24-25

Fresh reactive wind slabs

Date
Activity
Skiing

We rode from Battle Ridge and skied up the east face of The Throne to look at the stability of the recent new snow.

There was 6" of low density snow from yesterday. Winds were stronger than expected, from the north at the top of the Throne, and increased through the morning.

We found fresh drifts that were reactive, cracking easily and 5-10' wide out from our skis, on south and east facing slopes around 8000-8300'.

The new snow was low density and sluffed easily on steep shady northerlies. On steep slopes facing the sun (south and east, and probably west) the new snow sat on a crust and became moist as the sun warmed it up and started to slide under skis. We saw a couple very small natural loose snow slides below rock outcrops on south facing slopes. Air temperatures were well below freezing, especially with wind chill, but the sun quickly warmed the recent new snow.

It is spring, in addition to assessing for unstable drifts of snow, plan for wet snow avalanche hazards to increase in likelihood throughout the day when the sun is out and temperatures are near or above freezing.

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

Cooke City

Date
Activity
Skiing
Snowmobiling

Rode to the wilderness boundary and skied a lap above Goose Lake. Dug in two places - all hard, dense, strong, deep snow

Rode above Goose Creek. Dug in two places along the very steep, north-facing slopes above the creek. Same. All hard, dense, strong, and deep snow. Facets from late January are buried about a meter deep and 1Finger+ hardness.

We were digging about 700 feet above the two persistent slab that were avalanches triggered on Feb 24th (about a week and a half ago). We didn't see any indication that that is a widespread problem. We didn't see any recent avalanches either. 

Digging down to the late-January facets was a pain in the a$%. It seems like when it's becoming a pain to dig down to a weak layer, it's usually not much of problem anymore.

Region
Cooke City
Location (from list)
Goose Creek
Observer Name
Staples

Wind loaded slide on backside of lionhead

Date
Activity
Snowmobiling

Looks like a recent naturally triggered slide towards the Idaho wilderness boundary on lionhead. 

GNFAC note: This slide occurred on Feb 28th (previous observation)

Region
Lionhead Range
Location (from list)
LIONHEAD AREA

Loose avalanches on blackmore

Date
Activity
Skiing

Multiple natural loose avalanches in the steep terrain of mt Blackmore. All originated at the base of cliffs or trees. Counted 4 prominent ones

Region
Northern Gallatin
Location (from list)
Mt Blackmore
Observer Name
Max

GNFAC Avalanche Forecast for Fri Mar 7, 2025

Snowpack and Avalanche Discussion

<p><span><span><span><strong><span><span>Wind Slab avalanches </span></span></strong></span></span></span><span><span><span><span><span><span>breaking</span></span></span></span></span></span><span><span><span><strong><span><span> </span></span></strong></span></span></span><span><span><span><span><span><span>up to 1 ft deep are the primary concern today. 5-7” of new snow fell near West Yellowstone in the last 36 hours. Near Cooke City, it only snowed 1” at the Fisher Creek SNOTEL site, but ski guides yesterday reported a little bit more new snow south of town and it snowed 10” nearby in Red Lodge, so there may be places on the fridges of our forecast area with higher snowfall totals. Winds haven’t been too strong, but they’ve been out of the east. Be heads up, as this is an atypical wind direction, so drifts may be in unusual locations. Yesterday, near Hebgen Lake, Dave got shooting cracks in the new snow on slopes with just a touch of wind effect (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34519"><span><span><span><span><span><…;). Steer around the deepest wind drifts today in steep terrain and give them a little bit more time to bond.</span></span></span></span></span></span></p>

<p><span><span><span><strong><span><span>Persistent Slab avalanches </span></span></strong></span></span></span><span><span><span><span><span><span>breaking 2-3 ft deep remain an additional concern. We haven’t seen much activity on these layers recently, but the new snow might be what it takes to wake them back up. If you do trigger a slide on these weak layers, it’ll be deeper, wider, and may break further above you - making it all around substantially more dangerous (rider triggered slides last week at </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34421"><span><span><span><span><span><…; and </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34413"><span><span><span><span><span><… Creek</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>). You can dig down to look for and test these weak layers, but it’s going to be hard to determine if a particular slope is primed to slide. If you decide to ride in steep terrain today, know that you’re accepting some risk one of these slides may break. After a sunny day today, we’ll have a much better idea if this new snow woke these weak layers back up - so a little patience today could go a long way.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>The avalanche danger is MODERATE today.</span></span></span></span></span></span></p>

<p><span><span><span><strong><span><span>Wind slab avalanches </span></span></strong></span></span></span><span><span><span><span><span><span>are also the primary concern around Bozeman, Big Sky, and Island Park. With the east winds, look for drifts in unusual places. Skiers near Island Park yesterday found 8-12” thick, touchy slabs of the new snow (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34517"><span><span><span><span><span><…;). I expect similar wind slabs to be easily triggered today as well.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>The lower snowpack in these areas is generally stable, so if you avoid wind drifts, you’re unlikely to trigger a slide today. Plan to avoid wind drifts and pay attention to the feel of the snow under your feet or snowmobile in case you stumble onto a drift by accident. Cracks shooting out in front of you indicate you’ve found an unstable drift and should retreat to low angle terrain.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Human triggered avalanches are possible and the avalanche danger is MODERATE.</span></span></span></span></span></span></p>

Upcoming Avalanche Education and Events

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Instability in the New and Wind Drifted Snow

Date
Activity
Skiing

We toured from the dam up the north ridge to Trapper. Light snow fell throughout the day, adding up to about 6". As we descended the east-facing bowl, cracks shot out from our skis on slopes with a subtle wind effect. Avalanches within the new and wind-drifted snow were likely, but the volume would have been relatively small and mostly concerning in technical terrain or in the presence of terrain traps. There was a new facet layer below the melt-freeze crust. It is TBD if it will be a problem. 

The other problem is continued concern about avalanches breaking 2-3 feet deep on weak layers formed during the January dry spell. The snowpack structure is weak in this area, similar to the slopes that most recently produced human-triggered avalanches in Cabin Creek, Tepee Basin, and Lionhead. Pole probing indicated this poor structure was widespread. Our pit at 9000' on a northeast-facing slope yielded an ECTP28 on the 4F- facet layer formed in January. Failures on these deep layers don't seem very likely, but, for now, step back from steep terrain to let the storm play out. Once the storm ends, we will reevaluate stability and proceed from there. While the actual likelihood is debatable, the consequences of getting caught in a slide breaking on these weak layers are not.

Region
Lionhead Range
Location (from list)
Hebgen Lake
Observer Name
Dave Zinn
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