22-23

Natural avalanches near Cooke and YNP

Yellowstone Park NE
Cooke City
Code
HS-N-R2-D1.5-S
Elevation
7500
Aspect
E
Latitude
45.00340
Longitude
-110.04300
Notes

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).

Number of slides
5
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Natural trigger
R size
2
D size
1.5
Bed Surface
S - Avalanche released within new snow
Problem Type
Wind-Drifted Snow
Slab Thickness
16.0 inches
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

Natural avalanches near Cooke and YNP

Date

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).

Region
Cooke City
Location (from list)
Yellowstone Park NE
Observer Name
Alex Marienthal

Weak Snow in Dudley

Date
Activity
Skiing

We found lots of weak snow waiting for a load on NE aspects up Dudley Creek. There was surprisingly little wind effect.

Region
Northern Madison
Location (from list)
Dudley Creek
Observer Name
Nicholas Westfall

Southern Bridger Collapsing

BRIDGER RANGE
Bridger Range
Code
Elevation
7700
Latitude
45.85120
Longitude
-110.94800
Notes

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."

Number of slides
0
Number caught
0
Number buried
0
Problem Type
Wind-Drifted Snow
Snow Observation Source
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Red Flag
Advisory Year

GNFAC Avalanche Forecast for Thu Dec 22, 2022

Snowpack and Avalanche Discussion

<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.&nbsp;</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.&nbsp;</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).&nbsp;</span></span></span></span></span></span><span><span><span><span><span><span>&nbsp;</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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Natural avalanche on Scotch Bonnet

Scotch Bonnet
Cooke City
Code
SS-N-R1-D2
Latitude
45.07330
Longitude
-109.94800
Notes

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. 

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
1
D size
2
Vertical Fall
200ft
Slab Width
100.00ft
Snow Observation Source
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year