Trip Planning for Northern 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

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

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

From obs on Divide Peak (2/4/22): "On the way out a surfed over a steep roll over that fractured and slid. It appeared to have slid on the new snow interface." 

From obs (2/4/22) on Divide Peak: "the wind was cooking for most of the day and each lap the skin track was covered in places. There was wind loading along the ridge the snow was pretty cohesive and wanted fracture and propagate but I was not surfing steep enough slopes for this to happen"

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

From Obs 1/23: "While on the ridgeline on the way up we triggered many small wind drifted pockets."

A view of Sacajewea Peak from the Fairy Lake road. Evidence of winds are seen on the right shoulder of the peak. Photo: GNFAC

Slopes on Hardscabble Peak in the northern Bridger Range show bare slopes that got blown clean by wind. Photo: GNFAC

In the northern Bridger Range we dug a pit at 8700 feet on a north facing slope before skiing the chute into the basin. Our stability tests did not break and all evidence pointed to a LOW danger. Photo: GNFAC

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

Looking up at the Fat Maid from Maid of the Mist basin. Strong winds over the last week have scoured the alpine, exposing lots of rock. Photo: GNFAC

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."

It was easy to crack the thin wind slabs that formed from strong wind the last 2 days. They were not propagating, but cracking indicated potential instability on wind drifts. Photo: GNFAC

Strong wind in the previous 2 days sculpted the snow surface into waves of sastrugi. Photo: GNFAC

Wind in the last 2 days gusted 45-70 mph and stripped some starting zones down to dirt in Beehive Basin. Photo: GNFAC

We intentionally triggered this 6-8" deep wind slab on Saddle Peak on December 23, 2021, E aspect at 9,000'. It showed us that recently formed wind slabs were still reactive. This hard slab formed over low density new snow which made it unstable. While not large, these slides will easily push you down and can be harmful if they push you into hazardous obstacles or terrain traps. Photo: GNFAC

Pit from 12/22/21 at 9,850' on the NE face/shoulder of Mt. Blackmore. Snow depth was 111cm, first ECT was ECTN10 below the wind slab then ECTN22 on facets at 70cm. A second test was ECTN17 on that facet layer, then ECTP20 on depth hoar at 35cm. A third ECT was ECTP17 on the facets at 70cm, then a fourth ECT was another ECTP17.... I was moving into shallower snow as I got more unstable results, down to about 90cm HS. These weak layers are not easy to trigger or showing obvious signs of instability, but we will need to be careful when we get more snow, especially during large cumulative loading or big wind events. Photo: GNFAC

North face of Mt. Blackmore on 12/22/21. South-southwest winds were moderate-strong and scouring more than loading it seemed like, but isolated slabs and whales of snow could be found. We did not get any drifts to crack or collapse. Fresh wind slabs were 2-4" thick, 1f-P hard, and not very continuous. Photo: GNFAC

Cornices that formed mid-slope, indicating recent heavy wind-loading in the Bridger Range. Strong southwest wind between 12/18 and 12/19/21 drifted recent snow into hard, pillowy drifts. We avoided these drifts on steep slopes to give them a day or two to stabilize. Photo: GNFAC

These pillowy, hard drifts formed from strong southwest wind overnight between 12/18 and 12/19/21 in the Bridger Range. We saw minimal signs of instability, lke whumphing or cracking in these drifts, but avoided these features on steep slopes until they have more time to gain stability. Photo: GNFAC

From obs 12/18/21: "95cm Snow depth at around 9400’ 40cm of new snow on early December ice crust Ectx18 Will have to see with more loading on early December interface if it becomes reactive All alpine terrain was heavily stripped from the wind."

On 12/16/21 A skier in a group of three triggered and was caught in this avalanche next to The Apron at Bridger Bowl. The ski area is closed and backcountry conditions exist. Nobody was injured.

From e-mail: "We had a group of three skiing up at the Bridger Apron today. We skied a more main slope in the field north of the slope with hidden couloir, snow was very stable and has been getting a lot of tracks. For a second run we skinned up the main slope under hidden and started our run in the trees slightly south of this slope. Not many tracks over there and not a good enough evaluation of the snowpack. We were planning on skiing a northeast facing chute through the trees that had very nice looking snow similar to what we had skiied earlier. I skiied in and had about 3 amazing turns, definitely partially due to the wind loading at this aspect. After three turns my feet were taking out from under me and I got caught in a slide keeping skis perpendicular to slope for 15-20’. This avalanche carried me rapidly and cleared the snow to the rocks below in which I was able to come to a hault and watch the rest of the sluff slide past me. After looking at the conditions after, this windy aspect seemed to have a very faceted layer about 8” down that acted as the crown. No injuries, a lost ski pole in the runout which extended down the slope maybe another 40’. The wind scoop on top and seeing these facets should have been a clear sign prior to skiing. Must be more diligent even in areas of high traffic. When dropping in to ski on first turn or so I remember hearing a possible whumpf."

Skiers up the East Fork of Hyalite Creek observed this small avalanche on a road cut. Photo: S. Reinsel

From IG 12/12/21: @montanamountainmedicine

From obs: 12/12/21: "Shooting cracks and whoomphing in wind loaded areas. An approximately 15x30ft wind slab cracked along the base of a rock band and settled at the base of P2 on high fidelity. Was triggered while traversing along the rock band to gain the second pitch, 1-2 inches of facets on the ground. Wind slab of 6-36in in the gullies." Photo: M. Hearley

In the Bridger Range on December 10, 2021 2-3" of low density new snow was drifted into small soft slabs that were easy to trigger. Photo: GNFAC

This pit was dug in Hyalite Canyon near Twin Falls. It showed 2 mm facets (sugar snow) underlying the snowpack. This layer did not break in stability tests, but anticipate these grains will get weaker with time. Photo: GNFAC

For the Bozeman Ice Fest we investigated the Silken Falls and Avalanche Gulch gulleys. They were wind-loaded and had weak snow mid-pack that was unreactive. Avalanches in these gulleys would be deadly, so be extra vigilant in your assessment before crossing. Photo: GNFAC

For the Bozeman Ice Fest we investigated the Silken Falls and Avalanche Gulch gulleys. They were wind-loaded and had weak snow mid-pack that was unreactive. Avalanches in these gulleys would be deadly, so be extra vigilant in your assessment before crossing. Photo: GNFAC

We found 80 cm (2+ feet) of snow on a NE facing slope at 8,000 feet outside Bridger Bowl's Boundaries. The snow was supportable with a weak layer at the blue card. Faceted, weak, sugary snow is the layer of concern, but it was not that bad...yet. We'll be watching to see if it gets weaker. Photo: GNFAC

Monday night's new snow formed wind slabs from the strong wind on Tuesday. We are finding these throughout southwest Montana. Photo: D. Britt

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

This post and picture was on the FB ice climbers page. This is from Comet Alley, a steep gully off the East Fork Road:

Today we found that this gully has some significant loading. We triggered a few wind slab slides on the approach. We managed to get a quick lap on the route and got out before it got loaded more. TBH with more unconsolidated snow I’d reconsider going there.

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