22-23

YNP and Cooke instability

Date
Activity
Skiing

From an email:

Many collapses. HST 15cm. NSFing on the surface. Light winds out of the E, S.

Several small wind slab pockets in steep, wind loaded areas of terrain. This photo is the largest one that released. Bison, watch out!

On my drive back from the park, I noted a few others. Surprisingly, nothing on those S slopes around Meridian went.

-Old Man Rays, released mid slope, as well as a small pocket below the cliff in sympathy. SS-N-R2-D2-I(?)

-Miller Ridge, SW aspect at about 9500’, large crown. That’s all I could see.

Region
Cooke City
Location (from list)
Yellowstone Park NE
Observer Name
Nina Hance

GNFAC Avalanche Forecast for Wed Feb 22, 2023

Snowpack and Avalanche Discussion

<p><span><span><span><span><span><span>In the Bridger Range and Cooke City snowfall stopped and the Avalanche Warning expired. </span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Since Sunday, the Bridger Range received 4 feet of snow measuring 4.3” of </span></span></span></span></span></span><a href="https://www.mtavalanche.com/taxonomy/term/451"><span><span><span><span>… water equivalent</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span> (SWE). For the most part, the snowpack held together and natural avalanche activity was minimal (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28224"><span><span><span><strong><span…’s observation and photos</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). Clear skies might reveal a large avalanche or two, but in general we are optimistic about the future. However, today we cannot discount the fact that 4” of SWE is a very large load and that large avalanches can be triggered. My partners and I dug a snowpit near the Ramp on the Brider ridge. Our stability test did not show breaks in the new snow, but these tests can be unreliable with deep layers and we are not confident in the snowpack’s stability (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28244"><span><span><span><strong><span… and observations</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). Strong east wind will strip the upper slopes and create drifts on the west side of the range which are also likely to be triggered.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>The mountains around Cooke City received about 35” of snowfall measuring 2.9” of SWE. A large avalanche on Wall Mountain was seen yesterday (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/23/natural-avalanche-wall-mountain">…;) and a skier reported triggering whumpfs outside town. On Monday, a skier watched a large natural slide release on Woody Ridge (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28236"><span><span><span><strong><span… and photo</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). Visibility has been poor and we are unsure of the extent of the avalanche cycle, but today is a day to be extra careful since it’s likely to trigger large avalanches.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Give avalanche terrain a wide berth. Slopes need a day or two to adjust to the heavy snow load. </span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>For today, the avalanche danger is rated CONSIDERABLE. </span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>The entire length of the Gallatin and Madison Ranges and the Lionhead area near West Yellowstone received 15-25” of snow with this storm (1.3-1.7 '' SWE). During the storm a skier triggered a slide near Big Sky (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/23/ski-triggered-avalanche"><span><s…;) and Dave and his partner saw a natural avalanche on Buck Ridge (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=QjdtnwcWPVs"><span><span><span><strong>…;). Snowfall stopped and wind is blowing northeast which is stripping many avalanche starting zones. Although natural avalanches are unlikely today, it is still possible to trigger slides in the new snow or on slopes getting wind-loaded. Cracking or collapsing are signs of instability and these slopes should be avoided.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>For today, the avalanche danger is rated MODERATE on all slopes.&nbsp;</span></span></span></span></span></span></p>

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

<p>&nbsp;</p>

<p><span><span><span><span><span><span>In the last few days, Island Park received almost a foot of new snow. Wind has blown this snow into drifts and avalanches are possible on all slopes. Cracking or collapsing are signs of instability and these slopes should be avoided. Always follow safe travel protocols and carry a beacon, shovel, and probe.</span></span></span></span></span></span></p>

Upcoming Avalanche Education and Events

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Climax Path, Natural Avalanche

Date
Activity
Skiing

From email, "At 12:45 p.m. I saw Climax run naturally. SS-N-R2-D2-I. The low visibility and distance made it hard to tell how deep the crown was, but based on there not being much volume of debris and it not running very far I’m guessing it was within the new snow/storm interface and didn’t step down to any buried PWL."

Region
Cooke City
Observer Name
Nina

Natural Avalanche, Wall Mountain

Date

Residents of Silver-Gate caught a glimpse of a large natural avalanche south of Silver Gate on Wall Mountain. The size is uncertain, but it knocked down a stand of trees. Two people state that they believe they heard the avalanche in the pre-dawn hours. 

Region
Cooke City
Location (from list)
Wall Mountain
Observer Name
Traute

Lots of snow, but not many avalanches

Date
Activity
Skiing

We skied along the ridge to the Ramp. At times we had good visibility and were able to glass the west side and saw no avalanche activity. Alex saw only small slides yesterday to the south of the ski area. A squall in the pre-dawn hours rapidly dropped 3" of 18% snow (.5" SWE).  Winds had died down and there was no current loading as we traversed, but by the time we exited at noon snow was falling and winds were blowing north and east as the cold front hit. We dug a pit about 4 feet deep and found the new snow was not breaking in stability tests. We were encouraged by the lack of avalanche activity and no significant cracking on wind-loads, but we were still nervous given that 4 feet of snow had just fallen. We were not confident in the stability, but that will change with time as the snowpack adjusts to the heavy burden of new snow.

Region
Bridger Range
Location (from list)
The Ramp
Observer Name
Doug Chabot

Ski Cut Triggered Avalanche near Big Sky

Northern Madison
Code
SS-ASc-R2-D2-I
Elevation
9800
Aspect
W
Notes

From IG: “Ski cut trigger. West facing. 9800ft. Big sky area.”

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
Trigger Modifier
c-A controlled or intentional release by the indicated trigger
R size
2
D size
2
Bed Surface
I - Interface between new and old snow
Problem Type
New Snow
Snow Observation Source
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year