Snow Observations List

Last Sunday we saw people touring up Scotch Bonnet and when we returned Monday we saw a large slide covering most of their tracks. 

Accessed low angle settled powder runs via mellow ridge terrain adjacent to a known avalanche path which is steep, rocky and windloaded. We descended on lower angle terrain following uptrack. On second lap observed the crown and debris while climbing uptrack and suspected we remote triggered; it was not there on first lap. Slope angle 35-38 degrees estimated. Estimate crown depth 60-120 cms. Estimated debris depth 2-3 meters due to terrain trap of an abrupt transition to flat terrain at bottom of path. We did not approach the crown or debris due to hangfire. Starting Zone NE facing at 9100' on wind loaded convexity with unsupported terrain below and rocky bed surface and exposed rocks/cliffs. I would classify it as HS-ASur-R4-D2.5-O

Large collapses with cracks connecting weak spots in the snowpack for 50 feet around us while breaking trail. Slab has gotten quite a bit thicker and more cohesive with 3 inches SWE in past 14 days combined with relatively warm temps promoting settling, strong solar input on the southerlies, and some wind. Average snow depth 100 cms consisting of a F-1Fslab on top of 20-30 cms of large facets. A crust in between on solar aspects. There is a density break/layer of NSF in the slab you can see in some of the photos where it appeared to shear between those layers. A very scary snowpack even for the Pioneers which regularly harbor PWLs throughout the season.

While transitioning at the top of mineral mountain burn, a member of our party stepped away from our packed out transition spot and likely the deeper impact from his ski boots triggered the weak layer beneath us and created a massive whumf that propagated hundreds of feet and was strong enough to knock snow off of nearby trees. Nothing we observed slid but the collapse was extremely evident. 

From the approach trail to Mummy II we saw two large crowns on the ridge associated with Mt. Bole. Not sure when they happened, but they looked pretty big! Observed Monday morning, February 19

 the snow is still bad! We were on top of bacon rind in the YNP, and dug a pit for fun and education of one of our party members. Experienced some BIG whoomphs on the way up and got very unstable scores. A Q2 CT19 and ECTP24, both around 85cm down into the snow pack (on the top of the very faceted layer we're seeing all over the advisory area. 

Best,

Joe

Centennial range blue and Wilson creeks. Did not see any signs of avys , or snow collapsing or whooping. Riders were on exposed slopes steeper than 30 degrees on all aspects high marking. It seems the centennial range has A more stable pack than other advisory areas. Although did not evaluate snow pack or dig pit, we stayed in low angle terrain 

From email: "Noted several 1-2 day old dry loose in steep terrain above the cliffs to the lookers left of Hang Ten. Also A large avalanche. crown propogated through the cliffs and looked to be about 200' wide and 1 1/2-2 ft. deep. Debris was no longer visible so I suspect this ran sometime during or shortly after the storm. (02/15)." 

From email: "Photo natural avalanche on a NW aspect at 9000', taken north of Cooke City today. It likely happened right around Feb. 15th."

Went touring up Pebble Creek today and got multiple whumpfs/large collapses when stepping off the skin track.

• Widespread stubborn collapsing, often triggered by 3 or 4 person on the slope.
• Numerous small D.5 loose dry observed in steep terrain.(mostly likely occuring in the last 24 hours)
• 12" to 14" reactive wind loaded protect on the east side of  ridge tops 
• Propagation in extended collum test found on multiple aspects at 9000ft
• Light to moderate winds out the west
• Consistent snow through out the day S1 to s2 

Avoiding avalanche terrain remains our risk mitigation strategy in Cooke City (2/18). We investigated a large avalanche on the north side of Scotch Bonnet that ran 400 vertical feet, broke 400 feet wide, and failed 5 feet deep. You would need to get lucky to survive getting caught in a slide that size, and triggering them is likely on slopes steeper than 30 degrees. There was a small avalanche on a steep rollover below the toe of the debris. Digging in their flank and crown, respectively, we found that they both failed on the layer of surface hoar. This was interesting in that there was well-preserved surface hoar at upper elevation slopes often exposed to the wind. However, the actual failure point is somewhat irrelevant, given the multiple weak layers in close proximity within the snowpack. 

Several naturals observed from the past few days. Large collapse on a NE 25 degree slope 

Toured west of Cole Creek outside RLM boundary.  Experienced multiple collapses and cracking.  Unsupportable surface with facets at the base of snowpack.  Stability tests resulted in multiple ECT with propagation. Dug pits in location with previous wind loading HS=141, not as deep on adjacent aspects.  

No natural avalanches observed.  See attached snowpilot profile.  

Toured up to Flanders today. Variable snow but stable conditions on the main route to the SE Bowl. Large natural avalanche on the NE face south of Flanders. 

NE aspect, 7400 ft. ECTP 14. PST 25/100

We rode out Buck Ridge to Muddy Creek and towards Cedar Mtn.. We went to look at the large avalanches riders remotely triggered yesterday. In addition to three previously reported avalanches, we saw at least eight recent avalanches that were not previously reported and appeared to have occurred at various times over the last 1-3 days, natural and/or remote triggered by riders. A group in the parking lot mentioned seeing many slides actively happen in this area on Friday, and a couple slides looked crisp enough to have occurred within the last 12-24 hours. We saw at least six recent slides in Muddy Creek, two in McAtee Basin, and one in Second Yellow Mule. Most were 2-3' deep hard slabs, ranging from 50'-500' wide.

We also saw a fresh avalanche that we either triggered from 750-800 feet away or it broke naturally. This avalanche happened when we were riding near the larger of the two avalanches from yesterday, on the south side of Cedar Mtn. When we regrouped at the base of the recent avalanche I was scanning all the nearby slopes and did not see any fresh avalanches, and noted a huge cornice on a low convex slope. We then rode up and parked near the top of yesterday's slide, and Doug noticed a fresh slide on the slope I had just been starring at. It was a wind-loaded slope, actively loading. The avalanche was ~130' wide with 100' of 4-12" deep new snow/wind slab and 30' wide broke almost 3 feet deep on weak snow near the ground.

Skies were overcast to partly sunny. Wind was light to moderate from the southwest-west. It snowed lightly on and off all day. There was about 1" of new snow at noon at 9,000'.

All the recent large avalanches and a freshly triggered avalanche are clear signs that the snowpack is dangerous and people should avoiding riding on and below steep slopes.

From IG 2/18/24: “Human triggered slides in cooke yesterday.”

From IG: 2 avalanches from either this morning or yesterday at the bottom of Skyline ridge 2’ at the crown

We were a group of 12 riders skiing the ghost trees up Sheep. We had a safe crossing of the bottom of the large avy slope (south west side of Miller) before skinning up the ghost slope. 
There was 3 other parties, one group of 8, one of 2, and one of 3-4. A few whomps were heard/felt skiing without any propagation or slides on the slope we skied. We did see a few point release slides high up on Miller Ridge later in the afternoon, after the sun had been baking that slope all day. 
The skiing in the Ghost trees was great! Even with all the people. 
we did talk to the group of 3/4. Earlier in the day, they had skinned further up the drainage and climbed up a  west facing rib of Miller proper. On the first steeper slope while skinning up they experienced large snow settling and bailed. 
we could see their tracks, and there actually was a different group that had climbed even higher and skied. We didn’t see any slide activity on the slope they skied. 

On our skin out at 4:30 or so, we could feel the southwest facing snow was definitely sun affected from the solar bake.

Lots of natural activity up buck ridge. The one photoed looked like it popped off this morning. Most activity we saw seemed to be on northern facing aspects