GNFAC Avalanche Forecast for Wed Dec 7, 2022

In the last week, the southern ranges received 2-3 feet of snow. Winds blowing 20-30 mph are transporting recent snow into thicker slabs where human-triggered avalanches are likely (weather log). Persistent weak layers now buried several feet deep complicate the matter in many areas. Active wind-loading will slow with today’s calming winds, but the consequences of triggering a slide will remain high even as the likelihood begins to decrease.

In the mountains near West Yellowstone and Cooke City, a large natural avalanche cycle last weekend following peak storm intensity tipped the snowpack’s hand with avalanches breaking up to 6 feet deep (Alex’s Cooke City Video, avalanche log). Yesterday, I was teaching in the Lionhead area, and participants found a prominent weak layer and unstable conditions near "Ski Hill” (photo). I discussed this weak layer at Lionhead Ridge in my video last week, but with the recent snow, the slab is much thicker. 

Yesterday, skiers experienced the snowpack collapsing under their weight at lower elevations just north of Cooke City (observation). Earlier in the week in the Southern Madison Range, skiers near Bacon Rind triggered “whumphs,” and riders near Skyline Ridge in the Taylor Fork noted a weak, faceted snowpack at lower elevations (observation). On Friday in the Taylor Fork, avalanches failing in wind-drifts was my primary concern, but I suggested digging down to look for weak layers before considering steep terrain (video).

Avoid steep wind-loaded slopes where the avalanche danger is CONSIDERABLE. The danger is MODERATE on non-wind-loaded slopes.

In the mountains around Big Sky and Bozeman, strong winds from the west to the southwest are drifting recent snow into slabs where it is possible to trigger dangerous avalanches. Today, the rate of drifting is slowing. As such, wind-loaded slopes may not show signs of instability before avalanching. Look for indicators of ongoing or recent wind loading, such as the stiffening of the snow surface and shooting cracks to identify areas of concern.

Two days ago, a pair of skiers were caught and carried nearly 600 vertical feet in an avalanche that broke 6” deep on Ross Peak in the Bridger Range. One had snow packed into their mouth and under their eyelids when they came to rest on top of the snow (details and photos). In the Northern Gallatin Range, a skier intentionally triggered a test slope that failed 12-18” deep near Lick Creek (photo). At Divide Peak on Monday, I outlined my concerns about wind-loading on slopes and in gullies in my video.

Human-triggered avalanches are possible, and the danger is rated MODERATE. 

If you get out, please share avalanche, snowpack or weather observations via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

In the last week, the mountains around Island Park received 2 feet of snow. Winds blowing 20-30 mph continue to transport recent snow into thicker slabs where human-triggered avalanches are likely. Avoid steep, wind-loaded slopes, and assess the snowpack for instability related to a slab sitting on a weak layer before considering riding or skiing non-wind-loaded slopes.