24-25

Read more about Ice gullies snowpack

Ice gullies snowpack

Photo: GNFAC

Northern Gallatin, 2024-12-12

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Good low/mid elevation stability in Hyalite above ice climbs

Date

Thu, 12/12/2024 - 11:30

Activity

Ice Climbing

Checked out the snow above Mummy 2 and the Scepter. I was surprised how little snow there was, but a lot of it likely melted off during recent warm weather which was amplified by heating of all the surrounding rocks.

The old snow surface from last weekend is faceted but not too bad, and only has 6" of snow on top. The snowpack is generally very discontinuous. Climbers can mostly walk on rocky areas with minimal snow.

My main concern is what will happen when strong south winds arrive on Saturday. Some snow may fall Sunday and south winds may continue. Fresh wind slabs will be the main concern.

**This observation is not very relevant for the snowpack in the upper bowls of Hyalite where many ski**

Region

Northern Gallatin

Location (from list)

Hyalite - main fork

Observer Name

Staples

Weather and Avalanche Log for Thu Dec 12, 2024

Read more about Weather and Avalanche Log for Thu Dec 12, 2024

Trace of snow in a few places

GNFAC Avalanche Forecast for Thu Dec 12, 2024

Snowpack and Avalanche Discussion

After fresh snow Monday followed by strong winds on Tuesday, the main avalanche problem to look for and avoid are wind slabs that are a day or two old. Seek out slopes untouched by the wind with soft powder.

Complicating the situation is that the old snow surface became faceted and weak and is <a href="https://youtu.be/EzT4DqH3wE0?feature=shared"><s… buried by new snow</a>. <a href="https://www.mtavalanche.com/node/32372"><… Cooke City</a>, Alex found a buried layer of surface hoar (see the stripe in in his snowpit wall <a href="https://www.mtavalanche.com/sites/default/files/snow_obs/2024-12/img_72… the photo</a>). There have been no reports of avalanches on this faceted snow or surface hoar which is especially notable in Hyalite where up to 15 inches of snow had fallen by Monday. For now it appears that the new snow did not create a persistent slab avalanche problem yet, but the stage has been set.

For today, human triggered avalanches remain possible and the avalanche danger is MODERATE.

Less snow fell in areas further south near West Yellowstone and Island Park (about 2-4 inches by Monday morning), but it was enough to cap the old snow surface which had become weak and faceted. Surface hoar was also buried as well as Dave describes in <a href="https://youtu.be/YblD2aRUE1M?feature=shared"><s… video</a> from Island Park.

Isolated areas with wind deposited snow may have enough to cause an avalanche; otherwise, human triggered avalanches are unlikely and the avalanche danger is LOW.

Read more about GNFAC Avalanche Forecast for Thu Dec 12, 2024

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Observations in Hyalite

Date

Wed, 12/11/2024 - 10:00

Activity

Skiing

Iv been fortunate enough to spend the past three days skiing around hyalite. On Monday, we were skiing a low angle gully a mile NE of Backmore along the ridge. We noticed new snow point and releases on most steep aspects above 40 degrees, no signs of new snow stuff stepping down. Today while on the East Fork ridge south of Palisades mountain, I covered SE-NW aspects and the new snow seemed well bonded. Solar aspects from the high pressure last week had an obvious crust layer, but new snow seemed bonded. On shadier aspects, I felt facets below new snow but no obvious signs of instability.. yet.

Region

Northern Gallatin

Location (from list)

Hyalite - East Fork

Observer Name

Tommy S

Surprisingly Stable Snow in Upper Hyalite

Date

Tue, 12/10/2024 - 05:50

Activity

Skiing

Skied up through Maid of the Mist Basin into Twin Falls Basin, attempted to boot up the Pinner but was foiled by too much snow. Very strong (almost blew one of my skis away) wind on ridge lines transporting significant amounts of snow. Despite this snow seemed very stable, small wind/storm slab not very consolidated breaking, but not propagating. Skied all sorts of aspects and all angles and saw few signs of instability. Day before friend observed 6-8ft shooting cracks when walking across >30 degree north-eastern aspects near try line, will try to get him to submit video, skied same slope and was unable to replicate a day later. Absurdly deep conditions high up in Hyalite, some of the better turns of my life, hopeful the storm bonds well with previous snow.

Region

Northern Gallatin

Location (from list)

Hyalite - main fork

Observer Name

Titan Cox

Read more about Snowpit on Mt Blackmore

Snowpit on the Mt Blackmore

Photo: GNFAC

Forecast link: GNFAC Avalanche Forecast for Wed Dec 11, 2024 GNFAC Avalanche Forecast for Thu Dec 12, 2024 GNFAC Avalanche Forecast for Fri Dec 13, 2024 GNFAC Avalanche Forecast for Sat Dec 14, 2024

Northern Gallatin, 2024-12-11

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GNFAC Avalanche Forecast for Wed Dec 11, 2024

Snowpack and Avalanche Discussion

Across the entire forecast area, there is a weak layer under Monday’s new snow, and the most likely places to trigger avalanches are where winds blew that snow into drifts and formed wind slabs.

The most snow fell in the mountains near Bozeman and Big Sky (5-12 inches snow/0.4-0.9 inches water) with closer to 15 inches of snow in upper parts of Hyalite Canyon. Strong winds definitely transported snow yesterday mostly at upper elevation ridgelines, but it was easy to find many slopes untouched by winds. In the Bridgers, winds were transporting snow at low elevations as well.

Fresh wind slabs are the primary avalanche problem. These wind slabs are likely resting on weak, faceted snow that formed on the snow surface prior to Monday’s snowfall. On sunny slopes this weak layer is just below an ice crust. Near Cooke City, <a href="https://www.mtavalanche.com/node/32372"><… found this weak layer</a> combined with a layer of buried surface hoar evident as a stripe in his snowpit wall (<a href="https://www.mtavalanche.com/sites/default/files/snow_obs/2024-12/img_72… photo</a>).

With this widespread weak layer, we are inching closer to a persistent slab avalanche problem as Ian describes in this <a href="https://youtu.be/EzT4DqH3wE0?feature=shared"><s… from Mt Blackmore</a> near Hyalite yesterday. In most areas, there just isn’t enough snow on top of the weak layer for this to be an issue yet, and in the Bridger Range this weak layer is much less developed. However, I’d be especially cautious in the Hyalite area which received so much new snow or near Cooke City which has less new snow but a notorious weak layer of buried surface hoar.

Today, the danger is CONSIDERABLE on wind-loaded slopes and MODERATE on all others

Further south in the forecast area near West Yellowstone and Island Park, there is a similar weak layer of facets and surface hoar that formed on the snow surface prior to Monday’s snowfall. Dave describes it in <a href="https://youtu.be/YblD2aRUE1M?feature=shared"><s… video</a> from Island Park. However there is only 2-4 inches of new snow on top of this weak layer which isn’t really enough to cause an avalanche.

Watch out for isolated areas that may have received a little more snow on Monday and any slope with some wind-blown snow where there may be just enough new snow for an avalanche. Overall avalanches are unlikely except in these isolated areas and the avalanche danger is LOW.