19-20

Many natural and skier triggered wind slabs in N. Madison

Beehive Peak
Northern Madison
Code
SS-R2-D2
Latitude
45.35390
Longitude
-111.40500
Notes

Many natural and skier triggered avalanches were reported on wind loaded slopes in the Northern Madison Range on 3/26/2020.

Dudley Creek: "Was up Dudley creek today. Northern madison. Saw 2 step down avalanches on ne aspect high elevation... One ... seemed cornice triggered within 12 hrs of our tour this morning (3/26). The 2nd avalanche is in the lower photo and was probably skier trigger intentional.... It looks like they triggered a fresh wind slab under ridge, maybe ski cut, which stepped down into some older layers"

Beehive & Middle Basins:

-Two natural wind slabs observed on west facing slopes near the ridgeline in Beehive.

-4 skier triggered slides in the new snow on wind affected slopes in Beehive and Middle (observed/triggered by multiple parties)

Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
R size
2
D size
2
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

Skier triggered wind slab near Cooke

Goose Creek
Cooke City
Code
SS-ASc-R2-D1.5-O
Latitude
45.09310
Longitude
-109.95100
Notes

Skier triggered avalanche in Goose Creek.

From obs: "Wind Loaded slope. 2ft Crown. 100ft wide. firm, crusty bed surface. The avalanche was released by a ski cut."

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
Trigger Modifier
c-A controlled or intentional release by the indicated trigger
R size
2
D size
1.5
Bed Surface
O - Old snow
Slab Thickness
24.0 inches
Vertical Fall
200ft
Slab Width
200.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Two natural avalanche in Beehive Basin. The obvious avalanche was observed by skiers mid-day. There is another crown in the shadows of an avalanche that occurred earlier in the day.

Photo: J. Caton

Northern Madison, 2020-03-27

From obs: "Later in the day we ran across what we assume to be a remotely triggered avalanche from another party in the area. There were two sets of tracks on the adjacent slope with cracks visible on the slope. The avalanche occurred on a 40* east aspect at 9250' and failed on the MFcr/FC dn 35cm. We looked at the crown profile, and the structure was very similar to what we found on souths. 35cm of F->4F PP/DF overlaying MFcr/FC. We did an ECT on the crown and it failed on isolation.

Northern Gallatin, 2020-03-27

From obs: "An avalanche was triggered by a skier on the East facing wall of Beehive Basin. The slide broke on the crust layer from last week. The crown was roughly 100' wide."

Photo: C. Samuels

Northern Madison, 2020-03-27

GNFAC Avalanche Forecast for Thu Mar 26, 2020

Snowpack and Avalanche Discussion

<p>In the last 2 days the northern mountains received 18” around Big Sky and 9-12” everywhere else measuring around 1” <u><a href="https://www.mtavalanche.com/taxonomy/term/451">snow water equivalent</a></u> (SWE). There have been avalanches in the new snow. Yesterday in the Bridger Range skiers noted small slides breaking within the new snow (<strong><a href="https://www.mtavalanche.com/images/20/thin-slabs-breaking-naturally2">p…;) and on the ice crust which underlies this week’s accumulation. Also, near Hyalite Peak, skiers saw debris from a small natural avalanche that broke 12” deep in the new snow.</p>

<p>The new snow is sitting on an ice crust on many aspects and elevations. As Dave and I discovered during our tour at Bridger Bowl on Tuesday, avalanches could be triggered on this crust (<strong><a href="https://youtu.be/S_hEBqY67-g">video</a></strong&gt;). This will become especially problematic as skies clear and strong sunshine dampens the snow and triggers many loose, wet, point release avalanches that will slide far on this hard layer. Be extra careful about triggering slides if people are below you. No matter if you are on a sled or skis avoid avalanche terrain once the new snow gets wet.</p>

<p>The avalanche danger is rated MODERATE on all slopes this morning, but will rise to CONSIDERABLE for wet avalanches by this afternoon on slopes getting direct sunshine.</p>

<p>In the southern ranges, Cooke City has gotten 15” in the last 48 hours while 8-9” fell around West Yellowstone and Taylor Fork (.6-1” SWE). An ice crust of varying thickness underlies the new snow on many slopes. Avalanches are possible on this crust, no matter if they are new snow slides, slabs from wind-loading, or wet snow. Concentrate your stability assessment on the upper 2 feet of the snowpack, crust or not, since this is where instability will be found. Dave and I made a <strong><a href="https://youtu.be/S_hEBqY67-g">video</a></strong&gt; during our tour in the Bridger Range that is also applicable to the southern mountains.</p>

<p>Skies are forecasted to be partly cloudy with mountain temperatures reaching the low 30s. This will help keep wet avalanche activity from becoming widespread. The snow will dampen with direct sunshine and skiers and sledders should be on the lookout for pinwheels in the new snow, a sign that the surface is getting wet enough to avalanche.</p>

<p>Given the new snow, underlying crusts and potential for a few wet avalanches, the danger is rated MODERATE on all slopes.</p>

<p>We will end daily avalanche forecasts on Sunday, April 5<sup>th</sup> and continue with general bulletins every Monday and Friday through April. Over the next couple of weeks, we will take down weather stations and will no longer receive observations from guides and ski patrol. We need help gathering field data. Please send us your observations no matter how brief. You can fill out an <u><a href="https://mtavalanche.us17.list-manage.com/track/click?u=6653a830e4819c9e…; target="_blank">observation form</a></u>, email us (<u><a href="mailto:mtavalanche@gmail.com&quot; target="_blank">mtavalanche@gmail.com</a></u>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

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