19-20

Snowmobile triggered on Buck Ridge

Buck Ridge
Northern Madison
Code
SS-AMu-R2-D2-I
Elevation
9300
Aspect
N
Latitude
44.17440
Longitude
-111.38200
Notes

From obs (3/29/20): "This 44* slope failed 12” under the surface of the snow on a hard crust as we descended to help another stuck rider in a tree. Another layer exists 2” below the failed layer which persisted to follow me down the hill rupturing as fault lines as I continued rapidly down the hill after extracting the stuck rider. While the remaining slope only fractured without chasing me down the hill... "Photo: TJ Krob

On 3/30 forecasters saw two other different slides that broke a foot deep on surface hoar (photo).

Number of slides
2
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
2
D size
2
Bed Surface
I - Interface between new and old snow
Problem Type
Persistent Weak Layer
Slab Thickness
18.0 inches
Weak Layer Grain type
Surface Hoar
Images
Snowmobiler triggered on Buck Ridge
Rider triggered slide Buck Ridge
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year
19-20

From obs (3/29/20): "This 44* slope failed 12” under the surface of the snow on a hard crust as we descended to help another stuck rider in a tree. Another layer exists 2” below the failed layer which persisted to follow me down the hill rupturing as fault lines as I continued rapidly down the hill after extracting the stuck rider. While the remaining slope only fractured without chasing me down the hill... "Photo: TJ Krob

Avalanche Details: Snowmobile triggered on Buck Ridge
Forecast link: GNFAC Avalanche Forecast for Mon Mar 30, 2020
Southern Madison, 2020-03-30
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    • Cornice Fall near Fairy Lake

    Fairy Lake
    Bridger Range
    Code
    C-N-R2-D1.5
    Elevation
    9000
    Aspect
    E
    Latitude
    45.90430
    Longitude
    -110.95800
    Notes

    Skiers near Fairy Lake reported a cornice collapse in October Bowl.

    Number of slides
    1
    Number caught
    0
    Number buried
    0
    Avalanche Type
    Cornice fall
    Trigger
    Natural trigger
    R size
    2
    D size
    1.5
    Problem Type
    Cornice Fall
    Images
    Natural Cornice Fall, Fairy Lake
    Slab Thickness units
    centimeters
    Single / Multiple / Red Flag
    Single Avalanche
    Advisory Year
    19-20

    Natural cornice triggered in Maid of the Mist basin

    Maid of the Mist
    Northern Gallatin
    Code
    SS-NC-R1-D2-I
    Elevation
    10000
    Aspect
    E
    Latitude
    45.41110
    Longitude
    -110.98800
    Notes

    From obs. (3/29/20): "Significant wind started building mid morning, forming even bigger cornices and wind loading many slopes. Noticed this slide on an East/Northeast aspect at the back of the bowl above Maid of the Mist creek, possibly triggered by cornice fall but unknown. Happened between 9:45am and 11:30am today, as at 9:30am it was not there, and when we returned to the spot around 11:30am the slide was visible." Photo: CP

    Number of slides
    1
    Number caught
    0
    Number buried
    0
    Avalanche Type
    Soft slab avalanche
    Trigger
    Cornice fall
    R size
    1
    D size
    2
    Bed Surface
    I - Interface between new and old snow
    Problem Type
    Wind-Drifted Snow
    Slab Thickness
    12.0 inches
    Vertical Fall
    350ft
    Slab Width
    50.00ft
    Images
    Natural cornice triggered slide Maid of the Mist 2
    Natural cornice triggered avalanche in Hyalite
    Slab Thickness units
    inches
    Single / Multiple / Red Flag
    Single Avalanche
    Advisory Year
    19-20

    From obs. (3/29/20): "Significant wind started building mid morning, forming even bigger cornices and wind loading many slopes. Noticed this slide on an East/Northeast aspect at the back of the bowl above Maid of the Mist creek, possibly triggered by cornice fall but unknown. Happened between 9:45am and 11:30am today, as at 9:30am it was not there, and when we returned to the spot around 11:30am the slide was visible." Photo: CP

    Avalanche Details: Natural cornice triggered in Maid of the Mist basin
    Forecast link: GNFAC Avalanche Forecast for Mon Mar 30, 2020GNFAC Avalanche Forecast for Tue Mar 31, 2020
    Northern Gallatin, 2020-03-29
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    • GNFAC Avalanche Forecast for Sun Mar 29, 2020

    Snowpack and Avalanche Discussion

    <p>Three days ago several skier triggered and natural avalanches were reported (<strong><a href="https://www.mtavalanche.com/images/20/skier-triggered-slide-hyalite">ph…;, <a href="https://www.mtavalanche.com/images/20/two-natural-avalanches-beehive-ba…;, <a href="https://www.mtavalanche.com/weather/wx-avalanche-log">weather and avalanche log</a></strong>). Many of these broke below the recent snow, 1-2 feet deep on weak layers above a thick crust. Similar slides are possible to trigger today. The last couple days we received reports of unstable test scores on this layer throughout the advisory area. Doug and Dave found unstable test scores on this layer at Lionhead and Taylor Fork on Friday (<a href="https://www.youtube.com/watch?v=ZkyjbN1sWl0&amp;list=PLXu5151nmAvSbcbVf…;). Before you ride steep slopes, dig down a couple feet to assess snow stability. Regardless of test scores, today it is wise to avoid steep slopes with a slab of snow sitting on a crust.</p>

    <p>Be especially cautious where moderate wind forms fresh drifts. These drifts alone can avalanche, or they can break a couple feet deeper on buried weak layers. Stay far back from cornices along ridgelines and avoid slopes directly below cornices (<strong><a href="https://www.mtavalanche.com/images/20/huge-cornices-lionhead-ridge">pho…;). Cornices can break further back than expected, and possibly trigger large avalanches.</p>

    <p>Warmer temperatures and a little sunshine today will make wet avalanches possible. Wet loose avalanches can be triggered on steep slopes where the surface becomes wet. Wet avalanches could break deeper on the recently buried weak layers and crusts. Avoid steep slopes where the snow surface gets moist or wet, and be cautious of steep, rocky terrain above where natural wet avalanches might initiate as the day warms up.</p>

    <p>Today heightened avalanche conditions exist, avalanches are possible and danger is rated MODERATE.</p>

    <p>We plan to end daily avalanche forecasts on Sunday, April 5<sup>th</sup> and continue with general bulletins every Monday and Friday through April. We have taken down most 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 <a href="https://mtavalanche.us17.list-manage.com/track/click?u=6653a830e4819c9e…; target="_blank">observation form</a>, email us (<a href="mailto:mtavalanche@gmail.com&quot; target="_blank">mtavalanche@gmail.com</a>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

    Backcountry Skiing and Stay-at-home Order

    Please consider mellower terrain and lowering your risk to reduce potential for a needed rescue. Also, the distraction of current events may cloud our judgment which compromises our ability to safely attempt more challenging objectives.

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