Lawinenlagebericht

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 7 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Recent snowfall and several days of wind have increased the chances of triggering an avalanche in upper elevation terrain. You’re most likely to trigger a slab avalanche in freshly formed wind drifts. Underneath these drifts, weak snow near the bottom of the snowpack continues to pose a threat. To reduce your risk, steer clear of slopes where the wind has stiffened the snow surface.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    Early-season persistent weak layers in the lower snowpack are widespread throughout the Galena Summit & Eastern Mtns zone. What's less consistent is the nature and stability of these layers. 

    The thin, windswept snowpack of the Boulder Mountains did not respond well to Monday's wind event, and several large, natural persistent slab avalanches occurred as a result (see observation and photos below). While observations from the White Clouds are limited, this range may have the trickiest snowpack in the forecast area. Especially weak, faceted snow near the ground is buried beneath a dense slab more than 4 feet thick. Last week, Ben visited an avalanche that released a week ago (photo to right). It broke over 500 feet wide, 4-6 feet deep, and covered snowmobile tracks from the previous day. Meanwhile, these same weak layers in the Galena Summit and Baker Creek area are showing better stability.

    While triggering a persistent slab avalanche is generally unlikely, it remains possible in terrain with the following characteristics:

    • Steep: slopes in prime-time avalanche terrain around 35-45 degrees.
    • Wind-affected: heavily wind-loaded by past or recent wind events.
    • Alpine flavor: complex, windswept terrain with rock ribs, cliff bands, or convexities.

  • Wind Slabs

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

    Since the middle of the week, the Galena Summit & Eastern Mtns zone has picked up around 8-12+ inches of new snow. That would be well and good except that the snowfall has been accompanied by persistent moderate to strong W to NW winds. As a result, fresh wind slabs have formed on the lee sides of ridges and other exposed terrain features. Over the past several days, several small natural and triggered wind slab avalanches have been reported in the central Sawtooths, near Galena Summit, in the Boulder Mountains and in the Wood River Valley.

    Warm temperatures yesterday and overnight have helped these wind slabs bond to underlying snow surfaces, but more snow and wind today will create a fresh batch that may be sensitive to your weight. Fortunately, these wind slabs will be easy to identify. Watch for snow that is denser than snow found on wind-sheltered slopes and tell-tale clues such as surface texture and a pillowed, drifted appearance. Avoid steep slopes where you find these indications of recent wind loading.

Avalanche Discussion

The wind is probably one of our least favorite winter weather factors, second only to the "r" word. But since last Monday, it has been the primary force behind our avalanche conditions. As you likely know, when the wind is sufficiently strong, it picks up snow from one spot and puts it in another. While the snow particles blow through the air or bounce along the snow surface, they break up and become smaller. The smaller snow grains more easily pack into dense, stiff, or even hard wind drifts once they're deposited. And—ta-da—you have a wind slab.

In areas where these wind slabs form atop snow surfaces that aren't persistent weak layers, such as softer new snow, older wind slabs, and crusts, the period of instability is often short-lived. Warmer temperatures can help to speed up the process of stabilization. The trouble is that consistent winds over the past several days formed fresh, touchy wind slabs even as old wind slabs stabilized. With any luck, today will be the last day of the persistent winds and wind slabs will get a chance to heal once and for all.

The more complex issue with the recent wind loading is where the wind slabs are adding additional weight to buried persistent weak layers. Where our snowpack remains shallow and especially weak—for example the windswept Boulders and the Wood River Valley—the recent wind loading kicked off a round of natural and triggered avalanches. This problem is likely to persist longer than the "pure" wind slab problem and has the ability to produce a much larger avalanche.

Fortunately, areas with recent wind loading are easy to identify with "look and feel"-type observations. The snow surface on wind-affected slopes usually has a different texture and will be denser and more cohesive than the snow found on sheltered slopes. Pillows and dunes indicate areas where the wind has deposited and drifted the blowing snow. Keeping your eyes open for these clues, and avoiding steep slopes where you find them, will help you avoid most of the avalanche risk that currently exists in our area. This is especially true if you find yourself in alpine areas or where the snowpack remains on the shallow side.

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