Boletín de aludes

West Slopes South

Northwest Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

You could trigger surprising avalanches large enough to be deadly on Sunday. Look for obvious signs of instability such as recent avalanches, cracking in the snow, or whumpfing collapses as indicators to dial back your terrain selection. Wind-loaded slopes will remain the most likely place for you to trigger avalanches and should be avoided.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    Recent avalanches have failed on persistent grain types in the Crystal backcountry. Some unusual avalanches at Mt. Saint Helens reported through our observation platform appear to have persistent characteristics. That’s enough info for us to start talking about persistent slabs in the West South. These avalanches are very dangerous and difficult to predict. They can be triggered from long distances, break in surprising ways, and propagate widely across terrain features. You should look for red-flag signs of instability such as shooting cracks and whumpfing collapses as you travel to help clue you into their existence. If you notice these signs of instability or find weak snow grains in your pits sitting above the 1/13 crust, put plenty of space between yourself and slopes 35 degrees and steeper.

    (1/29/2021) Multiple slabs were remotely triggered from a far distance by a snowmobiler on Mt. Saint Helens on Friday (1/29). There were multiple other slides remotely triggered and observed on the same day. [Photo: Kurt Heine]

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    The winds should continue to blow throughout the zone on Sunday, building new Wind Slabs or thickening existing slabs. Look for Wind Slabs to be more reactive near rocky features such as gullies and cliffs, or on leeward slopes near ridgelines. Some of these slabs may be sitting on those buried weak snow grains, causing them to break in surprising ways. Other slabs may have multiple density changes from the past few days to fail on. Use test slopes to check the reactivity of all of the snow sitting atop the 1/13 crust to see how it reacts to your weight. Look for textured surfaces, smooth pillow-like piles of snow, or fresh cornices to key you into wind loaded slopes you should avoid.

    (1/28/2021) This avalanche was remotely triggered by a skier in the Crystal backcountry on Thursday in wind loaded terrain. You can see the shooting cracks initiating from where the skier is standing.

Avalanche Discussion

Snow totals on Saturday were a bit less than expected, but on the ground observations let us know that the wind was certainly moving the snow around, increasing the snow depth atop the 1/13 AR crust. We still believe that these areas of wind-drifted snow are the most likely location to trigger an avalanche throughout the zone. In the Crystal backcountry, weak snow grains called near-surface facets have been positively identified sitting above the crust. Multiple small avalanches and lots of signs of instability such whumpfing and shooting cracks have been reported by both professionals and recreationalists alike in this area, particularly in wind-loaded terrain. As temperatures warm and precipitation falls on Sunday, we could see more slab development or heavy snow over weak snow in non-wind affected areas, creating the potential for more widespread avalanches.

We feel like we have enough information at this point to add Persistent Slab as an official problem but may not have all of the information we need to get a complete picture of the zone. We still do not have confirmation of these grains in other areas of the zone besides Crystal. However, two good public observations have led us to believe that persistent grains have been the culprit in producing large avalanches (D2.5) on Mt. Saint Helens. We still don’t know about White Pass, Paradise, or all of the areas in between. This problem may not exist everywhere and could produce different sized avalanches based on your location. That said, you may want to dial it back a bit more than you typically do during Considerable avalanche danger. If you happen to be in a location where a persistent slab avalanche is triggered, it could be large and costly. Digging down to the 1/13 crust and positively identifying these weak snow grains is the only way to tell if the problem exists in your area. If you do not find them, you should not immediately rule persistent slabs out, but continue to collect more information and ease into terrain. Please help us out by letting us know if you see (or don’t see) avalanches, cracking, whumpfing, or weak snow on Sunday by submitting a public observation. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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