Lawinenlagebericht

Banner Summit

Sawtooth Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Triggering a 1-2 foot thick avalanche is possible—particularly where wind forms drifts or hard layers at the snow surface. While unlikely, we can't rule out triggering a huge, 4-5 foot thick avalanche—especially on very steep, rocky, wind-affected slopes. The danger will increase tonight as another storm impacts the area. 

Lawinenprobleme

  • Wind Slabs

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

    The mountains near Banner Summit picked up 3-7" of snow since yesterday morning. Snow will continue today, adding an additional 2-4". Wind blew moderate yesterday from the W, likely building small wind slabs in exposed terrain. This problem will be most widespread at upper elevations with greater snow amounts that are exposed to stronger wind. 

    Wind speeds will be light for a good portion of today but will increase this afternoon. Remember that fresh slabs can form in a surprisingly short amount of time. Look for active wind-loading and cracking in the snow surface. Small wind slab avalanches (see video to right/above) can be great triggers for more deeply buried weak layers. Any avalanche that steps down to these persistent weak layers will be large and destructive.

  • Persistent Slabs

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

    Around Banner Summit, most of the recent observed avalanche activity failed on a layer of surface hoar and small faceted grains. We've seen this layer present itself as surface hoar, small facets and surface hoar, small facets, or facets above a crust (observation). Stability test results and a lack of avalanche activity the past few days indicate this layer is strengthening, but we can't forget about it yet; human-triggered slides remain possible. You are most likely to trigger one in "prime time" avalanche terrain—slopes over about 35*—that has been loaded by the wind.

    ADDITIONAL DISCUSSION:A weak layer of facets sits near the base of the snowpack buried beneath a stout 4-5' thick slab of snow. It is difficult for skiers and sledders to impact this layer because the slab over it is so thick and dense. It would take a dose of bad luck to trigger one of these deep slab avalanches, but it could happen in very steep, rocky, wind-affected terrain. 

    (2/4/2021) This avalanche failed 2' deep on buried surface hoar. This weak layer has presented itself as surface hoar in some areas and small facets in others. NE, 8400', Copper Mtn.

Avalanche Discussion

Snowfall has returned to the northern and western portions of the forecast area as a series of Pacific storms impact the region through tomorrow. You can see our updated storm table here, or check out your favorite weather station here. Snowfall amounts are modest so far, with 3-7" in the mountains around Banner, the Sawtooths, and the western Smokys. An additional 2-4" is expected in these areas today as well as another 6-8" tonight through tomorrow. 

All said and done, we're looking at 10-20" of new snow by Saturday afternoon. This amount of snow and some wind is plenty enough to create avalanche problems on its own. Yesterday, Ben could hear the wind at upper elevations around Banner Summit and observers noted moderate to strong wind along the high peaks of the Smokys. Although we'll see a little lull in the wind today, it's forecast to increase as the next shot of snow arrives this afternoon. 

What, if anything, this amount of snow and wind-loading does to our buried weak layers is uncertain. Recent observations of the facet and surface hoar layer buried in late January are showing signs of improvement. The last likely collapse associated with this layer was one Ben experienced in the Fishhook drainage of the Sawtooths on Monday. Even still, I think we're better assuming this added snowfall may wake things up until proven otherwise. Where and if we see activity on existing persistent weak layers will give us great information moving forward.

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