Lawinenlagebericht

Tetons

Bridger-Teton Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

New snow yesterday combined with strong winds and older loose snow on the ground have built wind slabs that may be reactive to your weight today. Look for and steer clear of drifted and wind affected snow, primarily above 8,500' and especially in steep, rocky terrain along ridgetops. These slabs could be up to two feet thick, and three feet thick in a few areas; large enough to carry or bury a person in the wrong terrain. A lingering persistent slab problem also exists and could lead to larger human-triggered avalanches and thicker slabs. Evaluate snow and terrain for both of these avalanche problem types if venturing into steep terrain today.

One natural avalanche was observed yesterday on the East Face of the Middle Teton with other small natural avalanches also reported.  Recent avalanche activity like this is a sign that  snowpack has likely not yet settled and stabilized.

 

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Wind speeds following the storm this past weekend were light to moderate with only isolated wind slabs, mostly in the alpine and upper elevation areas. Winds cranked up into the 30-40 mph range with gusts into the 50's mph from the southwest in the early morning hours yesterday before shifting northwest. Between available loose snow on the ground and new snow falling yesterday, lots of snow was available for wind slab development. You're likely to find drifted snow ranging from soft and reactive to firm and stubborn in wind exposed areas in a variety of locations due to the wind shift.

    These wind slabs have only had about half a day to heal and are likely to be sitting upon soft new snow. Look for signs of wind affect on the surface and listen for hollow sounding firm slabs. Shooting cracks or drum-like sounds are an indication that you've found this avalanche problem.

    (2/6/2023)

    Two separate parties were involved in avalanches in a wind exposed area outside JHMR day before yesterday. This close call illustrates the importance of preparedness and careful terrain  selection (Ralph's Slide observation).

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    1.5–2.5

    What's the problem? The snowpack contains several layers of crusts with nearby weak faceted snow and buried near surface facets even without a crust nearby. The most recently formed weak layer, and one that seems most likely to be triggered, is a thick layer of near surface facets from a dry spell prior to the Jan 26-28 storm. The layer shows a tendency to propagate a crack and while there haven't been reported avalanches on this layer for over a week, we aren't out of the woods yet. Small amounts of new snow, such as we received yesterday, added more strain to the layer.  

    Where: Shallower areas in the snowpack with a slab over weak snow are the main concern.  Steep, rocky slopes peppered with rocks and signs of wind effect are locations to watch as well as solar aspects with thicker crusts which have more, and weaker facets. Alpine terrain exposed to wind scouring and drifting creates a thinner snowpack ripe for the development of facets and should definitely be assessed carefully.

    What to do about it? When in doubt probe and dig or simply find someplace else to ride. Some of the weak snow grains are tricky to identify visually in pits but small, loose and angular grains that aren't well bonded to each other or the adjacent crust are what you are looking for. Triggering a persistent slab avalanche is unlikely but not impossible so choose terrain carefully.

    Deep Persistent Slab: In addition to persistent slab problem type, a  deeper weak layer persists in middle and upper elevations on southeast through west aspects. These layers appear to be dormant but could awaken with a big storm or large load, such as another avalanche. The resulting avalanche could be up to five feet thick and carry severe consequences. 

    Note the clear and dry spells on the Snowpack Tracker between storms. Very cold nights and sunny days on Jan. 20-24th and Jan. 30th - Feb 1st drove the faceting process.

Avalanche Discussion

Looking at row upon row of numbers from regional weather stations this morning paints an incomplete picture of current avalanche conditions on the ground. Limited visibility and few observations yesterday don't fill many gaps though an early morning report of a natural avalanche in the Park and many small storm slab avalanches yesterday help to complete the picture. Today, you are likely to find a variety of signs of potentially unstable snow due to wind direction shifting 90 degrees pre- and mid-storm, aprons of loose snow piled on soft snow beneath steep terrain features, and lurking beneath it all is a concoction of crusts and facets that appears to be dormant though continues to add a question mark to otherwise confident terrain assessment. Sky conditions should allow for a good visual assessment of snow surfaces, cornice growth, and other signs of potential wind slabs. Keep the deeper weak layers in mind today, especially in alpine areas where unsupported slopes, a variable or scoured thin snowpack could conspire to bring the weak layers of persistent weak snow grains within range of triggering.

 

 

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