Weather and Avalanche Log for Fri Dec 23, 2022
Temps climbed overnight to single digits F
Temps climbed overnight to single digits F
On 12/22/22 there were many relatively large recent natural wind slabs in Yellowstone (4-5 that I saw). Photo: GNFAC
Natural avalanche on Amphitheater peak appeared to involve recent storm snow. Photo: GNFAC
While driving from Cooke through Yellowstone saw a couple recent natural slab avalanches. One on Amphitheater peak appeared to involve recent storm snow. And there were many relatively large wind slabs in Yellowstone (4-5 that I saw).
While driving from Cooke through Yellowstone I saw a couple recent natural slab avalanches. One on Amphitheater peak appeared to involve recent storm snow. And there were many relatively large wind slabs in Yellowstone (4-5 that I saw).
We found lots of weak snow waiting for a load on NE aspects up Dudley Creek. There was surprisingly little wind effect.
From obs "I skied on the east side of the Bridgers south of the ski area today. We dug a pit on an east aspect around 7300' and found 80 cm of snow with a similar structure to the more southerly parts of the advisory area. Well developed 2mm FC with a few DH cups sprinkled in made up the lower 40 cm or so of the snowpack (ECTP 21 on this layer) with the remainder consisting of 4F to F+ DFs. There was a razor thin "wind skin" I felt while skiing in more open areas below treeline but no major wind loading was present until at or near the ridgeline (pretty robust cornice development already for this time of year though). On our way back up just below the ridge around 7700' I felt a very large collapse that radiated out from my skis and shook some snow off of nearby branches."
<p><span><span><span><span><span><span>By yesterday morning 20+” (1.5” </span></span></span></span></span></span><a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/null/?cid=nrcseprd1314… water equivalent</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>, SWE) of snow fell in Cooke City. Ian caught sight of a natural avalanche billowing over the cliffs on Republic Mountain from the door of the Super 8 (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/22/natural-avalanche-running-republi…;). Dave and he rode around and saw wind moving snow and also had a collapse/whumpf under the new snow as they skied. Ian’s </span></span></span></span></span></span><a href="https://youtu.be/TKcVX1GITic"><span><span><span><strong><span><u><span>… </span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>explains that decision-making was easy because new snow, wind, weak layers, and a natural avalanche were a big red flag to stay out of avalanche terrain. His advice still applies today. Triggering avalanches remains likely and the danger is rated CONSIDERABLE on all slopes.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>In the last 48 hours the Lionhead area and southern ranges picked up 11” of snow (.5” SWE). Last night temperatures were -28F. Wind has lessened out of the NW and active wind-loading has too. The southern mountains have weak, sugary snow (facets) under a cohesive slab (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/22/hebgen-lake-ectp-26"><span><span>…;) that is breaking in our stability tests after thumping it with a fair bit of force (</span></span></span></span></span></span><a href="https://youtu.be/RNMts6wt0JQ"><span><span><span><strong><span><u><span>… Lake video</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). Thinner spots are where it’s easier to trigger slides because the weak snow is connected across a slope. Be thoughtful about getting into avalanche terrain and avoid it if there are signs of instability like collapsing or cracking. Triggering avalanches remain possible and the avalanche danger is rated MODERATE. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>The northern mountains had up to 5” of new snow by daybreak yesterday. Strong wind blew that into drifts and on Tuesday a skier noticed a shallow wind-slab avalanche in Beehive Basin (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/27278"><span><span><span><strong><span…;). There is also weaker snow in the lower half of the snowpack which is showing occasional signs of weakness in our tests. In the last 7 days we’ve either been to or had </span></span></span></span></span></span><a href="https://www.mtavalanche.com/snow-observations-list"><span><span><span><…; from </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/22/hebgen-lake-ectp-26"><span><span>… Peak</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/27282"><span><span><span><strong><span… Basins</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>, the </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/27237"><span><span><span><strong><span… Bridger Range</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span> and </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/27215"><span><span><span><strong><span… Creek</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>. These all have weak, sugary facets as a common denominator. Frigid temperatures grow and weaken these crystals even more. You may not see signs of instability other than triggering a slide, so dig, test and assess the snowpack before committing to a slope. For today, triggering avalanches remains possible and the danger is rated MODERATE. </span></span></span></span></span></span></p>
<p><span><span><span><span><em><span>If you get out, be prepared for the unexpected. The slightest mistake or injury can be life-threatening in these arctic temperatures. </span></em></span></span></span></span></p>
<p><span><span><span><span><span><span>Please share avalanche, snowpack or weather observations via our</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/add/snow_obs"><span><span><span><span>…; </span></span></span></span></span></span><span><span><span><strong><span><u><span><span>website</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>, email (</span></span></span></span></span></span><span><span><span><strong><span><span>mtavalanche@gmail.com</span></span></strong></span></span></span><span><span><span><span><span><span>), phone (406-587-6984), or Instagram (#gnfacobs). </span></span></span></span></span></span><span><span><span><span><span><span> </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>In the last 48 hours 6” of snow has fallen. Wind is also strong and drifting snow. Weak, faceted snow is underneath thicker slabs and wind-drifting adds weight on top of the weak snow. Triggering avalanches on these slopes is likely. Stay clear of thicker drifts and tune in to signs of instability like whumpfing (collapsing) as you ride or ski, or shooting cracks, both telltale signs that you can trigger a slide.</span></span></span></span></span></span></p>
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Overnight lows reached -39F at Bridger Ridge
On 12/21 we observed the remnants of a small natural avalanche (probably failed last night) on Scotch Bonnet immediately to the north of the Rasta Chutes. Approx 100 ft wide and ran 200 vertical ft.