Lawinenlagebericht

Banner Summit

Sawtooth Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
4 · Gross
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

You can trigger avalanches large enough to bury you on many slopes today. A storm brings up to a foot of new snow by 5pm and sustained strong winds. Avalanche danger will rise to become very dangerous throughout the day.  Avoid traveling on or underneath slopes steep enough to avalanche. Slides can be triggered from long distances away from steeper slopes and can run into gentler terrain below. 

Lawinenprobleme

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    1–2

    The ongoing storm will bring up to a foot of new snow and sustained strong winds to the western end of this zone. Expect to find a range of problems involving this new precipitation. At upper and middle elevations, you'll find reactive wind slabs large enough to bury you and you may be able to trigger loose snow avalanches that run fast and far on weak, slick surfaces. In sheltered middle elevation terrain, expect to easily trigger slides involving all of the new snow that may have a loose characteristic to them, or be more consolidated slabs. Enough recent snow will fall that these new snow avalanches will be large enough to bury you. Importantly, natural and triggered slides involving the new snow can trigger the much larger, more destructive persistent slabs described below. 

    Steer clear of terrain traps such as gullies, depressions, and cliffs that can increase the consequences of new snow avalanches even in more benign looking terrain. 

  • Persistent Slabs

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

    Several weak layers are buried within the upper 2 feet of the snowpack. With the additional foot of snow that will fall and strong winds throughout the day today, more stress is being added to these weak layers. Multiple human-triggered avalanches involving this snow were reported in the past 10 days (Profile drainage, Alturas Lake Creek, near Dollarhide Summit). This weak snow has produced avalanches on both shaded slopes and slopes facing the sun. On sunny slopes you'll find a sun crust with associated facets. On shaded slopes you'll find a few thin rain crusts with small facets sandwiched in between. 

    This weak layer is highly variable. On some slopes it is well bonded, while on others it is producing large avalanches. You may find good stability on one slope and then trigger an avalanche when you change to a nearby slope. Cracks shooting out from your skis or machine are a clear sign you've found an unstable slab. The human-triggered slides that have failed on this layer have been triggered from a distance (remotely). 

    ADDITIONAL DISCUSSION - DEEP PERSISTENT SLAB: The weak layer that produced widespread avalanche activity in January is now deeply buried here. If you dig down, you'll eventually find it buried underneath a very dense 3-5 foot thick slab of snow. Triggering one of these monsters is unlikely, but the result would be catastrophic. The most likely terrain for making one of these beasts is steep, rocky, wind-affected terrain where the snowpack has thinner spots that give you access to the weak layer. You can watch a video describing this problem here.

Avalanche Discussion

A winter storm will bring up to a foot of new snow to the Banner Summit Zone by 5pm tonight. The new snowfall totals coupled with the sustained strong, westerly winds that are unusual for this zone will be the main architects of new instabilities in the snowpack. Even foot of snow is enough to create avalanches running on the new / old snow interface that can be large enough to bury you. Add in sustained strong winds that can load even larger slabs into starting zones, and these slides definitely will be large enough to bury you.

In sheltered middle elevation terrain, expect to easily trigger slides the new snow that may have a loose characteristic to them, gaining mass and speed as they run downhill.  The Banner Summit Zone in particular has quite a bit of mid and lower elevation terrain traps, or features that can increase the consequences of a smaller avalanche. Terrain traps such as gullies, creeks, and depressions can multiply these consequences even in the somewhat benign-looking terrain that lives throughout a large portion of this zone. At upper and middle elevations, you'll find reactive wind slabs and you may be able to trigger loose snow avalanches that run fast and far on weak, slick surfaces. Importantly, natural and triggered slides involving the new snow can trigger the much larger, more destructive persistent slabs. 

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