22-23

Snowpack and Avalanche Discussion

Another 3-5” of low density new snow this morning on top of yesterday’s 5-8” and strong winds means there are substantial wind drifts that are ready to avalanche. On many slopes these drifts are sitting above weak layers in the upper snowpack. Around Big Sky and Cooke City the weak layer may surface hoar (<a href="https://www.youtube.com/watch?v=jmXIADy8rl0&list=PLXu5151nmAvTi1DBS… City video</a>, <a href="https://www.youtube.com/watch?v=jQg8gqFqn1M&list=PLXu5151nmAvTi1DBS… video</a>), while near Bozeman it is more likely to be facets (<a href="https://youtu.be/1VdaJ49vISg">… Peak video</a>, <a href="https://youtu.be/c1HCGdyzt0E">… Ellis video</a>). Don’t get sucked into the weeds - today, the specific grain type of the weak layer doesn’t matter - the important thing is that there are weak layers that are being loaded, especially where wind is building thicker drifts. Don’t mess with wind slabs today - assume that there are weak layers on every slope and that avalanches will break more easily, deeper and wider than they would in just new/wind drifted snow. A natural avalanche ran over a popular west-facing ice climb (Silken Falls) in Hyalite on Tuesday (<a href="https://www.mtavalanche.com/node/27809"><span…;) and I expect more of these slides today.

More snowfall today and continued strong winds potentially increasing and shifting directions this afternoon will make new slopes unstable throughout the day, so constantly reevaluate your terrain choices. The avalanche danger is CONSIDERABLE on wind loaded slopes and MODERATE on all other slopes.

Large avalanches are a very serious possibility today. There hasn’t been much new snow, but there has been a little and there are very weak and reactive layers of surface hoar in the upper snowpack. Yesterday, Dave saw several recent natural avalanches along Lionhead Ridge that broke 1-2 ft deep on surface hoar (<a href="https://www.mtavalanche.com/node/27817"><span… and photos</a>) and got an ECTP2 (a very unstable result) on another layer of surface hoar ~5” below the surface. These slides broke after only a couple inches of new snow fell. With a dusting of new snow overnight and a bit more on the way today, it wouldn’t be surprising to trigger similar slides today. Dig and test these weak layers before riding any steep slope and be ready to back off if necessary (<a href="https://youtu.be/AbyeCAAcpGI">… Rind video</a>). The avalanche danger is MODERATE today.

If more than a couple inches of new snow fall during the day, large avalanches will quickly become likely and the avalanche danger will rise to CONSIDERABLE.

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).

In Island Park, large avalanches are a very serious possibility today. There hasn’t been much new snow, but there has been a little and there are very weak and reactive layers of surface hoar in the upper snowpack that have recently avalanched nearby. Be wary of any steep slope, but even more so of any slope with more than a few inches of wind loading. Dig and test these weak layers before riding any steep slope and be ready to back off if necessary

Read more about GNFAC Avalanche Forecast for Thu Jan 26, 2023

KING AND QUEEN OF THE RIDGE, FEBRUARY 4TH

Do you like to hike? Do you like to ski? Then the King & Queen of the Ridge is for you. Hike, ski and raise money for the Friends of the Avalanche Center in their 2nd biggest fundraiser of the year. Join the effort to promote and support avalanche safety and awareness! Fundraising prizes for the top 5 individuals who raise over $500.

Weather and Avalanche Log for Thu Jan 26, 2023

Read more about Weather and Avalanche Log for Thu Jan 26, 2023

Natural Avalanches and Surface Hoar at Lionhead

Date

Wed, 01/25/2023 - 17:50

Activity

Snowmobiling

We rode up Denny Creek and over toward Watkins Creek, etc. We observed two recent natural avalanches that broke 1-2 feet deep, presumably on a surface hoar layer. There was a couple of inches of snow on each of these slides, so I would place them between three and five days old. The slides were R1-D1.5 in size - 75-100' wide, 1-2' deep, and 100' vertical fall.

We dug a quick pit with a snow height of 120 cm (4 feet) and found one layer of surface hoar buried 5" deep (ECTP2) and 4 Finger + facets near the ground (ECTP26). We were not concerned about natural avalanches today, but they will be a concern with a few inches of new snow or more on any slope on which the surface hoar is present (assume it is everywhere at Lionhead).

Region

Lionhead Range

Location (from list)

LIONHEAD AREA

Observer Name

David Zinn

Natural avalanches in Lionhead

Lionhead Ridge

Lionhead Range

1/22/2023

Code

SS-N-R1-D1.5-O

Latitude

44.71450

Longitude

-111.31800

Notes

Observed two recent natural avalanches on 1/25/23 that broke 1-2 feet deep, presumably on a surface hoar layer. There was a couple of inches of snow on each of these slides, so I would place them between three and five days old. The slides were R1-D1.5 in size - 75-100' wide, 1-2' deep, and 100' vertical fall. Photo: GNFAC

Number of slides

Number caught

Number buried

Avalanche Type

Soft slab avalanche

Trigger

Natural trigger

R size

D size

1.5

Bed Surface

O - Old snow

Read more about Natural avalanches in Lionhead

Slab Thickness

18.0 inches

Vertical Fall

100ft

Slab Width

100.00ft

Weak Layer Grain type

Surface Hoar

Images

Natural avalanches in Lionhead 2

Natural avalanche in Lionhead

Slab Thickness units

inches

Single / Multiple / Red Flag

Single Avalanche

Advisory Year

22-23

Read more about Natural avalanches in Lionhead 2

Avalanche Details: Natural avalanches in Lionhead
Forecast link: GNFAC Avalanche Forecast for Thu Jan 26, 2023 GNFAC Avalanche Forecast for Fri Jan 27, 2023

Lionhead Range, 2023-01-25

Access other image sizes:

Read more about Natural avalanche in Lionhead

Avalanche Details: Natural avalanches in Lionhead
Forecast link: GNFAC Avalanche Forecast for Thu Jan 26, 2023 GNFAC Avalanche Forecast for Fri Jan 27, 2023

Lionhead Range, 2023-01-25

Access other image sizes:

New snow in Hyalite

Date

Wed, 01/25/2023 - 15:10

Activity

Snowboarding

My ski partners and I toured up Flanders creek today and found 9"- 11" of new low density snow. We dug a pit at the base of the SE bowl of Flanders at 9500 ft. The snowpack was 90 cm deep, slightly shallower than what we found on Divide peak last weekend. We found that the new snow was sherring easily in hand pits and we got an ECTP 6 on this interface in our pit. The layers beneath the new snow were faceted junk but not reactive in our tests. The new snow sitting on a firm crust layer was our main concern.

Region

Northern Gallatin

Location (from list)

Flanders Creek

Observer Name

Gage

Generally stable snow in Beehive W Aspects

Date

Wed, 01/25/2023 - 12:45

Activity

Skiing

We toured into Beehive for day 2 of our AAI pro 1 avalanche course. We decided to tour up the ridge between “Going Home” and “Tyler’s Run”. We dug three pits as a group on a W aspect at 8700 feet and found generally stable results with no prolongation observed in any of the three pits. We did find a layer of buried surface hoar approximately 37cm below the surface, but evidence that the surface hoar has begun to break down, sinter, and gain strength. We found approximately 10-12in of new snow at elevations above 8,000 ft, which was more than we were expecting. Light snow continued throughout the day with 2-4 inches of accumulation by 2 PM when we returned to our car. We observed light wind transport at the ridge line, but did not find any wind affected snow on the W aspect that we toured up.

Region

Northern Madison

Location (from list)

Beehive Basin

Observer Name

Maddie Beck

GNFAC Avalanche Forecast for Wed Jan 25, 2023

Snowpack and Avalanche Discussion

Yesterday was windy in the mountains around Bozeman. Gusts of 40+ mph from the northwest blew old and new snow around. Today's wind and new snow (5-6” of 5% density, aka. powder) will continue to build drifts and create dangerous avalanche conditions. Yesterday, an ice climber reported a large natural avalanche running over a popular west-facing ice climb (Silken Falls) in Hyalite. The gully above the climb was wind-loaded. I expect to see more avalanches on wind-loaded terrain today. Gullies, open slopes near the ridgelines, or any place the snow can drift are all unstable. Weak, faceted snow, like what we found on Mount Ellis yesterday (<a href="https://youtu.be/c1HCGdyzt0E">…;) and the Bridgers on Saturday (<a href="https://youtu.be/1VdaJ49vISg">… Peak</a>) and Sunday (<a href="https://youtu.be/TV4GadWjnaA">…;) is being taxed beyond its holding power on wind-drifted slopes.

For today, the avalanche danger is rated CONSIDERABLE on wind-drifted slopes and MODERATE on those protected by the wind.

The mountains around Big Sky and Cooke City are lumped together because they have a similar weak layer and similar snowfall amounts. They each received .3” of <a href="http://snow.wyo.gov/snow-surveys/snow-water-equivalent-swe"><span… water equivalent</a> (SWE) measuring 8” of snow around Big Sky and an estimated 6” in Cooke City. On some slopes, buried 1-2 feet under the surface, is a layer of feathery surface hoar that has potential to avalanche (<a href="https://www.mtavalanche.com/node/27785"><span…;). Winds are building thick drifts and the surface hoar layer is likely to be triggered by skiers or sledders. On slopes without wind drifting, .3” of SWE is not heavy enough to spike the instability on deeper layers of sugary facets near the ground. However, slopes or gullies with wind-drifting are another story and should be avoided.

For today, the avalanche danger is rated CONSIDERABLE on wind-drifted slopes and MODERATE on all others.

The mountains south of Big Sky to West Yellowstone received 1-2” of snowfall (.1-.2” of SWE). The snowpack has 2 buried weak layers: feathery crystals of surface hoar 6” to 2 feet deep, and sugary facets near the ground. Dave was in Bacon Rind on Monday and found them both collapsing and shearing in his snowpit (<a href="https://youtu.be/AbyeCAAcpGI">…;) which caused him enough concern that he and his partner descended a less steep line than they intended. Dave and I found this layer in Lionhead last week (<a href="https://studio.youtube.com/video/ibAh34muOQc/edit"><s…;) and on Monday riders around Two Top uncovered 3 stripes of surface hoar in their snow pit and decided to stay out of avalanche terrain (<a href="https://www.mtavalanche.com/node/27785"><span…;). Dig and look for this weak layer. If you find it, avoid slopes steeper than 30-degrees (avalanche terrain). If you don’t find it, dig again, and maybe even again before committing to a slope.

Today, human-triggered avalanches are possible, and the danger is MODERATE.

In Island Park, human-triggered avalanches breaking 1-2 feet deep on a weak stripe of buried surface hoar and within recently wind-drifted snow are possible. Assess and test the upper several feet of the snowpack for instability related to surface hoar. The safe solution is to avoid slopes steeper than 30 degrees.

Read more about GNFAC Avalanche Forecast for Wed Jan 25, 2023

KING AND QUEEN OF THE RIDGE, FEBRUARY 4TH

Subscribe to 22-23