20-21
Shooting cracks near Cooke City
From obs: "Extremely touchy snowpack in the pebble creek drainage. Nearly constant collapsing and cracks were shooting very long distances. Snowpack was definitely sending a clear message!"
Collapse/Crack on Scotch Bonnet
From obs: "While skinning up the south shoulder of Scotch Bonnet, about half way (~10,000 ft.) shooting cracks occurred on convexities and were accompanied by whumpfing. While traversing a slope a crack shot perpendicular to the slope at a convexity about 60 ft. up and the whole slope collapsed. After this we immediately turned around taking the most conservative path. These conditions were not present lower down the slope and a snow pit showed no propagation with only a Q3 fracture on the recent layer of surface hoar . It seemed that the higher elevation and more southern aspect decreased the stability of the recent surface hoar layer. The surface hoar layer was not reactive on more westerly slopes."
GNFAC Avalanche Forecast for Mon Jan 18, 2021
<p>Current snowfall is favoring the northern Gallatin Range with 6” of new snow this morning (0.6” snow water equivalent) with more forecast to fall today. This snow is falling on a weak snowpack and creates dangerous avalanche conditions. Human triggered avalanches are likely and natural avalanches are possible. Avoid travel on and underneath steep slopes. The avalanche danger is CONSIDERABLE.</p>
<p>The Bridger Range and mountains near Big Sky got an inch of snow yesterday. More snow today with moderate northwest wind will form fresh slabs on a weak snowpack. Weak, sugary snow near the ground, buried 2-3’ deep has produced large human triggered and natural avalanches over the last couple weeks (<a href="https://www.mtavalanche.com/avalanche-activity"><strong>avalanche log</strong></a>). Additionally, a layer of weak, feathery surface hoar is buried 3-6” below recent snow. Where today’s new snow is drifted into thicker slabs it will avalanche easily on the surface hoar layer, and avalanches can break deeper on sugary snow near the ground (<a href="https://www.youtube.com/watch?v=5hQdnhL3jRo&list=PLXu5151nmAvQDzKmH…;). Avalanche danger is CONSIDERABLE on wind-loaded slopes and MODERATE on all other slopes.</p>
<p>Near Cooke City, 4” of new snow this morning (0.4” SWE) with more snow and wind today will grow thicker slabs over recently buried surface hoar. Dave rode north of Cooke yesterday and found this surface hoar layer which he discuses is his <strong><a href="https://www.youtube.com/watch?v=-AhOAQTfkHE&list=PLXu5151nmAvQDzKmH…;. Over the weekend skiers got collapsing with long shooting cracks (<strong><a href="https://www.mtavalanche.com/images/21/shooting-cracks-scotch-bonnet">ph…;, <strong><a href="https://www.mtavalanche.com/images/21/shooting-cracks-near-cooke">photo…;), and triggered a small slab on this layer (<a href="https://www.mtavalanche.com/images/21/ski-cut-small-slab-sh"><strong>ph…;). An additional concern is weak, sugary snow buried 2-3 feet deep which makes larger avalanches possible. These weak layers are not on every slope, so it is worth digging to check for them and track their distribution and stability. With snow and wind adding weight to the snowpack today, avoid steep wind-loaded slopes. Carefully assess the snowpack before riding any steep slope. Avalanche danger is CONSIDERABLE on wind-loaded slopes and MODERATE on all other slopes.</p>
<p>The mountains south of Big Sky to West Yellowstone have one inch of new snow and will receive a couple inches of snow today. With minimal loading, the chances have decreased for triggering an avalanche on weak snow near the ground, but this snow is slow to gain strength. Even a little snow today will add weight to an unstable snowpack. Travel in avalanche terrain requires thorough snowpack assessment and cautious terrain selection. The best strategy is to avoid travel on and underneath slopes steeper than 30 degrees. Large avalanches are possible to trigger and danger is MODERATE.</p>
<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>
Upcoming Avalanche Education and Events
See our education calendar for an up-to-date list of all local classes. Here are a few select upcoming events and opportunities to check out:
From obs: "While skinning up the south shoulder of Scotch Bonnet [on 1/15/21], about half way (~10,000 ft.) shooting cracks occurred on convexities and were accompanied by whumpfing. While traversing a slope a crack shot perpendicular to the slope at a convexity about 60 ft. up and the whole slope collapsed. After this we immediately turned around taking the most conservative path. These conditions were not present lower down the slope and a snow pit showed no propagation with only a Q3 fracture on the recent layer of surface hoar..." Photo: M. Dvorsak
Forecast link: GNFAC Avalanche Forecast for Mon Jan 18, 2021GNFAC Avalanche Forecast for Tue Jan 19, 2021
From email: "Extremely touchy snowpack in the pebble creek drainage [on 1/16/21]. Nearly constant collapsing and cracks were shooting very long distances. Snowpack was definitely sending a clear message!" Photo: J. Zimmerer
Forecast link: GNFAC Avalanche Forecast for Mon Jan 18, 2021GNFAC Avalanche Forecast for Sat Jan 23, 2021
Look for a distinct stripe in the wall of your snowpit 0.5-1.5' beneath the snow surface to identify a buried layer of weak surface hoar. Photo: GNFAC