19-20

We visited the avalanche that was triggered by a snowmobiler and partially buried 2 people on January 4th. The crown was 10 feet at the deepest part. Photo: GNFAC

Avalanche Details: Three snowmobilers caught in very large slide on Buck Ridge
Forecast link: GNFAC Avalanche Forecast for Mon Jan 6, 2020GNFAC Avalanche Forecast for Tue Jan 7, 2020
Northern Madison, 2020-01-05
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    • Deep slab avalanches triggered by Big Sky patrol

    Big Sky Resort
    Northern Madison
    Code
    HS-AEc-R3-D2.5-O
    Elevation
    10000
    Aspect
    SE
    Latitude
    45.27600
    Longitude
    -111.43600
    Notes

    "We triggered 3 significant persistent slabs with explosives on the south face, all in areas that had been rapidly loaded by last night’s winds.  Castro’s shoulder, Upper Rodeo and Jailbait (HV) all succumbed to the load and failed 3-6’ deep on the ice crust 30-60 cm off the ground and showed impressive propagation.  One significant new snow slide in Lenin failed 4-5’ deep just involving snow that had been deposited since this storm began." - BSSP

    Number of slides
    3
    Number caught
    0
    Number buried
    0
    Avalanche Type
    Hard slab avalanche
    Trigger
    An explosive thrown or placed on or under the snow surface by hand
    Trigger Modifier
    c-A controlled or intentional release by the indicated trigger
    R size
    3
    D size
    2.5
    Bed Surface
    O - Old snow
    Problem Type
    Persistent Weak Layer
    Images
    Big Sky patrol triggered deep slab 2
    Big Sky patrol triggered deep persistent slab
    Slab Thickness units
    centimeters
    Single / Multiple / Red Flag
    Multiple Avalanches
    Advisory Year
    19-20

    GNFAC Avalanche Forecast for Sun Jan 5, 2020

    Snowpack and Avalanche Discussion

    <p>Yesterday on Buck Ridge near Big Sky three snowmobilers were caught in a very large avalanche that was 4-6 feet deep, 1500’ wide and broke on sugary snow at the bottom of the snowpack (<strong><a href="https://www.mtavalanche.com/images/20/snowmobile-triggered-very-large-a…;, <strong><a href="https://www.mtavalanche.com/node/21453">details</a></strong&gt;). Two of them were partially buried to their waist. Luckily all were unharmed, but this could have been a tragedy. The last two days similar large avalanches were triggered and broke naturally on sugary, persistent weak layers deep in the snowpack. These include: The close call mentioned above, a <strong><a href="https://www.mtavalanche.com/node/21427">natural slide on Saddle Peak</a></strong>, a <strong><a href="https://www.mtavalanche.com/node/21440">natural on Yellow Mountain</a></strong> near Big Sky, and deep avalanches triggered by Big Sky and Bridger Bowl ski patrols during control work (<strong><a href="https://www.mtavalanche.com/images/20/big-sky-patrol-triggered-deep-per…;, <strong><a href="https://www.mtavalanche.com/images/20/bridger-patrol-triggered-deep-sla… and photos</a></strong>).</p>

    <p>Today throughout the advisory area similar large, deadly avalanches are possible to trigger. See our <strong><a href="https://www.mtavalanche.com/photos?field_advisory_year_target_id=438&am… page</a></strong> and <strong><a href="https://www.mtavalanche.com/avalanche-activity">avalanche activity log</a></strong> for a comprehensive look at the types of slides that are possible. Today the snowpack gets a break from loading by heavy snow and strong wind, and will slowly begin to stabilize. Avalanches breaking on persistent weak layers are becoming harder to trigger, but the consequences are high whether a slide is one foot or four feet deep.</p>

    <p>Avalanches on these persistent weak layers&nbsp;can break wide and be triggered from lower angle terrain below or adjacent to steep slopes. Warning signs like collapsing or natural avalanches may not be present. Avoid slopes that are heavily wind loaded, identifiable by large overhanging cornices or big round pillows of snow, and avoid steep slopes where you suspect buried persistent weak layers.</p>

    <p>Smaller avalanches can also break within drifts of recent snow, and&nbsp;are most hazardous where debris can pile deep or push you into trees or cliffs (<strong><a href="https://www.mtavalanche.com/images/20/avalanche-beehive">photo</a></str…;). Travel on slopes protected from recent wind, and carefully assess the snowpack and terrain before riding on slopes steeper than 30 degrees. Today avalanches are possible to trigger and avalanche danger is MODERATE.</p>

    Upcoming Avalanche Education and Events

    Our education calendar is full of awareness lectures and field courses. Check it out and plan to attend one or two: Events and Education Calendar.

    COOKE CITY

    Every Friday and Saturday, Snowpack Update and Rescue Training. Friday, 6:30-7:30 p.m. at the Soda Butte Lodge. Saturday anytime between 10-2 @ Round Lake.

    WEST YELLOWSTONE

    Shooting cracks at Ross Peak, Bridgers

    Ross Peak
    Bridger Range
    Code
    Latitude
    45.85860
    Longitude
    -110.95600
    Notes

    From an email:

    "Skied from Bracket creek to the east facing glades below Ross Peak. At lower elevations very thin snowpack. As we got higher, snow had been significantly wind effected. Experienced several shooting cracks. At 8000 ft, snow was still only 50-75cm deep with variable wind slab. Did not dig a full pit, but hand shear tests showed the wind slab was very poorly bonded to the facets beneath. Winds were swirling and increased from calm to strong throughout the day. Blowing snow mostly filled in our tracks within about 30 mins."

    Number of slides
    0
    Number caught
    0
    Number buried
    0
    Slab Thickness units
    centimeters
    Single / Multiple / Red Flag
    Red Flag
    Advisory Year
    19-20

    Small avalanches in Hyalite on Flanders and the Mummy

    Flanders Creek
    Northern Gallatin
    Code
    SS-N-D1-O
    Aspect
    N
    Latitude
    45.44020
    Longitude
    -110.93100
    Notes

    From an email:

    "Beauty of a day up in Hyalite so long as you didn't mind the wind. The SW/W winds were cranking and clearly transporting snow all day at ridgetop (photo attached). Above 7500' we consistently found ~20cm of new snow from the storm earlier in the week on on top of a thin soft slab over small (but well developed) near surface facets. - A quick pit at 8900' on a protected 30 degree East aspect yielded no obvious slab and no propagation in tests but did show fractures along the new snow/old snow boundary and consistent deeper collapses in the buried crust-facet-sandwich. - We did notice a few recent natural avalanches on wind loaded north aspects in aprons below large cliffs and underneath large cornices (D0.5 - D1, max depth 1m, max width 30m) but these seemed to mostly be small soft storm slabs. - One recent crown near the top of the Mummy (30cm deep) looked to have run naturally on an old crust layer (photo attached) - We avoided slopes greater than 35 degrees and wind-loaded open slopes today and experienced no cracking, collapsing or avalanching where we travelled. - The next front rolled in rather quickly at 3pm with S2+ snowfall and ripping winds throughout the valley."

    Number of slides
    1
    Number caught
    0
    Number buried
    0
    Avalanche Type
    Soft slab avalanche
    Trigger
    Natural trigger
    D size
    1
    Bed Surface
    O - Old snow
    Problem Type
    New Snow
    Slab Thickness
    30.0 centimeters
    Images
    Natural avalanche crown on the Mummy
    Active wind loading on Flanders Ridge
    Slab Thickness units
    centimeters
    Single / Multiple / Red Flag
    Single Avalanche
    Advisory Year
    19-20
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