GNFAC Avalanche Forecast for Mon Mar 17, 2025
<p>Very dangerous avalanche conditions exist in the mountains of Island Park, West Yellowstone and Cooke City. Natural and human-triggered avalanches are likely. Avoid slopes steeper than 30 degrees and lower-angle terrain in the runout zones of avalanche paths.</p>
<p>Slides will fail within the new and wind-drifted snow as <strong>wind slab </strong><span>and</span><strong> storm slab avalanches. </strong>Since Thursday, the mountains in Island Park have received 40” of snow, equal to 4.1” <a href="https://avalanche.org/avalanche-encyclopedia/#snow-water-equivalent-swe… water equivalent (SWE)</span></a>. During the same period, the Lionhead area received 30” of snow and Cooke City received 24” of snow. Yesterday, hurricane-force gusts up to 100 mph transported snow into unstable slabs at all elevations (the strongest gusts were recorded on Lionhead Ridge).</p>
<p>In the Lionhead area, <strong>persistent slab avalanches </strong>breaking 3-5 feet deep on the weak snow buried in late January are possible. Slides on buried weak layers tapered off a couple of weeks ago, but heavy loading from recent snow could wake these layers up, resulting in large avalanches failing deep within the snowpack.</p>
<p>The specifics of weak layers and types of avalanches are irrelevant today. All can be large enough to injure or kill riders and skiers. Avoidance is critical.</p>
<p><span>The avalanche danger is HIGH on all slopes.<span> </span></span></p>
<p>Dangerous avalanche conditions exist in the Bridger, Southern Madison and Southern Gallatin Ranges, where 20-24” of snow has fallen since Thursday, and strong winds built unstable slabs of drifted snow. Human-triggered <strong>wind slab avalanches</strong> breaking 2-3 feet deep are likely. Yesterday, Alex and I avoided the steep terrain in Tepee Basin, where we measured two feet of recent snow and saw failures within and below the new snow (<a href="https://www.youtube.com/watch?v=VpFFY3Gug0w"><strong><span>video</span>…;). A warming trend yesterday is likely to result in increased instability within layers of the storm snow and <strong>storm slab avalanches</strong>.</p>
<p><strong>Persistent slab avalanches</strong> breaking 3-5 feet deep on the weak snow buried in late January are possible in the Southern Gallatin and Southern Madison Ranges. On Friday, a snowmobiler triggered a 2-3 foot deep hard slab on a steep slope with a relatively shallow snowpack in the Taylor Fork (<a href="https://www.mtavalanche.com/node/34610"><strong><span>video, photo and obs</span></strong></a>). With the heavy loading from recent snow, we could see an increase in larger avalanches.</p>
<p><span>To enjoy a safe day in the mountains, cautious route-finding that largely avoids steep slopes and runout zones is essential. The avalanche danger is CONSIDERABLE on all slopes.<span> </span></span></p>
<p>Since Thursday, the Northern Madison and Northern Gallatin Ranges have received 11-19” of snow (0.8-1.1” SWE). Strong winds scoured some slopes and loaded others, where <strong>wind slab avalanches </strong>breaking 1-2 feet deep are the primary concern. Yesterday, Mark and his partner triggered small drifts on test slopes (<a href="https://www.mtavalanche.com/node/34624"><strong><span>photos and details</span></strong></a>). Seek out slopes sheltered from the wind for better snow and safer avalanche conditions.</p>
<p>On non-wind-loaded slopes, <strong>loose snow avalanches</strong> are possible. While relatively harmless in open terrain, they can be dangerous above cliffs, rocks, or trees.</p>
<p><span>Identify and avoid unstable wind-loaded terrain by watching for a textured or pillowy snow surface, cracking or a stiffening of the snow surface. The avalanche danger is MODERATE. </span></p>
Weather and Avalanche Log for Mon Mar 17, 2025
Warming trend in the south - upside-down snow. Peak Gust: 100 mph on LH Ridge
AVALANCHE WARNING: Island Park, Lionhead, Cooke City
New Snow at Storm Castle
Not much snow on storm castle road until 5500 feet, started snowing at about 6500 feet, wind didn’t start blowing from the south until after 12:00pm Got CT5 on a layer buried 8cm on a North facing slope at about 7200 feet, Another layer broke after just above the ground at CT23. Snow depth was 110 mm.
Wind Slabs in Frazier Basin
From obs: Winds in the Frazier Basin zone were stronger than expected with moderate to strong gusts at the ridge, increasing through the day.
We noticed two large windslab pockets that had released since yesterday’s snow. One at the base of Hardscrabble Peak on a N aspect, the other in one of the SE facing gullies that access the Peak 9299/Hollywood Headwall ridge (see photo).
We rode into Tepee Basin and to the north wilderness boundary. There was 1.5-2 feet of new snow that fell since Thursday. We dug (3) snowpits on northeast, north and southeast slopes, between 8800'-9200'. The pits on northerly slopes had ECTP 17 and 22 on a thin weak layer below the new snow. We also had ECTP 6 within the storm snow. Photo: GNFAC
Forecast link: GNFAC Avalanche Forecast for Mon Mar 17, 2025
New snow and wind in Tepee Basin
We rode into Tepee Basin and to the north wilderness boundary. It was snowing all day with moderate winds and some strong gusts in more open areas. We could only slightly see the bottom of some avalanche path, but did not see any signs of avalanches (there could have been some higher up in terrain obscured by clouds.)
There was 1.5-2 feet of new snow that fell since Thursday. We dug (3) snowpits on northeast, north and southeast slopes, between 8800'-9200'. The pits on northerly slopes had ECTP 17 and 22 on a thin weak layer below the new snow. We also had ECTP 6 within the storm snow.
There was minimal cracking across the surface in the new snow, but plenty of signs of fresh drifts. It felt likely you would easily trigger storm slab or wind slab avalanches on steep slopes.
Isolated Wind Slabs in S. Bridger Range
From email: Isolated wind slabs today in the southern Bridgers.
Isolated wind slabs today in the southern Bridgers. Photo: E. Selinger
Isolated Wind Slabs in S. Bridger Range
From email: Isolated wind slabs today in the southern Bridgers.
Small wind slabs on Buck Ridge
Up to a foot of soft snow which seemed to have included a few inches from last weekend. Winds were transporting snow across Buck Ridge all day long.
We triggered two small and shallow wind slabs that didn't go anywhere, but they were a warning of bigger wind slabs on bigger slopes. We didn't find any faceted or weak layers of concern in the snowpack.
Wind slabs will grow in size overnight and will be the main concern tomorrow. Fortunately they will be easy to see an avoid.