GNFAC Avalanche Forecast for Wed Dec 23, 2020
<p>Strong, swirly winds at all elevations and 4 days of snowfall spiked the avalanche danger. Over 2 feet of snow fell (2.2” <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</u></a><u> </u>- SWE) and yesterday there were many natural avalanches on wind-loaded slopes and a couple skier triggered slides, one breaking hundreds of feet wide (<a href="https://www.mtavalanche.com/node/23352"><strong><u>details</u></strong>…;). All were avalanching at the interface between the old and new snow (1-3’ deep). Ian and I are in Cooke City and saw a few of these and noted the instability in our snowpits (<a href="https://youtu.be/bHZazXX4EXM"><strong><u>video</u></strong></a>). For today, check out the 5 entries for <a href="https://www.mtavalanche.com/avalanche-activity"><strong><u>avalanche activity</u></strong></a> and look at the <a href="https://www.mtavalanche.com/photos"><strong><u>photos page</u></strong></a> to get a handle on the problem. Today is better stability than yesterday, but triggering slides is still likely on steep slopes, especially wind-loaded, and the danger is rated CONSIDERABLE. I do not expect many <em>natural </em>avalanches today, but skier and sledder triggered ones are a serious threat. Travel on at a time in avalanche runout zones and don’t let beautiful, sunny skies paint a false, rosy picture.</p>
<p>Lionhead received an inch of snow yesterday. Faceted, sugary grains of weak snow underlie the bottom 2 feet of a 3-foot snowpack. Snowfall on Sunday triggered natural avalanches and Dave and I were able to trigger 2 from low angled terrain 30’ and 75’ away (<a href="https://www.youtube.com/watch?v=u0Wqce1UvKY&list=PLXu5151nmAvQDzKmH…;, <a href="https://mtavalanche.com/images/20/remote-triggered-avalanche-2-ski-hill…;, <a href="https://mtavalanche.com/images/20/small-snowmobile-triggered-slides-cab…;)</u></strong>. The snowfall has ended, but windblown snow is adding to the instability. Cracking, collapsing (whumpfs), and recent avalanches are signs to stay clear of steep slopes. Triggering slides on wind-loaded terrain is likely and the avalanche danger is rated CONSIDERABLE on wind-loaded slopes and MODERATE on all others. </p>
<p>The Bridger, northern Gallatin and northern Madison Ranges finally got snow: 5-7” (.5-.7” SWE). This was the largest storm since the season opener on October 11. Accompanying the snow was strong westerly wind. Avalanches are likely to be triggered on wind-loaded slopes and possible on steep, non-windloaded ones. The snowpack is weak and unstable. Sugary facets at the bottom ⅔ of the snowpack will struggle to support the new windblown snow (<a href="https://mtavalanche.com/images/20/wind-slabs-triggered-bridger-patrol">…;). For today, the avalanche danger is rated CONSIDERABLE on wind-loaded slopes and MODERATE on all others. A moderate danger is not a green light, it literally means it is possible to trigger slides.</p>
<p>The southern Madison and southern Gallatin Ranges got 1-2” yesterday with strong, gusty, west wind. The snowpack has a foundation of weak, sugary facets, but without significant loading since Friday its stability is improving. Dave and Alex rode into Taylor Fork on Monday and found poor snow structure and saw avalanche debris and crowns from Friday’s storm (<a href="https://www.youtube.com/watch?v=IUb9ub26y1o"><strong><u>video</u></stro…;, </strong><a href="https://mtavalanche.com/images/20/natural-avalanche-sunlight-basin-1"><…;, </strong><a href="https://mtavalanche.com/node/23302"><strong><u>avalanche activity</u></strong></a>). Avalanches were breaking on the loose facets in the lower part of the snowpack and when snowfall resumes I expect to see more slides. Since the snowpack is weak and triggering avalanches is possible, the danger is rated MODERATE on all slopes. </p>
<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong><u>websi…;, email (<a href="mailto:mtavalanche@gmail.com"><strong><u>mtavalanche@gmail.com</u></str…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>
Upcoming Avalanche Education and Events
See our education calendar for an up to date list of all local classes. Here are a few select upcoming events and opportunities to check out:
Natural and Skier triggered slide, YNP
"...remotely triggered slide in [YNP] today...Triggered it from about 40' away, on lower angled terrain. Adjacent profile...(HS 137, ECTV @93, on 2mm facets). It was on a wind protected, north aspect, around 8,800'. The crown was about 45cms deep, and 25' wide."
Forecast link: GNFAC Avalanche Forecast for Wed Dec 23, 2020
Near lower meadows off Republic, Hunter's Knob, E aspect ~8,900', avg 1' crown depth. Photo: G. Antonioli
Hyalite Canyon
My partner and I did not skin all the way out to Mt Blackmore, instead we kept it very mellow and stuck to the ridge line east of Blackmore Creek between the hidden lake and Hyalite reservoir. The reason we kept to mellow terrain is because there is close to no snow out in this area. The snow throughout the day will certainly help out in future tours, we saw the flakes falling from the sky for the entirety of our 2.5 hours out in the woods! Stellar dendrites all over the place! Overall, in the dense forested areas there was minimal snow coverage and a whole lot of exposed rocks and logs, not even enough snow to slide. The isolated areas where there was a clearing of trees the snow was considerably deeper, sometimes up to the middle of our calves.
The new snow we saw ranged from 9-10cm in open areas to 4cm in sheltered areas. Underneath the new snow was a crust layer from the last storm that was easily punched through to the basal facet layer. One pit was dug on a NE aspect at 7200' in sheltered trees, total snow depth was 30cm, with 9cm of fist soft new snow sitting on top of a 1cm 1F crust, and 20cm of 1.5mm-2.5mm facets going to the ground. One test resulted in ETCN11 with the failure occurring on the old crust layer. The bonding happening at that crust layer was looking pretty good as the early day snow was denser and had a higher water content. As the day went on the snow became lighter and less dense. Wind held steady all day at a constant rate of 10-15mph with gusts up to 20-25mph coming in from the west/southwest. We didn't end up skiing anything because of conditions, instead we skinned out along the hiking trails, a day in the woods is better than one at home. Hope this helps guys, thanks for all the work you do trying to keep everyone safe. Pray for snow!