22-23

Date

Tue, 12/27/2022 - 15:00

Activity

Snowmobiling

Snowmobile club members texted me that they triggered a 3' deep slab, that ran 100 yds., from connected terrain in Frog Pond Basin. It sounded like a heavily wind loaded slope.

Region

Butte Area

Observer Name

Will Shoutis

GNFAC Avalanche Forecast for Fri Dec 30, 2022

Snowpack and Avalanche Discussion

Weak layers being loaded by more new snow and wind drifting make for dangerous avalanche conditions. There is a weak layer buried just beneath this week’s new snow and another in the lower third of the snowpack (<a href="https://youtu.be/F8HKebJ_OJA">… video</a>). Both layers have been overloaded by the new snow and will continue to be loaded with more new snow on the way today. Expect to trigger avalanches on these layers if you get onto steep slopes. You could also trigger a slide from below, so give steep slopes a wide berth if you’re crossing beneath them. Don’t try to outsmart the avalanche hazard - stick to mellow slopes where you’ll be able to safely enjoy the fresh snow. Human triggered avalanches are likely today and the avalanche danger is CONSIDERABLE.

Triggering large avalanches remains possible today. Slides can break on two weak layers, one  about a foot under the surface and another near the ground (<a href="https://www.youtube.com/watch?v=AzCUIW7Fr_0">… Fork video</a>). These layers were loaded by new snow over the past few days and winds have been drifting that fresh snow into thicker slabs. Avalanches broke naturally on these weak layers earlier in the week and the weight of a skier or rider could tip the scales to trigger similar slides today (<a href="https://www.mtavalanche.com/node/27377"><span… Basin avalanche</a>, <a href="https://www.mtavalanche.com/node/27387"><span… Peak avalanche</a>). The weak layer near the ground is somewhat less widespread near Cooke City, but is there in places and has shown itself to be dangerous (<a href="https://www.mtavalanche.com/node/27148"><… avalanche</a>). Look for signs of instability (cracking, collapsing, recent avalanches, poor stability test scores) and back off steep slopes if you find them. Tracks on a slope do not indicate stability - only that nobody has hit just the wrong spot yet. Even if you don’t see clear signs of instability, tilt the odds in your favor by riding one at a time and thinking carefully about the consequences of triggering a large avalanche before riding steep slopes. The avalanche danger is rated MODERATE.

Please share avalanche, snowpack or weather observations via our<a href="https://www.mtavalanche.com/node/add/snow_obs">…; website</a>, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

In Island Park, weak layers being loaded by more new snow and wind drifting make for dangerous avalanche conditions. Expect to trigger avalanches today if you get onto steep slopes. You could also trigger a slide from below, so give steep slopes a wide berth if you’re crossing beneath them. Don’t try to outsmart the avalanche hazard - stick to mellow slopes where you’ll be able to safely enjoy the fresh snow.

Read more about GNFAC Avalanche Forecast for Fri Dec 30, 2022

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.

Weather and Avalanche Log for Fri Dec 30, 2022

Read more about Weather and Avalanche Log for Fri Dec 30, 2022

Read more about Hebgen Lake Profile - 29 Dec 2022

Lionhead Range, 2022-12-29

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Hebgen lake observations

Date

Thu, 12/29/2022 - 16:55

Activity

Skiing

Climbed up to the ridgeline above Hebgen lake and dug on a SE aspect at ~8800 ft. HS 112 cm. Found around 8 inches of new snow at upper elevations and both of the weak layers we’ve been concern about. ECTN11 x 2 on the facets just beneath the new snow and no results on the lower facets. No signs of instability observed throughout the day. Not quite enough of a slab here above the upper facets, but definitely wouldn’t trust them in places with a wind load or more new snow.

Region

Lionhead Range

Location (from list)

Hebgen Lake

Observer Name

Ian Hoyer

Natural avalanche below Saddle Peak

Saddle Peak

Bridger Range

12/27/2022

Code

HS-N-R2-D2-O

Elevation

7500

Aspect

Latitude

45.79670

Longitude

-110.92700

Notes

On 12/28/2022 from the lower south boundary of Bridger Bowl, ski patrol saw an old avalanche crown and debris on steep rolling terrain below the large cliffs on Saddle Peak. Appeared to be 1-2 days old, 2 feet deep and 60 feet wide, N-R2-D2-O

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 Natural avalanche below Saddle Peak

Slab Thickness

24.0 inches

Vertical Fall

100ft

Slab Width

60.00ft

Images

Avalanche crown in runout zone below Saddle Peak

Snow Observation Source

Natural avalanche below Saddle Peak

Slab Thickness units

inches

Single / Multiple / Red Flag

Single Avalanche

Advisory Year

22-23

Read more about Avalanche crown in runout zone below Saddle Peak

Avalanche Details: Natural avalanche below Saddle Peak
Forecast link: GNFAC Avalanche Forecast for Fri Dec 30, 2022 GNFAC Avalanche Forecast for Sat Dec 31, 2022

Bridger Range, 2022-12-29

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Natural avalanche below Saddle Peak

Date

Tue, 12/27/2022 - 09:35

Region

Bridger Range

Location (from list)

Saddle Peak

Observer Name

Alex Marienthal

Explosive triggered deep slab at Big Sky

Big Sky Resort

Northern Madison

12/28/2022

Code

HS-AEc-R4-D3.5-O

Elevation

9800

Aspect

Latitude

45.27260

Longitude

-111.44700

Notes

From BSSP: "The avalanche factory that is The Wave did indeed go into production today. A 2lb. shot in skier’s right Castro’s Shoulder initiated an impressive deep slab avalanche that took out Castro’s Shoulder through Wave South above Vuarnet Cliffs. The secondary start zones under these paths- Castro’s Beard (south half) and Mike’s Rodeo- also avalanched away.

The bed surface appears to be the top of the original big storm in October that forms the base of the snowpack on Lone Mountain. There is a melt/freeze crust at the top of that layer, with
small grained (mostly) facets on top of the crust, with the rest of the season’s snowpack sitting on that weak
interface.

This [wide] propagation may be the result of the surface wind slab formed in the past few days finally tying the paths together enough to allow for such propagation.

The numbers are impressive- estimated crown length of 1,100 ft., crown depth of 3-4’, vertical run
of 1000 ft., and linear run of 2000 ft. We classified the slide as HS, AE (2lb.), R4/D3.5, O/G. Unfortunately,
conditions rendered good photos difficult. All the paths that avalanched have been shot repeatedly, almost
daily, all season long...."

Number of slides

Number caught

Number buried

Avalanche Type

Hard slab avalanche

Trigger

An explosive thrown or placed on or under the snow surface by hand

Trigger Modifier

c-A controlled or intentional release by the indicated trigger

R size

D size

3.5

Bed Surface

O - Old snow

Problem Type

Persistent Weak Layer

Read more about Explosive triggered deep slab at Big Sky

Slab Thickness

42.0 inches

Vertical Fall

1000ft

Slab Width

1100.00ft

Weak Layer Grain type

Faceted Crystals

Images

Explosive triggered very large deep slab at Big Sky

Slab Thickness units

inches

Single / Multiple / Red Flag

Single Avalanche

Advisory Year

22-23

Subscribe to 22-23

22-23

Cooke City Weekly Update - 30 Dec 2022

snowmobile triggered avalanche Frog Pond Basin

GNFAC Avalanche Forecast for Fri Dec 30, 2022

Upcoming Avalanche Education and Events

Weather and Avalanche Log for Fri Dec 30, 2022

Hebgen lake observations

Natural avalanche below Saddle Peak

Natural avalanche below Saddle Peak

Explosive triggered deep slab at Big Sky