GNFAC Avalanche Forecast for Wed Feb 19, 2025
<p><span><span><span><span><span><span>There is simply a lot of snow and riding conditions are as good as it gets; however, remember that most avalanches happen within 24-48 hours after snowfall or wind.</span></span></span></span></span></span></p>
<p><span><span><span><strong><span><span>Wind slabs</span></span></strong></span></span></span><span><span><span><span><span><span> - In all areas, the primary avalanche problem is wind slabs as Dave found </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34254"><span><span><span><span><span><… Island Park </span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>and a skier found on </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34251"><span><span><span><span><span><… Peak</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span> yesterday where a wind slab broke 18 inches deep, 50 feet wide and ran a significant distance. Winds yesterday from the NW did most of the drifting, and winds shifting to the SW today may find a little snow to move. Fortunately there are many slopes unaffected by winds.</span></span></span></span></span></span></p>
<p><span><span><span><strong><span><span>Storm slabs</span></span></strong></span></span></span><span><span><span><span><span><span> - The new snow should be bonding to itself and stabilizing quickly, but there is just a lot of powder out there creating some uncertainty. Because there’s still a possibility of storm slabs, I’d select terrain with a clean runout today free of terrain traps, rocks, and trees if getting onto steeper slopes.</span></span></span></span></span></span></p>
<p><span><span><span><strong><span><span>Persistent slab avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> - A problem in the Lionhead area, southern Madison Range (Taylor Fork, Teepee, Carrot, etc.) and southern Gallatin Range. The problem layer is small facets that formed in late January, now buried 2-3 feet deep. The Cooke City area may still have this problem, but it is buried deeper and seems to be less of an issue. A snowmobiler was caught in a </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34154"><span><span><span><span><span><… persistent slab avalanche on Lionhead</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span> on Thursday BEFORE all this snow fell. The most likely places to trigger one of these slides is on a slope with extra loading from yesterday’s winds, but I think there will still be slides on this layer on non-wind loaded slopes that will surprise you..</span></span></span></span></span></span></p>
<p><span><span><span><strong><span><span>Travel advice today</span></span></strong></span></span></span><span><span><span><span><span><span> - Stay off slopes or portions of slopes with fresh wind drifting. Consider the consequences of triggering a soft storm slab avalanches even though the likelihood of these slides is going down. If traveling in areas with a persistent slab avalanche problem, I’d simply avoid avalanche terrain for now and give the faceted layer time to stabilize. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>The avalanche danger in all areas is CONSIDERABLE in places with fresh wind loading where you will trigger a slide.. The danger is MODERATE on all other slopes not loaded by recent winds</span></span></span></span></span></span></p>
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Weather and Avalanche Log for Wed Feb 19, 2025
Strongest winds Tuesday morning/midday NW
Wind Slab Instability
We got lucky in the Centennials with great snow and good visibility. There was about 20" of new snow from this weekend's storm. We covered 35 miles of backcountry riding and got eyes on a lot of avalanche terrain from lower elevation slopes, to Jefferson Bowl, the terrain in and above Hellroaring Creek, and East Hotel Creek. We didn't see any avalanche activity. However, we observed shooting cracks in drifts and triggered small wind-loaded slopes and cornices. So, human-triggered avalanches on wind-loaded slopes are likely.
We dug three quick pits but prioritized getting eyes on terrain over in-depth snowpack analysis:
Low-elevation slope on Sawtelle - NE @ 7600' on a slope with no wind effect: ECTX in a 160 cm deep pit
Above Hellroaring - S @ 8400' on a wind loaded slope: ECTP1 6" deep (wind slab) and ECTP21 20" deep (wind slab)
Arange - SW @ 8700' non-wind-loaded slope: ECTP21 20" deep on facets below a melt-freeze crust
Travel Advice:
- Avoid wind-loaded slopes
- While stability on non-wind-loaded slopes seemed good, it snowed a lot. So, I would either carefully assess for instability in the upper 3 feet of the snowpack with an ECT , or I would give it a few days to settle out before getting on steeper, non-wind-loaded slopes.
The danger was CONSIDERABLE on wind-loaded slopes (human-triggered avalanches likely) and MODERATE in non-wind-loaded terrain (human-triggered avalanches possible).
Cornice triggered natural avalanche, Saddle Peak
Cornice broke in between north and south saddle peaks. The initial propagation width was hard to distinguish. Maybe 50 feet. About 18 inches deep at height of crown.
Skied down Rocky Rib and then into south east facing trees that follow the path. At the Argentina/ Shushmans traverse elevation there was a visible 2 foot wall and the slide had continued over the roll below.
Cornice broke in between north and south saddle peaks. The initial propagation width was hard to distinguish. Maybe 50 feet. About 18 inches deep at height of crown. Photo: Anonymous
Forecast link: GNFAC Avalanche Forecast for Wed Feb 19, 2025
Cornice triggered natural avalanche, Saddle Peak
Cornice broke in between north and south saddle peaks. The initial propagation width was hard to distinguish. Maybe 50 feet. About 18 inches deep at height of crown.
Skied down Rocky Rib and then into south east facing trees that follow the path. At the Argentina/ Shushmans traverse elevation there was a visible 2 foot wall and the slide had continued over the roll below.
Wind slabs, cornice collapses on Mt. Blackmore
2/17 Immediately noticed signs of wind loading and wind slabs on NE-E aspects once in the basin. New cornices have formed in the last couple days along the North ridge to the summit. Cornice collapse on the summit triggered a small wind slab on an isolated slope.
From obs: "2/17 Immediately noticed signs of wind loading and wind slabs on NE-E aspects once in the basin. New cornices have formed in the last couple days along the North ridge to the summit. Cornice collapse on the summit triggered a small wind slab on an isolated slope." Photo: R. Rintala
From obs: "2/17 Immediately noticed signs of wind loading and wind slabs on NE-E aspects once in the basin. New cornices have formed in the last couple days along the North ridge to the summit. Cornice collapse on the summit triggered a small wind slab on an isolated slope." Photo: R. Rintala