24-25

Whumpfing, Cracking and Avalanches at Bacon Rind

Date

Mon, 01/13/2025 - 00:30

Activity

Skiing

Travel conditions have improved significantly since the last time we were at Bacon Rind, unfortunately, avalanche conditions have not. Similar to what Dave and Alex saw yesterday in Lionhead, the snowpack on Bacon Rind is shallow and has well-developed persistent weak layers near the bottom of the snowpack.

While ascending the burn, we triggered so many thunderous collapses that we quickly lost count. These collapses shook snow off the trees around us and visibly dropped the snow surface beneath our feet. Near the top of the ridge, we saw a large avalanche (SS-N-R3-D2-O) that broke on a north facing aspect, around 2' deep, on weak snow near the ground. It was not clear whether it was one large avalanche or two that released sympathetically with one another. If one slide, this avalanche broke nearly 900' wide and slid around 1000' vertical. It broke during the most recent period of intense loading in this area, likely January 5th or 6th.

When we reached the top of the Skillet and dug a snowpit, we noticed that the upper portion of the path had cracked and shifted in numerous places but had not avalanched. Our snowpit on an east aspect showed a 2' dense slab on top of sugary facets and depth hoar. Our test result was ECTP 13. We also dug a pit on a south facing aspect and noted shallower snow that was slightly stronger than the other aspects we had seen thus far (north and east).

Given all these clear signs of instability, it was an easy decision to stick to terrain less than 30 degrees, including runout zones.

S-1 snowfall most of the day, with calm winds. Skies began overcast and cleared throughout the day.

Region

Southern Madison

Location (from list)

Bacon Rind

Observer Name

H. Darby

GNFAC Avalanche Forecast for Mon Jan 13, 2025

Snowpack and Avalanche Discussion

New snow from the weekend makes human-triggered avalanches likely. This new snow is in addition to more than 4-5 feet that fell over the last two and a half weeks (4-5” of snow water equivalent throughout the forecast area).

Recent winds, mainly out of the northwest and west, have drifted snow into thicker slabs that are easy to trigger. These wind slab avalanches can be 1-4’ deep and large enough to bury a person, and smaller slides can easily knock you over and be dangerous if they drag you into trees, over cliffs or pile deep in a narrow gully. Wind Slabs broke naturally on Friday (<a href="https://www.mtavalanche.com/node/33472"><… and photos</a>) and Saturday (<a href="https://www.mtavalanche.com/node/33503"><… and photo</a>), so expect drifts to break easily today.

The last 2+ weeks of snow built a thick slab and steadily added weight to weak layers at the bottom of the snowpack. This snowpack structure makes persistent slab avalanches possible. (<a href="https://www.mtavalanche.com/node/33442"><… of buried weak layers</a>). These slides could be triggered from shallower areas on a slope like near rock outcrops or wind-scoured ridges and propagate to where the snowpack is many feet deep (see <a href="https://www.youtube.com/watch?v=xHr_3Bdtq1o"><s…’s video from Blackmore</a>). Minimize the chances of these deeper slides by choosing slopes sheltered from wind-loading and with a generally uniform snowpack depth across the slope. Small slopes with clean runouts free of trees, rocks or gullies also greatly minimize the consequences of any size slide.

The avalanche danger is CONSIDERABLE on windloaded slopes and MODERATE on all other slopes.

Near Cooke City and West Yellowstone the primary concern is persistent slab avalanches breaking on weak layers near the bottom of the snowpack.

Over the last week near Cooke City, avalanches 4-6’ deep broke naturally or some were possibly triggered from flat terrain a long distance away (<a href="https://www.mtavalanche.com/images/25/fresh-persistent-slab-south-mt-ab…. Abundance photo</a>, <a href="https://www.mtavalanche.com/images/25/persistent-slab-above-henderson-b… Mtn. photo</a>, <a href="https://www.mtavalanche.com/images/25/older-persistent-slab-fisher-mtn-… Mtn. photo</a>). The most recent was reported yesterday on west Woody ridge (<a href="https://www.mtavalanche.com/node/33528"><… and photos</a>).

Near West Yellowstone and the southern Madison and southern Gallatin Ranges the snowpack is shallower, but the same poor structure exists. These mountains received less snow over the last week, but the shallower slab above the weak layer makes it easier to trigger avalanches 1-3’ deep and up to hundreds of feet wide. This was evident yesterday when Dave and I experienced a loud, rumbling collapse on a low angle slope as we exited our snowpit (<a href="https://www.mtavalanche.com/node/33529"><…; and <a href="https://www.youtube.com/watch?v=I6nDBNZli-Y"><s…; from yesterday).

Recent winds formed thick drifts which add weight to buried weak layers, and are a significant hazard on their own. Wind slab avalanches can be triggered where recent drifts formed and can be large enough to bury or injure a person (<a href="https://www.mtavalanche.com/images/25/deep-wind-slab-henderson"><… of recent wind slab avalanche</a>).

Avoid slopes steeper than 30 degrees, especially slopes with recent drifts, and give a wide berth to the flatter runout zones below steep slopes. Human-triggered avalanches are likely and the avalanche danger is CONSIDERABLE.

Near Island Park received less snow over the last week, and has a deeper snowpack than the nearby Lionhead and southern ranges which has helped weak layers near the bottom of the snowpack slowly become more stable (Dave’s <a href="https://www.mtavalanche.com/node/33433"><…; and <a href="https://www.youtube.com/watch?v=5jyQDWE32GI"><s…;). While it has become less likely, you can still trigger a persistent slab avalanche breaking 3-6’ deep on weak layers. Wind slab avalanches of recently drifted snow are also possible. Minimize the chances and consequences of a dangerous avalanche by choosing smaller slopes sheltered from wind-loading, with clean runouts free of trees, rocks or gullies. Or you can greatly reduce your chance of triggering an avalanche by riding on slopes less than 30 degrees steep. The avalanche danger is MODERATE near Island Park.

Read more about GNFAC Avalanche Forecast for Mon Jan 13, 2025

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Weather and Avalanche Log for Mon Jan 13, 2025

Read more about Weather and Avalanche Log for Mon Jan 13, 2025

Read more about Below Airplane Bowl Profile - 12 Jan 2025

Lionhead Range, 2025-01-12

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Collapsing and bad snow structure

Date

Sun, 01/12/2025 - 17:30

Activity

Snowmobiling

We rode below Lionhead Ridge via Denny Creek and found a snowpack with the worst structure we've seen in our forecast area. There was around 3 feet of snow on the ground between 8000-9000'. The bottom foot was sugary weak facets, and the upper snowpack was a supportable hard slab with new snow on top (profile attached).

We had two large collapses. The most significant collapse happened when we were leaving our snowpit and walking back to our sleds a few feet away. We heard a long "whumph" sound and saw our snowmobiles drop an inch, as the snowpack on the entire slope around us collapsed. Our snowpit had ECTP23 x2 breaking on the sugary weak layer.

We saw 4-5 avalanche crowns that were up to a week old, some had been reported and a few we had not heard of (3 pictured were previously not reported to my knowledge). One was a 3-4'+thick slab on a rocky heavily wind-loaded slope off Lionhead ridge, and the other two were ~2' deep on less wind affected slopes lower down in the trees, but probably had some previous wind-loading.

Despite no fresh avalanches the last few days, the poor structure and collapses suggest a person could easily trigger a large avalanche that breaks wide on the weak layers at the bottom of the snowpack.

There was evidence of recent winds in the meadows with thick drifts felt while riding and some ridges scoured free of recent snow. Skies were mostly clear and wind was calm today.

Region

Lionhead Range

Location (from list)

LIONHEAD AREA

Observer Name

Marienthal and Zinn

4-6' deep persistent slab avalanche on Woody Ridge

Woody Ridge

Cooke City

1/12/2025

Code

HS-N-R3-D3-O

Elevation

10000

Aspect

Latitude

44.97010

Longitude

-109.92700

Notes

Observed a large avalanche on a west facing slope approx 10000ft, with a higher crown at 10200'. Crown depth 4-6'. HS-Ns-D2-R2-O . Ran 1000ft and into terrain I had previously considered safe.

Number of slides

Number caught

Number buried

Avalanche Type

Hard slab avalanche

Trigger

Natural trigger

R size

D size

Bed Surface

O - Old snow

Problem Type

Persistent Weak Layer

Read more about 4-6' deep persistent slab avalanche on Woody Ridge

Slab Thickness

60.0 inches

Vertical Fall

1000ft

Images

Crown of avalanche on Woody Ridge 3

Crown of avalanche on Woody Ridge 2

Crown of avalanche on Woody Ridge

Avalanche on Woody Ridge

Snow Observation Source

Avalanche on Woody Ridge

Slab Thickness units

inches

Single / Multiple / Red Flag

Single Avalanche

Advisory Year