming on nearly every aspect at all elevations. over 1 cm thick in some areas." Photo: B. Rasmussen

Settlement rings around the base of trees near Cooke City, January 15, 2022. Photo: B. Fredlund

From email 1/9/22: "Skier triggered cornice failure avalanche. Broke at skis 10-12 feet from the lip. No one caught or injured."

From email 1/9/22: "Skier triggered cornice failure avalanche. Broke at skis 10-12 feet from the lip. No one caught or injured."

A sled was recovered uphill of the 2 avalanche victims in the same area it was stuck. The sled was found with a probe line and is buried 3-4 feet deep. The avalanche crown can be seen in the upper slopes above them. Photo: GNFAC

The crown of the avalanche that killed two snowmobilers on December 27, 2021 was 300 feet wide and 4-5 feet deep. Photo: GNFAC

These are the two sites where the 2 snowmobilers were recovered. They were buried 4-5 feet deep in debris piles that measured 9 feet deep. Photo: GNFAC

Ian Hoyer stands next to the crown where we dug a snowpit and investigated the snow structure. The crown averaged 4-5 feet deep. Near his right knee is the layer of weak faceted snow that broke 40 cm above the ground. Above this layer was a thick slab of windblown snow. Photo: GNFAC

Dave Zinn of the GNFAC gets 3 layers breaking in his Extended Column Test. About 3 feet of snow fell in the last 4 days which got blown into wind slabs. The weight of the new snow is also creating instability on a weak layer of sugary facets near the ground. Photo: GNFAC

A skier in the Southern Madison Range remotely triggered this avalanche in the Bacon Rind area from a flat bench above the slope. It broke over 50-75' away where the slope got steeper. Human-triggered avalanches are likely. Avoid steep terrain until the snowpack stabilizes. Photo: Anonymous 

From obs: 12/12/21: "Heavy wind loading from gusty SW winds and recent snowfall. Made for some touchy conditions. This was at 9100’ between Sage and Sunlight basins." Photo: JR Mooney

New snow was blown into thick drifts that can be triggered by skiers or riders. Cracking like this is a sign that drifts are unstable and could slide on steeper slopes. Photo: GNFAC

From email (12/5/21) : "Small avalanche triggered while approaching ice climb in East fork of Hyalite basin. 

Another D1 natural avalanche was observed later in the day similar aspect/elevation

NE @7600’
SS-AFu-D0.5-I"

Photo: A. Schoening

Skiers on Mount Blackmore observed cracking within the freshly wind-loaded snow on a southeast-facing slope just below the ridge (11/24/21). Photo: J Schack

From e-mail 11/7/21: "...Once in airplane bowl we saw multiple large slides that ran last night, syn-storm. Most of which came down from the East face of Sac. A few 200-300’ wide and running the length of the bowl.,,, attached is a grainy cell phone pic of the slides in Airplane Bowl." -Anonymous.

From email 11/4/21: "...noticed two small wet loose avalanches in the east facing bowl between Pomp and Hardscrabble Peaks." Photo: H. Darby

From e-mail 11/4/21: "Hiking up in the Bridger Range from Sacagawea Pass and noticed no faceting of the current snowpack. The snow near the pass and on the ridge is very wind affected as is to be expected and dropping into the bowl on the east side of the Pass the snowpack there has a distinct sun crust. Dug around a little bit at 8600 ft on a NE aspect and found a sun crust of about two inches with what felt like rounded grains below that. Even in the direct sun, the crust was taking a long time to rewarm and was pretty slippery..." Photo: H. Darby