GNFAC Avalanche Forecast for Mon Dec 18, 2023
<p><span><span><span><span><span><span>The snowpack has a poor structure which makes human-triggered avalanches possible. Weak, sugary facets are buried below 1-2 feet of snow that fell last week. The likelihood of triggering an avalanche is slowly decreasing, but recent avalanches and red flags tell us the possibility remains. On nine of the last ten days we received reports of avalanches or signs of an unstable snowpack, such as collapsing and whumphing (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/weather/wx-avalanche-log"><span><span><span… and avalanche log</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>).</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Yesterday a skier triggered an avalanche at Lionhead and shared a </span></span></span></span></span></span><a href="https://www.instagram.com/reel/C0-qL5ZrJcd/?id=3260228715764553501_2655…; showing they triggered it from far upslope, or remotely triggered. I was north of Cooke City yesterday and experienced collapses of the snowpack and saw a snow structure similar to what is responsible for unstable conditions throughout the forecast area (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=hugfAvGd09U&list=PLXu5151nmAvSH326z…;). Also yesterday, multiple groups of skiers reported collapsing and loud “whumphs” in Beehive Basin (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/29575"><span><span><span><strong><span…;) and the Bridger Range (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/29570"><span><span><span><strong><span…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/29582"><span><span><span><strong><span…;).</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Other notable signs of instability from the last week include: Big Sky ski patrol reported two avalanches thought to be naturally triggered during the day on Friday, and later they confirmed at least one was triggered by a mountain goat (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/29552"><span><span><span><strong><span…; </span></span></strong></span></span></span><a href="https://www.mtavalanche.com/images/23/natural-avalanches-closed-terrain…;). Collapsing and whumphing of the snowpack in nearly every region of our forecast area (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/avalanche-activity"><span><span><span><stro… activity</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). Last Friday Ian saw a couple recent natural avalanches at Lionhead (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=OhmeSvFN4hI"><span><span><span><strong>…;), and last Tuesday a skier triggered a large avalanche on Mt. Blackmore in Hyalite (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=ff4qS1aF9Fs"><span><span><span><strong>…;), both are good examples of the type of avalanche you can still trigger. See our </span></span></span></span></span></span><a href="https://www.mtavalanche.com/avalanche-activity"><span><span><span><stro… activity</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span> page for a comprehensive look at recent avalanches and red flags.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Avalanches can break wide, and can be triggered on slopes steeper than 30 degrees or from lower angle terrain connected to steep slopes. Choose terrain carefully. Consider the consequences of an avalanche if you travel on or below slopes steeper than 30 degrees, and thoughtfully evaluate the snowpack. Signs to stay off steep slopes include cracking, collapsing, recent avalanches, and poor stability test scores.</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
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
Widespread Surface Hoar
Traveled Hayden and Republic Creek last two days. Surface hoar throughout all elevations and aspects including ridge tops. Generally large crystal size.
Some settling, no whomphing observed. Old slab avalanche on west Republic Ridge nearing Republic pass. Snow pit off Woody Ridge on SE aspect towards Hayden found ~80cm snow depth at 9800’ with supportive upper snowpack (4f) above weak facets to ground. ECTP16 with propagation on this interface. Ski quality good. Southern aspects developed a thin solar crust through the wknd.
Skier triggered at Lionhead
Skier triggered avalanche at Lionhead on NNE, 8600 ft. Video of remote triggering slide on IG
Skier triggered at Lionhead
Skier triggered avalanche at Lionhead on NNE, 8600 ft. Video of remote triggering slide on IG
Riders saw large surface hoar crystals while riding outside of Island Park. Photo. B.Schleicher
Forecast link: GNFAC Avalanche Forecast for Mon Dec 18, 2023
Whumpfing in T. Meadows
Went touring with the intention of skiing the main Texas Meadow S. face. Heard numerous loud whumphs while skinning across the meadow below the face. Decided to not ski and dig a pit on a similar south-facing slope. Results were a CT15 Q2. On the way back up to Bradley's had several smaller collapses but none as large and widespread as those observed in the meadow. Plenty of large surface hoar crystals on my way in too.
Wind Loaded Slope with multiple weak layers
Rode up from Red Rock road to the backside of Two Top during an AIARE 1 course to evaluate snowpack. At point +044.622746 deg / - 111.247437 deg facing N82E at 8180 ft elevation on a 20 deg slope angle we found a wind loaded slope with 118 cm deep.
Hand hardness
From
0 - 15 cm - Fist
15-38 cm - 1 finger with rounds at .5 mm
38-40 cm - pencil melt freeze layer
40 - 50 cm - 4 finger with an ETCP - 23 was observed breaking at this layer in the snowpack
50 - 79 cm - 1 finger with rounds at .5 mm
79-80 cm - Pencil melt freeze later
80-94 cm - 4 finger a CTM - SC was observed at this layer
94 - 118 cm - 1 finger with deep facets and visible surface hoar