22-23

Natural avalanches on Republic Mtn

Republic Mountain
Cooke City
Code
SS-N-R2-D2
Elevation
9000
Aspect
N
Latitude
45.00030
Longitude
-109.95400
Notes

GNFAC forecasters watched a natural avalanche come down from Republic Mountain from the motel door in Cooke City at 8 am on 12/21/22. Couldn't see details of the slide other than the debris running over the cliffs and powder cloud in the trees below. Likely involved new and windlbown snow, but that is pure speculation. 

A local guide reported watching several other natural avalanches running off Republic Mountain as he drove into Cooke City around 7:30 am. 

Number of slides
3
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
2
D size
2
Snow Observation Source
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

We watched a natural avalanche come down from Republic Mountain from the motel door in Cooke City at 8 am on 12/21/22. Couldn't see details of the slide other than the debris running over the cliffs and powder cloud in the trees below. Photo: GNFAC.

Cooke City, 2022-12-21

Cooke City Avalanche Conditions

Date
Activity
Skiing
Snowmobiling

Our day started with Ian watching a natural avalanche coming down from Republic Mountain from the motel door. That, combined with nearly 2 feet of snow and strong winds meant our plan was to avoid avalanche terrain entirely today. The snow wrapped up as we headed out for the morning and the visibility improved. The wind did not calm with the end of the snowstorm, and there was snow blowing out of the trees and large plumes sweeping across the hillsides. 

We did some out-and-back rides to Daisy Pass and the cabins at the bottom of the Rasta Chutes. We skied up west Henderson and to Marty’s slide. We had one collapse with shooting cracks at the new/ old snow interface while skinning up. There was a hardness change between the wind-drifted snow and the underlying powder that was detectable with skis and pole probing.

We rode on toward Daisy Pass as the temperature plummeted. Ian discovered that drifts up to 4 feet deep exist near the top of Daisy as he got stuck deeply a couple of times in the same drift. At the cabins below Lulu, we spotted the remnants of a small natural avalanche (probably failed last night) on Scotch Bonnett immediately to the north of the Rasta Chutes.

We were confident that human-triggered avalanches were likely today. They would be larger on wind-loaded slopes but dangerous to people in all steep terrain. 

Region
Cooke City
Location (from list)
COOKE CITY
Observer Name
Dave Zinn

ECTP17 Skinny Maid- Maid of the Midst

Date
Activity
Skiing

ECTP17 below wind slab on weak facets approximately 3/4mm in size. Propagation about 80cm below surface. 

Region
Northern Gallatin
Location (from list)
Maid of the Mist
Observer Name
Logan Racz and Peter Moreno

GNFAC Avalanche Forecast for Wed Dec 21, 2022

Snowpack and Avalanche Discussion

<p><span><span><span><span><span><span>Cooke City is getting hammered by snow and wind. In the last 48 hours 20” of snow fell (1.2” </span></span></span></span></span></span><a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/null/?cid=nrcseprd1314… water equivalent</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>, SWE) and SW wind gusting to 47 mph. Triggering avalanches is likely today. Any avalanche is bad news and triggering a slide deep in the snowpack is even worse. Ian and Dave are in Cooke City, and yesterday they were skeptical about getting onto steep terrain (</span></span></span></span></span></span><a href="https://youtu.be/B1BjS3G4ZWA"><span><span><span><strong><span><u><span>…;), and today they must be downright worried. Besides new snow avalanche danger they found weak, faceted snow buried 4-5 feet deep that could be triggered if a skier or rider hit a thin area of the slope. We recommend staying out of avalanche terrain as the danger is rated CONSIDERABLE. </span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>In the last 24 hours the Lionhead area picked up 10” of snow (.4-.5” SWE). Wind is strong and drifting snow. Yesterday, I skied above Hebgen Lake and found a poor snowpack structure which is similar to many slopes in our forecast area (</span></span></span></span></span></span><a href="https://youtu.be/RNMts6wt0JQ"><span><span><span><strong><span><u><span>…;). Weak, faceted snow is underneath thicker slabs, a real-world jenga tower. Today’s snow and wind-drifting will make it likely to trigger avalanches. Stay clear of drifts and look for signs of instability like whumpfing (collapsing) as you ride or ski, or shooting cracks, both telltale signs that you are very close to triggering a slide. For today, the avalanche danger is rated CONSIDERABLE on all slopes.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>At 6 a.m. the Bridger Range had 5” of snow, 3” around Big Sky and 1” in Hyalite. Wind is SW-W at 30-50+ mph. Yesterday a skier noticed a shallow wind-slab avalanche in Beehive Basin (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/27278"><span><span><span><strong><span…;) from recent wind-loading. Another concern is a weak layer of faceted snow in the bottom half of the snowpack. Dave and I were in Beehive/Bear Basins on Sunday and agreed that although the facets are widespread, their instability is not.&nbsp; However, an unlucky person could trigger a slide on these facets. Others reached a similar conclusion on Divide Peak on Monday (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/27263"><span><span><span><strong><span…;), as well as Ian and Alex in the northern Bridger Range on Saturday (</span></span></span></span></span></span><a href="https://youtu.be/DbeAdSSJUqM"><span><span><span><strong><span><u><span>…;). New snow and wind will create dangerous conditions, especially on slopes that are wind-loaded. Look for signs of instability and dig, test and assess the snowpack. Slopes that were stable yesterday might not be today. For today, the avalanche danger is rated CONSIDERABLE on wind-loaded slopes and MODERATE on all others.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>If you get out, 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).&nbsp;</span></span></span></span></span></span><span><span><span><span><span><span>&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>In the last 24 hours 4” of snow has fallen. Wind is also strong and drifting snow.&nbsp; Weak, faceted snow is underneath thicker slabs and wind-drifting adds weight on top of the weak snow. Triggering avalanches on these slopes is likely. Stay clear of thicker drifts and tune in to signs of instability like whumpfing (collapsing) as you ride or ski, or shooting cracks, both telltale signs that you can trigger a slide.</span></span></span></span></span></span></p>

Upcoming Avalanche Education and Events

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

We took the sled up track around the north side of the knob and below the avy debris from the slide triggered a last week. Only sign of avalanche activity (other then the obvious one) was a small wind slab release on a south facing slope near the top of the pass. Marked on the map below. Photo attached is of the previous slide but the wind slab release would be where the red X is if the photo continued. Looked to be 30ft across, ran for 15-20ft and about 6inches deep. 

Cooke City, 2022-12-21