GNFAC Avalanche Forecast for Sat Feb 15, 2025
<p><span><span><span><span><span><span>With new snow overnight, </span></span></span></span></span></span><span><span><span><strong><span><span>Wind slab avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> are the primary concern today. Be on alert in places where you find a lot of new snow. Remote weather stations indicate that the deepest snow (in localized areas around Big Sky) is low density (~5%) and I don’t expect it to form cohesive slabs and avalanche by itself - but even a little wind effect could tip the scales and make it reactive and quite dangerous. Without wind, in the deeper areas, watch for </span></span></span></span></span></span><span><span><span><strong><span><span>Dry Loose avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> (sluffs) that could be fairly sizable in steep terrain.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Riders triggered thin Wind Slabs up Storm Castle Creek yesterday (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34169"><span><span><span><span><span><…;) and there were quite a few small Wind Slabs triggered on Thursday (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34160"><span><span><span><span><span><…. Bridger’s observation,</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span> </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34144"><span><span><span><span><span><… fork of Hyalite observation</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34137"><span><span><span><span><span><…. Blackmore observation</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>). New snow could mask signs of these older drifts as well as pile up a load on top of them and keep them reactive. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Watch for areas of wind drifted snow and signs that the drifts are unstable (chiefly recent avalanches or cracking). Assess how well wind slabs have bonded to the old snow before getting onto steep slopes.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>The avalanche danger is MODERATE today.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Snowfall totals are not very impressive around West Yellowstone, Island Park and Cooke City and there hasn’t been a ton of wind. As with further north, freshly formed </span></span></span></span></span></span><span><span><span><strong><span><span>Wind Slabs</span></span></strong></span></span></span><span><span><span><span><span><span> are the primary concern, but they will be less widespread and not as thick. Look out both for thin fresh drifts and somewhat thicker older drifts that formed during the high winds mid-week. </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>are the wild card in these areas. There hasn’t been a ton of activity on the weak layer that formed towards the end of January, but there has been some (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34156"><span><span><span><span><span><… photo</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/cornice-triggered-avalanche-miner… City photo</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>, </span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=wZ3k35z5Ej8&embeds_referring_euri=h… Fork video</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>). These slides are most likely to be triggered on windloaded slopes, where slabs are more cohesive and thicker. If you do trigger one of these slides it’ll break deeper, wider and be more dangerous. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>The avalanche danger is MODERATE.</span></span></span></span></span></span></p>
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Thin and Weak Snowpack
We toured into Specimen Creek today and rode on E-SE and W aspects. Though more snow exists in this location than is typical, the snowpack here is still shallow and weak.
Our snow profile on a W aspect at 8100' showed us some of the weakest snow structure we had seen this season. Sugary, large-grained facets and depth hoar spilled out of the pit wall at the ground. In this location, a 6" slab sits atop this weak snow, but was not cohesive enough to get unstable test results (HS: 90, ECTX).
Outside of very weak structure, no other signs of instability like cracking, collapsing or recent avalanches were spotted.
While the state of the snowpack now provides better coverage and riding than usual, expect to see a jump in avalanche danger on these shallow, weak slopes when/if they receive another good round of snowfall.
Wind Slab Avalanches, Storm Castle Creek
Sledded up storm castle. Spent the majority of the day skinning and skiing NE to NW aspects. Found debris from multiple R1-D1 wind slabs from earlier this week. Found widespread but inconsistent wind slabs (2"- 6" thick) at elevations 6700' to 8400'. Throughout the day cracking and collapsing was noticed multiple times on areas of stiffer snow. Snow quality changed dramatically from powder turns to thick wind crust with no visual surface difference.
Wind Effected Snow North of Cooke
4-6’’ wind slabs cracking on test slopes on W aspects at upper elevations today
Small wind slab avalanches in south cottonwood
Toured up around Blackmore and s cottonwood. Found an extremely reactive windslab in the afternoon. It was thin, but easily triggered and would propagate about the width of each terrain feature (20-50ft). Each slab ran the length of the slope (150-200 ft).
Toured up around Blackmore and s cottonwood. Found an extremely reactive windslab in the afternoon. Photo: J Alford