23-24

Bridger ridge wind

Date

Good morning! Not a snow observation but weather, I’m thinking that the anemometer on the ridge is rimed up and frozen given the numbers over the last 12 hours or so. Someone will have to climb up and free it this morning if it doesn’t break loose by itself. 

Region
Bridger Range
Location (from list)
Bridger Bowl
Observer Name
Pat Hinz

Natural Avalanche North of Cooke City

Cooke City
Code
SS-N-R2-D1.5
Elevation
8900
Aspect
SE
Latitude
44.98550
Longitude
-109.94100
Notes

A skier traveling north of Cooke City saw a recent natural avalanche, this likely happened earlier in the week and was noted as "relatively fresh". 

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
2
D size
1.5
Problem Type
Persistent Weak Layer
Snow Observation Source
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Cooke City Dec. 23

Date

From email: "Continued, widespread collapsing today.  About 10 good ones, and that was with very minimal trailbreaking/ about 700' vert.

No new avalanche activity to report today.  But I did note a relatively fresh avalanche yesterday (12/22) north of Cooke.  It was on a SE aspect, about 8900'. Widespread propagation there.  

Widespread collapsing yesterday.  Approx 20 significant collapses.  Many shaking trees 50'+ away."

Region
Cooke City
Observer Name
Beau Fredlund

Still weak in Island Park

Date
Activity
Skiing
Snowmobiling

We snowmobiled up to 9,000' on Sawtelle peak, then skied to dig a couple pits. Our first pit was on an East aspect on a heavily wind loaded slope. The HS was 130cm (or 4.2 feet). There was 8" of new snow equal to 0.85" SWE, sitting over old consolidated snow that made up a slab over soft, weak facets about 50cm off the ground. We had ECTP24 x2 break on the old weak snow. Our second put was on a SW aspect and had an HS of 90cm (almost 3 feet). We got an ECTP19 here breaking on the same layer of very soft, weak facets. Wind was moderate out of the west-northwest with temps in the teens F. The new snow combined with the poor snow structure will increase avalanche danger this weekend. Video attached. 

Region
Island Park
Location (from list)
Sawtelle Peak
Observer Name
Alex Marienthal

Poor structure and tests continue in the park!

Date
Activity
Skiing

Hello again from the Yellowstone Fx team! Just wanted to keep sharing some info with this poor structure. ECTP9 on a SW aspect at 8,800’ this time farther South around the East entrance. Tracking some surface hoar and radiation recrystallization as it gets buried with this system. Yay new snow. 
 

Question: we’re seeing like pencil hardness depth hoar/melt forms at the base in some places. I’ve just not use to see depth hoar that’s this hard and melted together. Curious what you would call it. 

Enjoy the Holiday Weekend!

Location (from list)
Yellowstone Park NE
Observer Name
Jacob Peterson

GNFAC Avalanche Forecast for Sat Dec 23, 2023

Snowpack and Avalanche Discussion

<p><span><span><span><span><span><span>New snow falling on a weak snowpack has pushed it to its breaking point. A few inches of new snow may not seem like a big deal, but with such a weak snowpack it is. Human triggered avalanches are likely.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Avalanche can be triggered on weak layers throughout the thin snowpack. The snow that fell during October and November became extremely weak and faceted before being capped by a slab of snow that fell in early December. Over the last couple weeks, that more recent snow has also weakened and faceted and weak feathers of surface hoar have grown on top of it all across the region (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/23/big-surface-hoar"><span><span><sp…;). With strong winds building deeper drifts it doesn’t really matter where the slide breaks, it will be deep enough to be dangerous.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Today is a day to avoid steep slopes and give them a wide berth as you pass beneath them, because triggering a slide from below is a real concern. Natural avalanches may also break by themselves, without any additional loading from a person.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>The avalanche danger is CONSIDERABLE in the mountains around Island Park, West Yellowstone, and Big Sky.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>The mountains near Bozeman and Cooke City have the same weak snowpack, but less new snow. A trace to an inch overnight and an inch or two during the day isn’t quite enough to make a change in the danger. Stay heads up for changing conditions and think carefully before entering avalanche terrain. Triggering a dangerous avalanche is still a real possibility. Do not underestimate how weak the snowpack is (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=XjNQ_Hu27Eo"><span><span><span><strong>… CIty video</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). Choosing to avoid steep slopes today is a reasonable decision.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>If you do plan to enter avalanche terrain, watch for signs of instability (cracking, collapsing, or recent avalanches) and if you see them, back off. Dig a snowpit to look for less obvious signs of instability. And carefully consider the consequences of triggering a slide on any given slope.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>The avalanche danger is MODERATE in the Bridger Range, northern Gallatin Range, and mountains around Cooke City.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>The only thing keeping the danger from spiking in these areas is that there is less new snow - if it snows more than expected, the avalanche danger will quickly rise to CONSIDERABLE.</span></span></span></span></span></span></p>

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