22-23

GNFAC Avalanche Forecast for Wed Mar 29, 2023

Snowpack and Avalanche Discussion

The northern Gallatin Range is windier than other areas. Beginning last night gusts from the southwest are blowing 30 mph. There is 2+ feet of snow to blow around and newly formed wind slabs will be easily triggered today. Climbers need to be extra careful in gullies and skiers need to be on the lookout for any shooting cracks. On slopes not wind loaded, dig and test the top 3 feet of the snowpack to see how the new is bonding to the old surface. A few natural slides were seen that were breaking under the new snow (<a href="http://www.mtavalanche.com/node/28861">… and photos</a>).

This range has also had deep and scary avalanches from weak layers 5+ feet deep that are breaking in a random way (<a href="http://www.mtavalanche.com/node/28798">… and photo</a>). While rare, these slides are deadly. Notching back slope angles to below 30 degrees will keep you safe, yet if you decide to get into avalanche terrain only expose one person at a time.

The danger is rated CONSIDERABLE on wind-loaded slopes and MODERATE on all others.

Ridgetop wind is blowing SE-SW at moderate speed creating wind drifts that are being fed by last weekend’s powder (14-32”). These drifts could crack and avalanche under your feet or machine. Ian and I went into the Throne in the Bridger Range yesterday. Underneath the new snow we found a layer of facets that broke in our stability test that was also responsible for avalanche activity during and immediately after the storm (<a href="https://youtu.be/8gXkzoEbk6Q">…; and <a href="http://www.mtavalanche.com/node/28856">…;). Skiers also triggered slides <a href="https://www.mtavalanche.com/node/28850"><span… Big Sky Ski Resort</a> and on <a href="https://www.mtavalanche.com/node/28823"><span… Ellis</a>. It’s worth taking a few minutes to dig down 3 feet and test the stability before committing to avalanche terrain.

Complicating our stability assessment is the possibility of deep slab avalanches, most prominent in the southern ranges. Buried 3-5 feet deep is a weak layer that could break on a few, isolated slopes. Cooke City had more than a fair share of these, the most recent was last Thursday near Chimney Rock when 2 sledders were caught and 1 was badly injured (<a href="http://www.mtavalanche.com/node/28785">… and photos</a>).

Wind-loading and a recently buried weak layer are the primary avalanche concerns today. These can be navigated with awareness and investigation of the snowpack. Slopes that could produce large, deep avalanches, on the other hand, are not easily identified. However, triggering them is most likely in thinner areas of the snowpack, but those areas are not visible on the surface. This presents a quandary. Dave explains how we can stack the deck in our favor by choosing terrain that is safer in his 2-part video series from Cooke City (<a href="https://youtu.be/nJWsF4g2Rjc">… 1</a>, <a href="https://youtu.be/jrjIs789meI">… 2</a>). In essence, either avoid avalanche terrain or choose terrain lacking traps like trees and cliffs.

The avalanche danger is rated MODERATE on all slopes.

Please share avalanche, snowpack or weather observations via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

Ridgetop wind is blowing SW creating wind drifts that are being fed by last weekend’s 2 feet of powder. Wind-loading and a recently buried weak layer are the primary avalanche concerns today. These can be navigated with awareness and investigation of the snowpack. Slopes that could produce large, deep avalanches, on the other hand, are not easily identified.

Read more about GNFAC Avalanche Forecast for Wed Mar 29, 2023

Upcoming Avalanche Education and Events

Events and Education Calendar.

Natural avalanches in Hyalite

Date

Tue, 03/28/2023 - 02:25

Activity

Snowboarding

On my walk up to divide today 3/28 I noticed a few small storm slabs that broke on the west side of the main fork of hyalite off the summer trail. This area had similar storm slabs that broke back in mid February during a large storm

up in the alpine there were no avalanches to report

Region

Northern Gallatin

Location (from list)

Hyalite - main fork

Weather and Avalanche Log for Wed Mar 29, 2023

Read more about Weather and Avalanche Log for Wed Mar 29, 2023

Large Natural on Bridger Peak

Date

Tue, 03/28/2023 - 11:55

Via phone message:

A large natural avalanche occurred on the north summit of Bridger Peak yesterday (Monday, 27 March). The crown line was complex.

Region

Bridger Range

Location (from list)

Bridger Peak

Read more about Marty's Profile - 26 March 2023

Cooke City, 2023-03-28

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New snow avalanches and crusts

Date

Tue, 03/28/2023 - 11:45

Activity

Skiing

We rode into the Throne from battle ridge and skinned up the east face. We saw three new snow avalanches (previously reported) on the SE and E faces of the Throne where we parked the sleds. Surface crusts are quite variable depending on slope angle, aspect, and shading from trees. The crust was generally present and breakable on the SE and E aspects we traveled on. We dug a quick pit on at the base of the E face. ECTP16 on 1 mm facets underneath last weekends snow. We measured 50 cm (20") of new snow with 2" snow water equilavent. Dug again in the crown of one of the slides. The new snow had consolidated a bit because of a more southerly aspect (~16" deep), but there was also 2" of SWE in the crown. Slide broke on small facets above a firm crust. The slides all appear to have run mid storm or just as it was ending. One of the slides was clearly skier triggered, the others are unknown.

The presence of facets under the new snow means that it'll take longer for that new snow to stabilize.

Region

Bridger Range

Location (from list)

The Throne

Observer Name

Ian Hoyer and Doug Chabot

After a big dump, dig and test; Throne - 28 March

Read more about After a big dump, dig and test; Throne - 28 March

Whumpfing in Emigrant Gulch Southerly Aspects

Date

Mon, 03/27/2023 - 06:15

Activity

Skiing

Toured in Emigrant Gulch on 03/27/23. The area recieved much less snow during this storm compared to nearby ranges or Northern Absarokas. ~15-20cm of new snow @7000ft, ~20-25cm @9000ft. Dug at quick snowpit on SW aspect of Chico Gully @7000ft. Snow pit was 180cm deep. ECT showed no reactive layers or propagation. However, primary concerns were a sun crust 60cm down in the snowpack and weak surgery snow near the ground. Skinning up the gully we experienced multiple whoomphs in shallower areas near 8000-9000ft and turned around. Skied up to the base of Emigrant Peak SE Gully and experienced several whoomphs at 9000ft likely on the sun crust found in our snowpit. Surface snow was fully saturated at that point. Turned around and enjoyed mellow powder skiing out.

Region

Out of Advisory Area

Location (from list)

Emigrant Peak

Observer Name

Tucker Hoefler

Stability in the W Bridgers that will not last

Date

Mon, 03/27/2023 - 18:40

Activity

Skiing

On a sunset tour we headed up to grab some low hanging fruit in the W Bridgers. We were shocked to find such a deep snowpack in the plains. Skiing a meadow off the valley floor from the North Cottonwood Canyon TH, we dug a pit at an elevation of approx. 5,800ft on a west aspect. The snowpack was 85cm deep, with this weekends new snowfall making up the top 45cm, the sun had affected the top 5cm creating a thin warmer layer and then surface crust as temperatures dropped. The bottom 40cm was a melted down, 4F hardness layer of weaker snow to the ground. At the moment the new snow appeared to be bonding well to the previous snowpack but it was very visible that this bottom layer was trending towards faceting and weakness. Our test result was ECTN 14. There was no breakage into the weak snow below the new snow. We skied a beautiful 25-30 degree pitch into the setting sun.

Region

Bridger Range

Observer Name

Addison Holtzhafer

GNFAC Avalanche Forecast for Tue Mar 28, 2023

Snowpack and Avalanche Discussion

It is possible to trigger avalanches in recently wind-drifted snow and on deeply buried persistent weak layers in the mountains around Bozeman, Big Sky and West Yellowstone. The winds increased to 10-20 mph yesterday afternoon for the first time since 14-32” of snow fell this weekend, transporting snow onto slopes where avalanches are the most likely today. Increasing cloud cover will minimize wet snow danger but shift to cooler aspects if the snow surface gets wet this afternoon.

A skier outside the boundary of Big Sky Resort triggered a fresh drift of snow from 75’ away that broke an estimated 1-2’ deep and 75’ wide. He felt “lucky” to have not had the carpet ripped out from under him (<a href="https://www.mtavalanche.com/node/28850">details and photo</a>). Riders and skiers in the Bridger Range reported a natural avalanche that failed yesterday (<a href="https://www.mtavalanche.com/node/28846">details and photo</a>) and two avalanches that failed on the Throne during the storm (<a href="https://www.mtavalanche.com/node/28848">details and photo</a>). Review the <a href="https://www.mtavalanche.com/avalanche-activity">avalanche activity log</a> for information about all the recent slides, including a small avalanche that partially buried a skier or rider on Little Ellis south of Bozeman (<a href="https://www.mtavalanche.com/node/28823">photos and details</a>).

While this weekend’s avalanche activity involved new and wind-drifted snow, less than a week ago, a slide broke 8-10 ft deep in Hyalite Canyon (<a href="https://www.mtavalanche.com/node/28785">details and photos</a>). Our <a href="https://www.youtube.com/playlist?list=PLXu5151nmAvTi1DBS5B4DBCruL1ULhkt… videos</a> highlight this concern and how it affects our decision-making.

Eliminate the risk of getting caught in an avalanche by staying off and out-from-under terrain steeper than 30 degrees or reduce the chances of triggering a slide by selecting non-wind-loaded slopes and assessing for obvious instability in the upper few feet of the snowpack. The avalanche danger is MODERATE.

The primary avalanche concern around Cooke City is triggering an avalanche on deeply buried weak layers. Most recently, two riders were caught and one was seriously injured by a slide that broke 4 feet deep on Henderson Mountain last Thursday (<a href="https://www.mtavalanche.com/node/28785">details and photos</a>, <a href="https://www.facebook.com/100004284780258/videos/1424658804963632?idorva…;). Riding for the last two days in the area, we observed several snowdrifts near ridgelines that broke and avalanched. While wind-drifted snow is a concern in steep terrain, the potential for deep slab avalanches drives our decision-making. Terrain selection and avalanche avoidance is the key. In my videos from Cooke City, I discuss selecting non-wind-loaded terrain and slopes that minimize the chances of getting caught and reducing the consequences of a mistake by limiting exposure to terrain traps like gullies, trees, cliffs and rocks (<a href="https://www.youtube.com/watch?v=nJWsF4g2Rjc&lc=Ugz-FtvI57p9UyUzF3h4…; <a href="https://www.youtube.com/watch?v=jrjIs789meI">video…;).

Human-triggered avalanches are possible, and the avalanche danger is MODERATE.

Please share avalanche, snowpack or weather observations via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

Triggering an avalanche in the recent snow and wind-drifted snow is possible on steep slopes in the Centennial Mountains. Avalanches can also break several feet deep on buried weak layers. Eliminate the risk of getting caught in an avalanche by staying off and out-from-under terrain steeper than 30 degrees or reduce the chances of triggering a slide by selecting non-wind-loaded slopes and assessing the snowpack for instability before considering steep slopes.

Read more about GNFAC Avalanche Forecast for Tue Mar 28, 2023

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