24-25

Noticed a large cornice triggered avalanche on Mineral Mtn today. Likely broke on 2/12 or early am 2/13. E aspect ran almost to the valley floor.  Photo: BPG

Noticed a large cornice triggered avalanche on Mineral Mtn today. Likely broke on 2/12 or early am 2/13. E aspect ran almost to the valley floor.  Active Loading today with Strong Gusts from N-S. There were some other small cornice avalanches to the north of this slide that did not trigger larger avalanches.

Lots of snow transport above treeline today south of Cooke City. Wind gusts were strong. 

Triggered a small wind slab avalanche on the east face of mt Blackmore today at 9850 ft elevation. Around 5 inches thick, ~ 20 ft wide, and ran for 100 ft. Photo: I Masi

Triggered a small wind slab avalanche on the east face of mt Blackmore today at 9850 ft elevation. Around 5 inches thick, ~ 20 ft wide, and ran for 100 ft. Photo: I Masi

We rode into the Taylor Fork, down into the bottom of Sunlight Basin, across Carrot Basin and to the Wilderness Boundary. We saw four persistent slab avalanches that likely broke last weekend or at the beginning of the week. All appeared to be snowmobiler-triggered R1-2, D1.5-2 avalanches at broke of the January layer of near-surface facets and surface hoar. Additionally, we saw one wind slab avalanche (R1, D1) in Sunlight Basin. This slide was fresh from this morning or yesterday. 

We dug a crown profile for the persistent slab avalanche in Sunlight (attached). ECTN24 on the SH layer buried 50 cm (20") deep.

We also dug above Carrot Basin on a northeast-facing slope: ECTP14 & ECTN15 on the NSF layer 50 cm deep. 

Near the Wilderness Boundary on a southeast-facing slope: ECTX

Persistent slab avalanches still seem possible, but it they have reached an equilibrium on most slopes that feels like the bottom end of MODERATE danger. Wind slab avalanches are certainly possible with the fresh slide as evidence as well are shooting crack in a drift as we rode in. Outside of large terrain, these will not be that large. 

New snow and increasing wind starting tonight will change the equation. The snowpack can take 0.5" of SWE without notching up the danger, but 0.75" with more coming would make human-triggered avalanches likely. 

Climbed in the Mummy II area in Hyalite today. West facing ~7,500'. Lots of spindrift coming down onto the climbs in the area and we noticed lots of snow blowing around up high. No snow fell while we were there but our trail in was almost fully filled in and covered with a few inches to a couple feet of wind slab on the way out. Saw a small natural slide that started at the bottom of Cyptorchid. Crown was 10' wide and 8-18" deep, it ran 150' down a very shallow slope and covered the climbers trail. 

Triggered a small wind slab avalanche on the east face of mt Blackmore today at 9850 ft elevation. Around 5 inches thick, ~ 20 ft wide, and ran for 100 ft. No skiers were caught but the slab was very reactive. We were assessing the snow as we climbed but skied a slightly more eastern aspect than we were planning and it was more reactive than expected. Strong winds gusting all day, no active transport observed but obvious that the wind slabs have not settled.