24-25

Date

Sun, 12/22/2024 - 12:00

Activity

Skiing

Surprisingly shallow snow pack on the upper parts of Bacon Rind. South of Skillet area in the meadows. 2-3 foot depth max at 8800 on a SE aspect. 10+ inches of newer snow on top of a well developed surface hoar. A semi-supportable crust below that with facets to the bottom. ECTP 11 really surprised us, failing on the surface hoar. Challenging skiing staying on top and did some base damage on rocks even up high. Log jam roller coaster back down to the car. Still a fun outing. Send us snow! And keep up the good work!

Region

Southern Madison

Location (from list)

Bacon Rind

Observer Name

Tony Thatcher

Weak Snow at Lionhead

Date

Sun, 12/22/2024 - 11:10

Activity

Snowmobiling

We rode up Denny Creek to the local's route. Coverage was thin, but passable as we left the Denny and worked up through the trees. The trail hadn't been set in yet this season. We didn't go far once we arrived in the openings below the ridge because visibility was poor. No avalanches or red flags for instability observed (but poor visibility).

The snowpack was weaker than everywhere else Alex and I have been this year. The snowpack remains thin (60-80 cm). The post-Thanksgiving dry spell resulted in a well-defined layer of surface hoar and near surface facets. Below that the base of the snowpack transitioned to large grain sugary facets and depth hoar. Resting on all this weak snow was a cohesive slab. In the non-wind-loaded terrain where we rode, the snowpack seemed to have adjusted to the current load (ECTNs in the high teens to 20s, PST 30/100 arrest). However, new or wind-drifted snow would upset this delicate balance. We avoided wind-loaded terrain where avalanches would be most likely, though this was partially because our planned route simply didn't intersect with commonly wind-loaded slopes.

While snowpack tests were not propagating failure today, just a few inches of snow (over 0.3" SWE) would change the picture. The danger would increase and collapsing and human-triggered avalanches would become likely.

On the drive we saw one small wind slab in Yellowstone that looked 1-3 days old (photo attached).

Visibility improved on the drive back, with high clouds, and we looked towards Lionhead with Binoculars from the highway and did not see any avalanches.

Region

Lionhead Range

Location (from list)

LIONHEAD AREA

Observer Name

Dave Zinn

Propagation in ECTs, Rob's Knob

Date

Sun, 12/22/2024 - 10:15

Activity

Skiing

Snow surface soft with ~3" of new, mod-strong SW winds at 11am

Reactive tests in snowpits with low to moderate ECTP scores. HS 105, NE aspects at 9480'.

Experienced collapsing on the north end of Rob's, likely failing on buried surface hoar that was evident in pit.

Region

Cooke City

Location (from list)

Fisher Mtn.

Observer Name

BMG L1

Collapsing / Poor stability test scores, West Henderson

Date

Sat, 12/21/2024 - 11:05

Activity

Skiing

We toured above 9000' on a W to SW aspects on Henderson Mtn. We experienced several collapses and had propagation in multiple ECTs performed. HS varies between 85-105cm. Snowpilot pit is from 9820' W aspect, photo from 9940': both with ECTP results.

Snow surface variable with wind boards and radiation crusts, mixed with soft snow in shaded aspects.

Region

Cooke City

Location (from list)

Daisy Pass

Observer Name

BMG L1

GNFAC Avalanche Forecast for Sun Dec 22, 2024

Snowpack and Avalanche Discussion

Today a person can trigger large persistent slab avalanches that break on weak layers buried in the middle of the snowpack or near the ground. These persistent slab avalanches have become less likely since snowfall and strong winds ended late Wednesday, but the potential size and consequences remain large.

During the first half of this week strong winds drifted new snow into thick, heavy slabs (<a href="https://www.youtube.com/watch?v=w-aXzlPHrYA">… video</a>). On Wednesday there were multiple large natural avalanches near Cooke City (<a href="https://www.youtube.com/watch?v=zCdhitUHk1o">…;, <a href="https://www.mtavalanche.com/images/24/large-persistent-slab-avalanche-h… photo</a>, <a href="https://www.mtavalanche.com/images/24/persistent-slab-avalanche-fisher"… photo</a>), and an avalanche on Saddle Peak broke 1-3 feet deep (<a href="https://www.mtavalanche.com/node/32548"><span…;). On Tuesday Ian triggered an avalanche remotely (from lower angle terrain nearby) on Buck Ridge near Big Sky (<a href="https://www.mtavalanche.com/node/32497"><span…;), and on Friday a skier had a large collapse in the Bridger Range (<a href="https://www.mtavalanche.com/node/32582"><span…;).

Choose small, simple, non-wind-loaded slopes with clean runouts free of hazards like rocks, trees or cliffs. If you have any doubts about snowpack stability avoid slopes steeper than 30 degrees and be cautious of runout zones below.

Yesterday on Buck Ridge a snowmobiler triggered a 12” deep wind slab avalanche (<a href="https://www.mtavalanche.com/node/32601"><span…;). Strong winds last night might have formed fresh wind slabs, and a few potentially unstable drifts could remain from earlier in the week. Look for signs of wind-drifted snow and be cautious of wind-loaded slopes, especially where consequences of a slide are higher due to terrain traps.

Carefully and continuously assess the snowpack and terrain for avalanche potential, and travel one person at a time on steep slopes or through runouts. The avalanche danger is MODERATE.

Read more about GNFAC Avalanche Forecast for Sun Dec 22, 2024

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Snowmobiler triggered wind slab on Buck Ridge

Buck Ridge

Northern Madison

12/21/2024

Code

SS-AM-R2-D1.5

Elevation

9500

Aspect

Latitude

45.17190

Longitude

-111.38000

Notes

From email: "Rode buck today. It was very windy this week. Open areas are quite scoured, but there are still great stashes to be found if you hunt around. We triggered a 12" soft wind slab on a NE facing slope at 9.5k'."

Number of slides

Number caught

Number buried

Avalanche Type

Soft slab avalanche

Trigger

Snowmobile

R size

D size

1.5

Problem Type

Wind Slab

Read more about Snowmobiler triggered wind slab on Buck Ridge

Slab Thickness

12.0 inches

Vertical Fall

50ft

Slab Width

100.00ft

Images

Soft slabs on Buck

Snow Observation Source

Soft slabs on Buck

Slab Thickness units

inches

Single / Multiple / Red Flag

Single Avalanche

Advisory Year

24-25

Weather and Avalanche Log for Sun Dec 22, 2024

Read more about Weather and Avalanche Log for Sun Dec 22, 2024

Blue Creek snowpack

Date

Sat, 12/21/2024 - 19:10

Activity

Snowmobiling

ECTP 15 75cm up from ground. HS90-110 9000ft SE aspect. Down 1000 feet similar aspect we also got propagation up 23cm with a HS of 55cm. Photo from the 9000ft pit.

Region

Island Park

Location (from list)

CENTENNIAL RANGE

Observer Name

zach bailey