Lawinenlagebericht

East Slopes South

Northwest Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

Natural avalanche activity should taper on Thursday, leaving slopes primed for human-triggers. Some slides could break into old snow layers, propagating widely or wrapping around terrain features. Give the snowpack time to heal by avoiding all slopes over 35 degrees.

Lawinenprobleme

  • Storm Slabs

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

    Several waves of precipitation, fluctuating freezing levels, and strong winds have resulted in a layered upper snowpack. You’ll need to check the recent storm snow for weak interfaces and its bond to the old surface by digging. Small test slopes and uptrack tests won't cut it when the snow is this deep. Heavy snow over weak snow, layers of weak grains such as graupel, or wind-drifted slabs hidden below the surface are just some examples of potential failure points. Slabs should be larger as you ascend in elevation or in wind-loaded terrain. You’ll need to contend with storm slabs, wind slabs, and loose avalanches as you pick your way through the mountains. Regardless of the avalanche problem, you’re more likely to trigger one on slopes over 35 degrees.

    (2/27/2024)

    This slab failed as a ski patroller traversed lower on the slope. It reportedly failed on the 2/14 interface.

    Photo: Crystal Mountain Pro Patrol

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2.5

    This week has stressed weak layers in the upper snowpack. Continued snow and wind on Wednesday night and Thursday will be the final test to see if these layers become activated. If they do, avalanches could fail in surprising ways by spanning far distances, breaking above you, or wrapping around terrain features. They could even be triggered from flat terrain as you're riding along. The poor snowpack structure is confirmed, and the slab has developed; the only question remaining is what will it take to trigger one? Try not to find out for yourself. Put plenty of space between you and slopes over 35 degrees where triggering one of these avalanches is more likely.

    (2/22/2024)

    A skier triggered avalanche (D2) on facets above the early February crust in the neighboring East Central zone. The crown was 100' wide x 4"-1.5' deep and it was triggered from below on a 30-degree terrain. It ran to either side of the low-angle slope. Longs Pass, W, 6,200ft

Avalanche Discussion

By Thursday morning, we should be on the tail end of a multi-day storm cycle that dropped a blanket of fresh snow across the East South zone. Temperatures, wind speeds, and precipitation rates should all decrease throughout the day. That leads us to believe that widespread natural activity will likely have passed by the time day breaks, allowing us to lower the hazard rating. 

That doesn’t mean it’s not dangerous out there.  The big uncertainty still surrounds the ability to trigger a slab avalanche on persistent grains. Areas that have received the most snowfall during this storm, such as near Bumping Lake, will have larger and potentially more sensitive slabs. Observations have been limited by the ferocity of this storm not just in the East South but in neighboring zones as well. On Wednesday, an NWAC forecaster close to the West South/East South border reported wind-loaded slopes failing easily under their weight. Weak grains were identified on top of the Early February Crust (EFC). 

Last week, an NWAC forecaster in the Darland Mt area found weak, faceted snow just above the stout EFC crust and also over a thin, breakable crust buried on 2/14 on southerly aspects. This persistent weak layer has produced avalanches in neighboring zones.

 Your avalanche, snowpack, or weather observations are extremely valuable to the avalanche community. Help create a more accurate avalanche forecast by submitting your observations here. 

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