22-23

Today we toured up the east ridge of Republic Mountain and descended the southeast face. We observed about 10cm of fresh snow from the night before, and winds were very calm. Our pit results did not show any propagation at the interface above the faceting snow at the base and a quick shovel shear of this layer yielded a medium Q2 shear (see photos). A series of hand pits along the southeast face showed that the interface above the faceting base took some effort to move, but it would move with some force.

Region

Cooke City

Location (from list)

Republic Mountain

Observer Name

Erich Schreier

Woody Ridge

Date

Sun, 01/15/2023 - 18:10

On Saturday we toured up Woody Ridge. We observed the buried surface at this location, a W aspect just off of the well traveled skin track on the west side of the ridge, but saw no propagation in an ECT. Cracking was observed in isolated pockets on NW aspects where wind loading was very evident.

Region

Cooke City

Location (from list)

Woody Ridge

Observer Name

Erich Schreier

Hebgen

Date

Sun, 01/15/2023 - 13:55

Activity

Skiing

I skied above Hebgen Lake today, and found excellent surface conditions with poor stability. A pit on an east-facing slope at 8650’ had a clear line visible where the buried surface hoar is, and an extended column test yielded ECTN2 10 cm down on the interface between older snow and the new snow from the past couple days, and ECTP7 on the buried surface hoar. This layer is very well preserved. We did not experience any collapsing or cracking and saw no natural slides, but another group triggered two small slides on a he surface hoar while traversing a ridgeline at the top.

Region

Lionhead Range

Location (from list)

Hebgen Lake

Observer Name

Sam Reinsel

Surface hoar slide

Hebgen Lake

Lionhead Range

1/15/2023

Code

SS-AS-R1-D1.5-O

Elevation

9000

Aspect

Latitude

44.82560

Longitude

-111.31100

Notes

From Obs: "Ski cut sent a slide that failed on the known-to-be-reactive buried surface hoar layer . Avalanche broke around 12-14” deep, 100’ wide and ran around 100 yards. It was extremely sensitive.
We had skied a similar angle/aspect slope earlier and didn’t get any reactivity. Occurred around 9000’ on NW slope.~ 32 degrees. We did this 2 times on what we thought to be low angle slopes. ended up skiing down a low angle ridge line. The buried hoar isn’t everywhere but it’s touchy when found."

Number of slides

Number caught

Number buried

Avalanche Type

Soft slab avalanche

Trigger

Skier

R size

D size

1.5

Bed Surface

O - Old snow

Problem Type

Persistent Weak Layer

Read more about Surface hoar slide

Slab Thickness

13.0 inches

Slab Width

100.00ft

Weak Layer Grain type

Surface hoar crystals

Images

Skier Triggered Avalanche near Hebgen

Snow Observation Source

Surface hoar slide

Slab Thickness units

inches

Single / Multiple / Red Flag

Single Avalanche

Advisory Year

22-23

Surface hoar slide

Date

Sun, 01/15/2023 - 13:15

Activity

Skiing

Ski cut sent a slide that failed on the known-to-be-reactive buried surface hoar layer . Avalanche broke around 12-14” deep, 100’ wide and ran around 100 yards. It was extremely sensitive.
We had skied a similar angle/aspect slope earlier and didn’t get any reactivity. Occurred around 9000’ on NW slope.~ 32 degrees. We did this 2 times on what we thought to be low angle slopes. ended up skiing down a low angle ridge line. The buried hoar isn’t everywhere but it’s touchy when found.

Region

Lionhead Range

Location (from list)

Hebgen Lake

Large Depth Hoar on Blackmore

Date

Sat, 01/14/2023 - 12:35

Activity

Snowboarding

Our goal was to ride the North Face of Mount Blackmore yesterday in hopes of north aspects still holding good snow. We noticed some cornices on the top of the line and changed our objective to another entrance onto the north face farther down the ridge from the main North face line. When we got to the top of the line we could see it was noticeably wind loaded at the top and we found very large depth hoar crystals near the bottom of the snowpack. Heaving wind loading and the large depth hoar crystals gave us pause and we hiked back up and skied down the East face. We also saw what looks like a cornice about to break off along the ridge of the North face.

Region

Northern Gallatin

Location (from list)

Mt Blackmore

Observer Name

Connor Culver

GNFAC Avalanche Forecast for Sun Jan 15, 2023

Snowpack and Avalanche Discussion

New snow that fell over the past week was blown into fresh drifts by moderate to strong south-southwest wind the last couple days. These drifts can break and avalanche under the weight of a person on steep slopes. Yesterday near Cooke City skiers observed a natural avalanche break on a wind-loaded slope (<a href="https://www.mtavalanche.com/node/27660"><span…;). Avalanches can also break deeper and wider on buried weak layers. A weak layer of feathery surface hoar buried about a foot deep causes the greatest concern. We have found it from Big Sky to West Yellowstone and near Cooke City, even on wind affected slopes where surface hoar usually gets destroyed before being buried (<a href="https://www.youtube.com/watch?v=hk_6xgHgTCo">… ridge</a>, <a href="https://youtu.be/1mFc__nNwIk">…;, <a href="https://youtu.be/ECi646U0Rtg">… Fork</a>, <a href="https://youtu.be/iBS_5itbX_U">… City</a>). Before riding steep slopes, dig down to look for and test this layer, and avoid pillows of recently drifted snow.

There is also weak snow in the middle and lower half of the snowpack. Avalanches breaking on these layers are more likely on slopes that have shallow spots where a person can more easily affect the weak layer and trigger a large avalanche. These deeper weak layers are difficult to assess with a stability test, so your best bet is to choose more conservative terrain. Large avalanches are possible and the danger is rated MODERATE.

In the Bridger and Northern Gallatin Ranges, triggering a large avalanche is unlikely. Over the last week these mountains received minimal new snow, and today’s light wind will not create fresh drifts. I skied in Hyalite yesterday and noticed strong winds were no longer transporting snow because previous snow was already drifted or hardened by wind and sun (<a href="https://www.youtube.com/watch?v=UhWH5MvlW84&list=PLXu5151nmAvTi1DBS…;). Buried weak layers are present in the snowpack, but the snowpack has had time to stabilize without additional weight from new snow and wind-loading. Over the past week skiers reported a couple small wind slabs in Hyalite (<a href="https://www.mtavalanche.com/node/27633"><span…; <a href="https://www.mtavalanche.com/node/27648"><span…;). Similar small slides could be triggered today, and pose the greatest risk where they would sweep you off a cliff or into trees. Before traveling in avalanche terrain, assess the snowpack for instability, consider the consequences of being caught in a slide, and be diligent with safe travel protocols of exposing only one person at a time and carrying proper avalanche rescue gear. Today the avalanche danger is LOW.

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 avalanches can break in recently drifted snow or on weak layers deeper in the snowpack. The most worrisome weak layer is a surface hoar layer buried about a foot deep. Before riding steep slopes, dig down to look for and test this layer, and avoid pillows of recently drifted snow. There is also weak snow in the middle and lower half of the snowpack which is difficult to assess with a stability test, so your best bet is to choose more conservative terrain to ride.

Read more about GNFAC Avalanche Forecast for Sun Jan 15, 2023

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