22-23

Weak Snowpack at Goose Creek

Date
Activity
Skiing

Today I toured up to Chestnut Ridge via Goose Creek Trail. I noticed many wind deposits on the upper ridgeline that were actively thickening from the gusty Western winds (roughly 25mph average at the ridge). I dug a quick pit at 7370' on an Eastern aspect under the ridgeline and got some very touchy results. My HS was 125cm. I got a CT4, sudden collapse, Q1, breaking within a thick layer of advanced basal facets. The slab that came off was 85cm in height and very cohesive. Between the obvious wind loading near the ridge and my test result (which, I'm sure I could have replicated based on my probing of the area), our party decided to stay completely out of avalanche terrain and ski a few runs on mellow meadows and glades nearby. Minimal new snow fell during our tour -- just broken skies and a healthy dose of wind moving through the area. Stay safe out there through this storm cycle!

Region
Northern Gallatin
Location (from list)
Goose Creek

Mt Ellis (main summit)

Date
Activity
Skiing

The winds were blowing on top of Ellis Sunday, predominant direction from the SW.  New snow approximately 12-15 cms.  Dug a hasty pit, 1 meter deep, on a east facing, 30 degree slope at approximately 7700 feet.  The slope was seeing light wind loading and the top meter showed no signs of a weak layer, just a gradual increase in density with depth.  We saw/experienced no signs of snow instability.  The skiing was good, a fun time was had by all.  

Region
Northern Gallatin
Location (from list)
Mt Ellis
Observer Name
David Combs

GNFAC Avalanche Forecast for Mon Feb 20, 2023

Snowpack and Avalanche Discussion

<p>Very dangerous avalanche conditions exist in the Bridger Range and the mountains around Cooke City. Human-triggered and natural avalanches are likely. Give avalanche terrain a wide berth, by staying off and out from under any slope steeper than 30 degrees. The Bridger Range has received over 30” of snow, equal to 3.2” of <a href="https://www.mtavalanche.com/taxonomy/term/451"><span>snow water equivalent</span></a> (SWE) since Saturday morning. The mountains near Cooke City received 14” of snow equal to 0.9” SWE, primarily in the last 24 hours. Winds gusting to 55 mph are drifting snow and adding additional load to slopes at all elevations. Avalanches within the new and wind-drifted snow will be dangerous. Slides could break on buried weak layers resulting in larger avalanches that run well into the flats below.</p>

<p>As we discussed in our video from the Throne in the Bridger Range yesterday, you don’t have to stay out of the backcountry, but you do need to stay away from all avalanche terrain (<a href="https://www.youtube.com/watch?v=ncycT237y64"><strong><span>video</span>…;

<p>The avalanche danger is HIGH on all slopes.</p>

<p>The Gallatin and Madison Ranges received 10” of snow (0.9” of SWE) closer to West Yellowstone and 17” of snow (0.8-1.3” of SWE) near Big Sky and in Hyalite Canyon. Strong winds are building unstable drifts at all elevations and aspects. Continuing snowfall will load slopes to their breaking point. Human-triggered avalanches are likely within the new and wind-drifted snow. These will be enough to capture, carry and bury skiers or riders. Larger slides breaking on weak layers buried in the upper few feet of the snowpack are possible. Cautious route-finding, careful snowpack evaluation and conservative decision-making are essential.</p>

<p>The avalanche danger is CONSIDERABLE on all slopes.</p>

<p>The Lionhead area received 7” of snow in the last 48 hours (0.6” SWE). Winds gusting to 55 mph are drifting and loading this snow onto slopes that could avalanche today. Avalanches within the drifted snow will be large enough to carry a rider or skier. Turn back from steep terrain if you observe signs of instability related to recent wind-loading, such as fresh avalanche activity, newly formed pillows of snow, or cracks shooting out from your sled or skis. Any of these signs should turn us back toward lower-angle slopes or non-wind-loaded areas. A rider-triggered slide in Airplane Bowl five days ago indicates the most likely type of avalanche today (<a href="https://www.mtavalanche.com/node/28166"><strong><span>details and photo</span></strong></a>). Deeper avalanches are unlikely but dig a quick snowpit and test for instability in the upper three feet of the snowpack before riding or skiing a steep slope.</p>

<p>The avalanche danger is MODERATE on all slopes.</p>

<p>Expect the avalanche danger to rise if snowfall today if snowfall intensifies.</p>

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

<p>The Centennial Range received 5” of snow in the last 48 hours (0.4” SWE). Winds gusting to 55 mph are drifting and loading this snow onto slopes that could avalanche today. Turn back from steep terrain if you observe signs of instability related to recent wind-loading, such as fresh avalanche activity, newly formed pillows of snow, or cracks shooting out from your sled or skis. Deeper avalanches are unlikely but dig a quick snowpit and test for instability in the upper three feet of the snowpack before riding or skiing a steep slope.</p>

Upcoming Avalanche Education and Events

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

March 3-5, Bozeman Splitfest. More info and register here.

New snow, N. Bridgers

Date
Activity
Skiing
Snowmobiling

We snowmobiled and skied near the Throne and stayed on slopes less than 30 degrees and out from below any slopes steeper than 30 degrees. At 11:00am at 7,500' we measured 14" of new snow equal to 1.2" of snow water equivalent. It was snowing one inch an hour and wind was moderate with strong gusts. Avalanches of new snow were likely on steep slopes and very likely on steep wind-loaded slopes. Conditions will get more dangerous as more new snow is expected over the next couple days. We dug a pit at 7,500' on a northeast aspect. HS was 157cm and we did not see any reactive or concerning weak layers, but the new snow and wind-drifts are enough to create large, dangerous avalanches.

Region
Bridger Range
Location (from list)
The Throne
Observer Name
Alex Marienthal

Snowmobile triggered slide, Mt. Abundance, Cooke

Date
Activity
Snowmobiling

A snowmobiler triggered a 6-10" slab on a wind-loaded slope on the south side of Mt. Abundance near Cooke City on 2/18/23. Video shared with GNFAC via Facebook and YouTube.

Region
Cooke City
Location (from list)
COOKE CITY

Snowmobiler Carried, Mount Abundance

Mt. Abundance
Cooke City
Code
SS-AMu-R2-D1.5-I
Latitude
45.07720
Longitude
-110.02100
Notes

A snowmobiler triggered an avalanche on a wind-loaded slope near Mount Abundance and was carried downhill. The sled hit a tree but the rider was not buried or injured. 

Number of slides
1
Number caught
1
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
2
D size
1.5
Bed Surface
I - Interface between new and old snow
Problem Type
Wind-Drifted Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year