Bollettino valanghe

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Fri
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2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

You may be able to trigger avalanches up to 2 feet thick where the wind has drifted snow. Loose snow avalanches will release on very steep slopes that face the sun. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Expect to find thin, fresh wind slabs in the alpine. Yesterday a professional observed the crown of a slab avalanche in wind-affected, upper elevation terrain of the central Sawtooths. Yesterday in the Smoky Mountains, I found small wind slabs up to 1' thick (photo). Similar drifts were reported south of Smiley Ck (photo). Observers noted strong wind in the alpine, lifting low-density snow into plumes that extended for hundreds of feet into the air. Wind speeds will ease this morning, but ramp up again to build additional small slabs this afternoon and evening.

    Wind slabs often form near or just below ridgelines, on the sides of cross-loaded chutes, or on aprons below steep cliffs. Many of them rest on slick crusts. This means they may be easy to trigger, break wider than expected, and will pick up speed quickly as they travel downslope. 

    Pay attention to how the snow feels under your skis or boards. If the snow surface suddenly stiffens or becomes more supportable, you've found a wind slab. Cracks shooting out in front of your skis or boards are a red flag warning you to be cautious. Surface clues like dunes or ripples can tell you the wind has been at work.  

    ADDITIONAL DISCUSSIONWeak layers consisting of crusts, facets, and surface hoar, exist in the upper part of the snowpack. The weakest snow we've seen is on the shady half of the compass, spanning upper and middle elevation terrain (photo). This persistent slab occurred last week after a small storm near Galena Summit (photos and details here). Better visibility today will allow us to see whether Tuesday's snow and recent wind were enough to produce similar slides. Choose more conservative terrain on shadier slopes as you climb in elevation, particularly where the wind has stiffened the snow surface or formed drifts.

    (3/9/2022) This small wind slab formed just below an exposed ridge on an E-facing slope at 9,600' in the Smoky Mountains. These small slabs ranged from 15-25 cm thick in this location and tapered quickly in more sheltered terrain.

  • Loose Dry

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Certain
    Dimensione
    1–1.5

    The sun will initiate loose snow avalanches on very steep slopes. Avalanche activity will start on E-facing slopes this morning, follow the sun as it moves through the southern sky, and end on W-facing slopes in the afternoon. These slides commonly initiate near warm rocks, fanning out and collecting snow as they go. Human triggered loose snow avalanches (or sluffs) are also possible on very steep, shadier slopes that are sheltered from the wind.

    Although likely to be small, sun-induced avalanches will be numerous and can travel quickly on the slick surfaces beneath them. Pay attention to the terrain above you. Large slopes can produce slides big enough to knock you off of your feet and carry you places you don't want to go. 

Avalanche Discussion

Tuesday's storm and the subsequent arrival of frigid arctic air have it feeling very "wintery" out there. However, the winter feel is not relegated to just the weather, the upper 1-2' of the snowpack is looking "wintery" as well. Weak layers including multiple crusts, layers of facets, and surface hoar lie beneath the recently fallen snow. The composition of these layers is highly variable and depend on aspect, elevation, slope angle, and the amount of recent snowfall. 

As a quick example, you can see the contrast between this S-facing pit and this N-facing pit I dug yesterday in the Smokys. These pits were less than a 1/4 mile from each other and at similar elevations. The point here is that it's complex. Not only do the weak layers change, but the thickness and stiffness of the slab vary as well. In some areas, you'll be scratching around in "dust on crust". Around the corner, you could run into a stiffer, sensitive drift.

Keep these potential weak layers in mind today. No matter where you head, you're most likely to trigger a slab avalanche where you find stiff, recently formed slabs. With increased complexity comes increased uncertainty. To deal with this, SAC forecasters are beginning to avoid large or high-consequence starting zones over 35* where these weak layers might exist. 

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