21-22

"5/3/22 at approximately 4:00pm a storm slab avalanche occurred in beehive basin on a west aspect @9000 ft. This slab was 6-8” deep and propagated around 50’. No one was buried, however we aren’t sure if anyone was caught because we were not the party who triggered this avalanche. We did witness the party drop in but quick went out of sight." Photo: H. Bigos-Lowe

Northern Madison, 2022-05-04

GNFAC Avalanche Forecast for Mon May 2, 2022

Snowpack and Avalanche Discussion

<h3><strong>GENERAL SPRING SNOWPACK AND TRAVEL ADVICE</strong></h3>

<p>NEW SNOW AND WIND LOADED SLOPES</p>

<p>Spring storms are notorious<sup> </sup>for depositing heavy amounts of snow in the mountains. Even with a generally stable snowpack throughout the advisory area, heavy and rapid loads of new snow will decrease stability. The main problems to look out for are avalanches breaking within the new snow, wind slabs, and loose snow avalanches. The likelihood of triggering an avalanche spikes during and immediately after snowstorms. New snow instabilities tend to stabilize quickly, but it’s a good idea to give fresh snow a day to adjust before traveling on steep slopes. New snow instabilities can be challenging to assess, and spring storms bond to old snow differently across aspects and elevations. Conservative terrain selection is essential during and immediately following storms. Avoid wind-loaded slopes and slopes steeper than 35 degrees for 24-48 hours after new snow and wind.</p>

<p>New snow can quickly change from dry to wet on a spring day, and stability can decrease rapidly with above freezing temperatures or brief sunshine. New snow may bond well early in the morning and then easily slide later. Wet loose slides are likely during the first above freezing temperatures or sunshine after a storm. Anticipate changes in snow stability as you change aspect or elevation and over the course of the day. An early start is always an advantage. Be ready to change plans or move to safer terrain at the first signs of decreasing stability.</p>

<p>WET SNOW AVALANCHES</p>

<p>Spring and wet snow avalanches go hand-in-hand. Above freezing temperatures, rain, and/or intense sunshine cause the snow to become wet and weak, and wet avalanches become easy to trigger or release naturally. Conditions tend to become most unstable when temperatures stay above freezing for multiple days and nights in a row. Avoid steep terrain, and be aware of the potential for natural wet avalanches in steep terrain above you, if you see:</p>

<ul>
<li>Heavy rain,</li>
<li>Above freezing temperatures for more than 24 hours,</li>
<li>Natural wet avalanches,</li>
<li>Rollerballs or pinwheels indicating a moist or wet snow surface,</li>
<li>Or if you sink to your boot top in wet snow.</li>
</ul>

<p>In general, if the snow surface freezes solid overnight, the snowpack will be stable in the morning and stability will decrease through the day as snow warms up. The snow surface hardness, rate of warming, duration of sunshine, aspect and elevation determine how fast stability will decrease through the day. Be aware that sunny aspects may have a wet snow avalanche danger while shadier slopes still have a dry snow avalanche danger. Getting off of steep slopes should be considered when, or before, the above signs of instability are present. Wet snow avalanches, whether loose snow or slabs, can be powerful, destructive and very dangerous. Conservative terrain choices, starting early in the day, and careful observations can keep you safe.</p>

<p>CORNICES</p>

<p>Cornices along ridgelines are massive and can break under the weight of a person. Prolonged above freezing temperatures and rain make them weaker and possible to break naturally. They can break off suddenly and farther back than one might expect. Cornice falls can also entrain large amounts of loose snow or trigger slab avalanches. Stay far back from the edge of ridgelines and minimize exposure to slopes directly below cornices. Regardless of whether a cornice triggers a slide or not, a falling cornice is dangerous to anyone in its path.</p>

<p>DISCLAIMER</p>

<p>It does not matter if new snow falls or not, avalanches will continue to occur until the existing snowpack is mostly gone. Always assess the slope you plan to ride with diligence and safety in mind. Do not let your guard down. Travel with a partner, carry rescue gear and only expose one person at a time in avalanche terrain.</p>

<p>Have a safe and enjoyable spring and summer!</p>

<p>Doug, Alex, Ian and Dave</p>

<p>For more spring travel advice see this&nbsp;<a href="https://www.mtavalanche.com/blog/transitions-spring-snow-avalanche-prob… our GNFAC forecaster blog.</p>

<p>We will continue to share relevant avalanche and snowpack information on our website and social media when available. If you get out, please send us your observations no matter how brief. 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>

Give Big Gallatin Valley

Give Big Gallatin Valley is May 5th –6th. The Friends of the Avalanche Center are participating again this year and thank you for your support.

From obs 5/1/22: "This morning we toured south of Flathead Pass to check out the conditions. We noticed on our way up that the freezing line was ~7500 ft. The punchy and wet surface crust became quite supportive and icy at this altitude. We dug a pit at ~7900ft on a NE aspect. At this location, the overnight snow totaled only 2cm but we observed more significant wind deposition in and around the trees of about 10cm. Our shovel shear tests resulted in an easy shear at 120cm and hard shear (Q1) at 90cm.

Bridger Range, 2022-05-02

Loose Wet Avalanches at Bridger Bowl

Bridger Bowl
Bridger Range
Code
WL-N-R2-D2-I
Elevation
8000
Aspect
E
Latitude
45.81560
Longitude
-110.92300
Notes

From 4/30/22: "...there were several wet loose avalanches at Bridger today. Some with ~5cm of snow on top, maybe from yesterday or earlier in the week, and some new this morning. We watched a relatively slow moving natural size 2 come down Colter's area around 10:30. We also ski cut a size 1.5 from the skiers right of the Lower Nose (NE asp) around 9:45 which ran on the melt freeze crust from earlier this week. It moved slowly but I was surprised by how much mass it entrained. A couple other ski cuts just above had produced smaller size 1s. The debris stopped on top of an older debris pile which was significantly larger and had run significantly further. (You can kind of see the difference in the photo). There was also widespread roller balling and pinwheeling on all aspects and elevations. Note - sizes are D sizes..."

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Wet loose-snow avalanche
Trigger
Natural trigger
R size
2
D size
2
Bed Surface
I - Interface between new and old snow
Problem Type
New Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

From 4/30/22: "...there were several wet loose avalanches at Bridger today. Some with ~5cm of snow on top, maybe from yesterday or earlier in the week, and some new this morning. We watched a relatively slow moving natural size 2 come down Colter's area around 10:30. We also ski cut a size 1.5 from the skiers right of the Lower Nose (NE asp) around 9:45 which ran on the melt freeze crust from earlier this week. It moved slowly but I was surprised by how much mass it entrained. A couple other ski cuts just above had produced smaller size 1s.

Bridger Range, 2022-05-02

Wet new snow slide in Beehive

Bear Basin
Northern Madison
Code
SS-AS-R1-D1.5-I
Elevation
8900
Aspect
E
Latitude
45.34530
Longitude
-111.37500
Notes

A meadow descending into bear basin. Sun affected, new snow sliding.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
R size
1
D size
1.5
Bed Surface
I - Interface between new and old snow
Problem Type
New Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year