22-23

Wind slabs on Saddle Peak

Date

Sat, 01/21/2023 - 11:10

Activity

Skiing

We skied down the "skyline" ridge of Saddle Peak. Recent strong winds drifted snow into small 4" soft slabs near the ridgelines, and there were a variety of new and old hard slabs and scoured surfaces throughout all elevations on the descent. We dug a pit around 9,000' and had an ECTP14 6-10" deep below a very hard slab sitting on sugary facets. We guess this is what the snowboarder triggered avalanche on Wednesday failed on, but that is just a guess. Due to the weak facets some of these hard slabs might be unstable for a few more days. Snow depth was 150-210cm where we dug. There is weak snow near the bottom of the snowpack that we need to remember for when there is heavier loading from snow and wind, but it seems unlikely it will cause an avalanche right now with little recent snowfall.

Region

Bridger Range

Location (from list)

Saddle Peak

Observer Name

Alex Marienthal

Wind slabs on Saddle Peak - 21 Jan 2023

Read more about Wind slabs on Saddle Peak - 21 Jan 2023

GNFAC Avalanche Forecast for Sat Jan 21, 2023

Snowpack and Avalanche Discussion

A weak layer of surface hoar buried 1-2 feet deep makes it possible for a person to trigger avalanches in the mountains around Big Sky, West Yellowstone and Cooke City. Both natural and human triggered avalanches broke on this layer earlier this week (<a href="https://www.mtavalanche.com/node/27717"><span… top details and photo</a>, <a href="https://www.mtavalanche.com/node/27740"><span… details and photos</a>, <a href="https://www.mtavalanche.com/images/23/natural-avalanche-muddy-creek-hea… Ridge photo</a>, <a href="https://www.mtavalanche.com/node/27682"><span… City photo</a>). This layer is not on every slope, and on slopes where it is buried it isn’t breaking in every stability test which makes assessment tricky (<a href="https://www.youtube.com/watch?v=jmXIADy8rl0&list=PLXu5151nmAvTi1DBS… City video</a>, <a href="https://www.youtube.com/watch?v=ibAh34muOQc&list=PLXu5151nmAvTi1DBS… video</a>). You can dig to look for and test this layer, or keep things simple and avoid steep slopes entirely (<a href="https://youtu.be/TV7IXE41Skg">… Lake video</a>).

An additional concern is where recent moderate wind has drifted snow into thicker slabs. These drifts alone can be dangerous and avalanche on steep slopes, and could cause an avalanche to break deeper and wider on buried surface hoar. Be extra cautious of wind-loaded slopes. Look for and avoid rounded pillows of snow and slopes below cornices. Avalanches breaking on weak layers near the ground are unlikely, but a person might be able to trigger a slide from a shallower area in the snowpack where these layers are easier to affect. Today avalanches are possible to trigger and danger is MODERATE.

In the Bridger Range and Hyalite moderate to strong wind over the last 24 hours drifted recent snow into shallow slabs that could avalanche under the weight of a person. In the Bridger Range wind is gusting strong at mid-elevations and may be forming drifts well below the ridgelines and in less common areas. Fresh wind slabs will be most hazardous where they could knock you off a cliff, down steep terrain, through rocks, or into trees. Watch for cracks in the snow around your skis or sled as a sign fresh drifts are unstable, and steer clear of round deposits of snow, especially where being caught in an avalanche would have high consequences. Drifts of snow that formed earlier this week are less likely to break, but a couple might remain unstable (<a href="https://www.mtavalanche.com/node/27716"><span… triggered slide on Saddle Peak</a>, <a href="https://www.mtavalanche.com/images/23/shallow-avalanche-argentina-bowl"… running slide in Argentina Bowl</a>).

Although we have not seen avalanches breaking on weak layers near the ground in the mountains around Bozeman, plenty of weak snow exists. On Wednesday, skiers on Ross Peak decided not to ski a steep slope after getting unstable test results breaking near the ground (<a href="https://www.mtavalanche.com/node/27697"><span…;). An unstable slab might rest above weak snow in an isolated area or two. Before fully committing to ski or ride steep slopes, dig down to look for and assess potential weak layers. Today’s strong wind makes avalanches possible and avalanche danger is MODERATE on wind-loaded slopes. Otherwise, the snowpack is generally stable and danger is LOW on all other slopes.

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

A weak layer of surface hoar buried 1-2 feet deep makes it possible for a person to trigger avalanches. You can dig to look for and test this layer, or keep things simple and avoid steep slopes entirely. Be extra cautious of wind-loaded slopes. Look for and avoid rounded pillows of snow and slopes below cornices. Avalanches breaking on weak layers near the ground are unlikely, but a person might be able to trigger a slide from a shallower area in the snowpack where these layers are easier to affect.

Read more about GNFAC Avalanche Forecast for Sat Jan 21, 2023

Upcoming Avalanche Education and Events

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

Weather and Avalanche Log for Sat Jan 21, 2023

Read more about Weather and Avalanche Log for Sat Jan 21, 2023

Bottomless

Date

Thu, 01/19/2023 - 12:00

Activity

Snowbiking

We were in the Beaverhead Mountains, mainly below Italian and Scott Peaks. We found various weak layers towards the top of the snowpack in places and in other places, completely bottomless pow approx 3+' deep. The weak layer areas the top 2" was breaking and sliding right around that 30 degree mark. We used Fatmap app to plan our route to the summit and worked our way around most 25-30 degree angles. Once we pushed that 30 degree angle that top 2" would release. In this area we observed the top 2" was hard like 1F or P hard, 4-5" of Fist or 4F, then another layer of 2" of P, and facets for about 20/30" to the ground. In the wind blown areas the top was almost solid, very hard and icy.

Not good riding, but we did it.

Region

Out of Advisory Area

Observer Name

Italian/Scott Peak

Cooke City Weekly Update - 20 Jan 2023

Read more about Cooke City Weekly Update - 20 Jan 2023

GNFAC Avalanche Forecast for Fri Jan 20, 2023

Snowpack and Avalanche Discussion

Snow that fell over the last week has drifted into slabs that you can trigger today. Watch out for slopes with  slabs of drifted snow more than a few inches deep that haven’t yet bonded (or places where there is any slab at all on slopes where just getting knocked off your feet would have big consequences). Wednesday’s snowboarder triggered slide on Saddle Peak illustrates this concern (<a href="https://youtu.be/w9COKhySd8o">…;), as does a long running slide in Argentina Bowl (<a href="https://www.mtavalanche.com/images/23/shallow-avalanche-argentina-bowl"…;). This issue isn’t present everywhere, there are many places where these slabs are very thin or they have had time to bond and stabilize. Cracks shooting out in front of your skis or sled indicate you’ve found a drift that remains unstable and should immediately retreat off steep slopes.

In the mountains around Big Sky, West Yellowstone and Cooke City there is a weak layer of surface hoar buried 1-2 ft deep. There have been both natural and human triggered avalanches on this layer this past week (<a href="https://www.mtavalanche.com/node/27717"><span… top details and photo</a>, <a href="https://www.mtavalanche.com/node/27740"><span… details and photos</a>, <a href="https://www.mtavalanche.com/images/23/natural-avalanche-muddy-creek-hea… Ridge photo</a>, <a href="https://www.mtavalanche.com/node/27682"><span… City photo</a>). As Alex found yesterday near Cooke City, this layer is not on every slope and even on slopes where it’s present, it isn’t breaking in every stability test (<a href="https://www.youtube.com/watch?v=jmXIADy8rl0&list=PLXu5151nmAvTi1DBS… City video</a>). This makes it hard to assess (<a href="https://www.youtube.com/watch?v=ibAh34muOQc&list=PLXu5151nmAvTi1DBS… video</a>). Your options are to dig, carefully test this layer and accept a certain degree of uncertainty, or keep things simple by avoiding steep slopes entirely (<a href="https://youtu.be/TV7IXE41Skg">… Lake video</a>). We haven’t had reports of this layer buried in the mountains around Bozeman.

Weak layers near the ground still deserve mention and a degree of consideration. It’s been a couple weeks since the last avalanche broke on these layers, but it’s not out of the realm of possibility you could trigger a slide from a thin spot that propagates deeply and results in a large slide. On Wednesday, skiers on Ross Peak made the wise call to back off a steep slope after getting unstable test results breaking near ground (<a href="https://www.mtavalanche.com/node/27697"><span…;). Remain wary of these layers.

With weak layers throughout the snowpack and recent wind drifts, triggering avalanches remains possible. For today the avalanche danger is rated MODERATE on all slopes.

Snow that fell over the last week has drifted into slabs that you can trigger today. Watch out for slopes with slabs of drifted snow more than a few inches deep that haven’t yet bonded. In the mountains around Big Sky, West Yellowstone and Cooke City there is a weak layer of surface hoar buried 1-2 ft deep that has been avalanching. Dig, carefully test this layer and accept a certain degree of uncertainty, or keep things simple by avoiding steep slopes entirely.

Read more about GNFAC Avalanche Forecast for Fri Jan 20, 2023

Upcoming Avalanche Education and Events

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

Weather and Avalanche Log for Fri Jan 20, 2023

Read more about Weather and Avalanche Log for Fri Jan 20, 2023

buried surface hoar

Date

Thu, 01/19/2023 - 23:35

Activity

Snowmobiling

We are finding impressively strong snowpack. But we also have a weak layer buried about 2 feet into the snowpack that is very worrisome. It's deep enough that when triggered will be deadly, consider consequences and know where the persistent weak layer is before exposing your group. We have been on the snow all week and find lots of powder to play in without using slopes and connected terrain that is greater than 30 degrees.

SE aspect, 7640 ft, HS 130, PWL buried SH 83, DH 45, CTHsc@83, ECTN23@45.

This PWL is widespread, but not necessarily reactive in all areas. We did feel a collapse on this same aspect and elevation yesterday, near Sawtelle Creek so we went back to test and found some results.

Region

Island Park

Location (from list)

Centennials - Idaho

Observer Name

Bret Rasmussen

Read more about ECTP15, NE aspect, 9,200' - 19 Jan

We dug five snowpits and performed extended column tests in each on 1/19/23 near Cooke City. Four snowpits were on northeast to north facing slopes between 9,200-10,000', and one pit was on a southwest facing slope at 9,200'. In one pit on a NE aspect at 9,200' we had an ECTP 15 on the surface hoar 35 cm below the surface. In all other pits we had ECTN14-19 at the depth of the surface hoar, and no obvious feathery crystals were visible. The layers where the ECTNs broke appeared to be decomposing, preserved dendrites or maybe decomposing surface hoar. Photo: GNFAC

Forecast link: GNFAC Avalanche Forecast for Sat Jan 21, 2023

Cooke City, 2023-01-19

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