22-23
From instagram: Skier triggered windslab on Scotch bonnet near Cooke City. Approximately 75 ft wide.
Forecast link: GNFAC Avalanche Forecast for Sun Apr 9, 2023
Deep Slab Activity on Jumbo Mountain
Went for a ski on Jumbo Mountain via the Lava lake parking lot....
The big surprises for the day were 3 separate deep slab avalanches since the most recent loading event (likely 4/3). Photos are attached. The first that we sighted was on the N/NE face of Jumbo. It appears to be cornice fall triggering a windslab that stepped down, photo attached.
HS-N-R2-D2-O @ around 10000ft on the N/NE face of Jumbo.
the next that we sighted was a large deep slab on the E face of the ridge just north of the true summit of Jumbo.
HS-N-R2-D2.5-O @ around 10,000ft.
The real show stopper was on the E face of Jumbo.
HS-N-R4-D3.5-O/G. Approximate crown width of 1000ft and average depth of 6-8ft. Total run of around 2000ft. A few photos attached.
other slides of note, a few D1-1.5 WL slides low in the basin SW facing. Also, an older deep slab on N facing terrain just south of Hell Roaring Lake, D2-D2.5.
Southern gallatin deep slab
I went through the area of Three Rivers Peak yesterday, and there had been a pretty nice cycle of large slides recently. One on the east face of Three Rivers broke 6-800’ wide 2-10’+ deep, and ran full track. It only had a couple inches of snow on it, so I think it ran sometime during the recent warm days. Some of the walls along the slide were over 20’ high, and I imagine the debris pile might make it through the summer.
I also observed a couple older slides on E\NE aspects that were older, but not a whole lot smaller.
Meadow Lk Lemhi Range Instability and avalanches
We road into the Meadow Lake Canyon heading up above the lake in the Lemhi Range. Witnessed very sketchy conditions low and higher elevations. Saw 4 avalanches about a week old and many shooting cracks down low and a very nasty 20" think top layer on the snowpack. In that 20" inch layer on top was approx 8" consolidated snow on a 1" think ice layer and another 8-10" of consolidated snow on many feet of faceted sugar snow. We had shooting cracks hitting the cut banks of the road, heading up to around 9,000 ft where we started running into about week old slides. Slides were size 2 to 3. Slides were noted on NE, SE, NW, facing slopes. The bigger slides were at 10,000 feet.
Snowmobile triggered wind slab
Small wind slab triggered by snowmobile. Slope was assessed by group as wind blown before climb. No one was caught. East facing slope, Storm castle Ridge.
Photo one shows trigger point where the Snowmobiler carved hard and set off the slab deeper in the snowpack
GNFAC Avalanche Forecast for Fri Apr 7, 2023
<p><span><span><span><span><span><span>Spring is finally here. Temperatures will be 5-10 degrees warmer than yesterday and sunny skies will pump a lot of heat into the snow surface. This will add to wet snow concerns and raises uncertainty for the dry snow issues we’ve been dealing with for months.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Wind slabs remain reactive and another weak layer was buried last weekend. Yesterday, a skier near Cooke City triggered a wind slab in the Rasta Chutes (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28985"><span><span><span><strong><span…;) and natural slides broke 1-3 ft deep on wind loaded slopes near Cooke City and in the Bridgers (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28986"><span><span><span><strong><span… details</span></span></u></span></strong></span></span></span></a><span><span><span><strong><span><span>, </span></span></strong></span></span></span><a href="https://www.mtavalanche.com/node/28983"><span><span><span><strong><span… Peak details</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). In the Taylor Fork, I found a thin layer of weak facets ~18” below the snow surface and got unstable test results on it (ECTP13) (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28980"><span><span><span><strong><span…;). A wetting snow surface may make it easier to trigger a slide on these layers today. Dig down to investigate the top couple feet of the snowpack for instability before riding steep slopes.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Triggering a big slide on deeper weak layers also remains possible. The last big slides broke last weekend (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28949"><span><span><span><strong><span…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28924%5C"><span><span><span><strong><s… City</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span> and the </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28900"><span><span><span><strong><span… Range</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). These layers are hard to test for so your options are really either to continue to avoid steep slopes entirely or to decide the probability is low enough that you’re willing to accept some chance of triggering a deep slide. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Wet loose avalanches in the upper snowpack will become possible as crusts break down and slopes heat up this afternoon. I don’t expect these slides to be big, but the April sun is very powerful and there is a good bit of soft snow at the surface that could be entrained, so there is substantial uncertainty. Be on alert for changing conditions because they could happen rapidly. Once there is more than a few inches of wet, sticky, surface snow, it’s definitely time to move off steep slopes.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>With a wide range of concerns and human triggered avalanches possible, the avalanche danger is rated MODERATE today.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Our last daily forecast will be this Sunday, April 9. We will issue weather and avalanche observations every Monday and Friday through April. Please share avalanche, snowpack or weather observations via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).</span></span></span></span></span></span></p>
Photo of recent, natural wind slab avalanche near Cooke City. (which likely happened last night). The avalanche is on a SE aspect around 10,000'. The crown looks to be about 1-3' deep and 75' wide.
Photo: B. Fredlund (taken 3/6/23)
Forecast link: GNFAC Avalanche Forecast for Fri Apr 7, 2023
Isolated wind slab avalanches
Photo of recent, natural wind slab avalanche near Cooke City. (which likely happened last night)
The avalanche is on a SE aspect around 10,000'. The crown looks to be about 1-3' deep and 75' wide.
The SW/ W winds were moving a good bit of snow around this morning/ today. (more so than the Lulu wx station would lead someone to believe.)
No collapsing today. Minor cracking of the fresh drifts. Fairly widespread wind effect above 9500'.
Also observed a couple of isolated wet loose avalanches today too.
Expecting more wet loose tomorrow in places..
Skier triggered wind slab near Cooke
Skier triggered windslab in the Rasta Chutes on Scotch bonnet. Approximately 75 ft wide.