Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

The bond between recent storm snow and the underlying surface is still less than ideal, and continued winds could form new slabs or deepen existing ones. Wind slab avalanches remain a concern tomorrow, particularly on steep, unsupported terrain at higher elevations where slabs are thicker and more reactive. Consider wind-loaded slopes guilty unless you can safely prove otherwise.

Problemi valanghivi

  • Wind Slabs

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

    As we get further out from the weekend's storm, obvious signs of instability are decreasing. However, lower density storm snow over the 1/10 crust is still yielding mixed results in snowpack tests, and we just don't fully trust this bond yet. It will likely take a steep slope with a thicker slab to trigger an avalanche, and unsupported or convex features are all the more suspect. The tops of chutes, aprons at the base of cliffs, and slopes below steep ridge lines are all likely locations to find this problem. You can use hand pits and small test slopes to gauge for reactivity, but you need to be sure that the test slope is representative of the start zone on the slope you are considering. Subtle differences in slope angle, aspect, and wind-deposition patterns can make a huge difference in slab presence and reactivity. The simpler and safer move is to give wind-loaded slopes over 35 degrees another day to settle out. Choose supported, planar slopes where you don't see signs of wind-drifting.

    (1/13/2025)

    A look up at the crown of a human-triggered wind slab avalanche from 1/11 on a northeast-facing slope at Alpental. This avalanche broke on a 40-degree slope at the base of cliffs–an ideal location for a wind slab avalanche on Tuesday.

    Photo: Josh Lipkowitz

  • Loose Wet

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

    High clouds prevented the southern half of the compass from seeing significant warming on Monday, leaving many slopes still waiting for their first good shot of sun and warmth since the storm. If the sun comes out and stays out on Tuesday, the chance for wet loose avalanches will increase on slopes facing the sun. This problem gives some clear advanced warning signs. Look for rollerballs, pinwheels, snow shedding from trees, and a moist or wet snow surface. If you see any of these, stay off of and out from under steep slopes in the sun. You can shift your aspect to a shadier slope to mitigate this hazard.

    (12/23/2024)

    Wet-loosed debris that released naturally in the sun earlier this season. Similar activity could occur in the coming days.

    Photo: Summit at Snoqualmie Pro Patrol

Avalanche Discussion

On Monday, NWAC forecasters again went hunting around the Pass to gather some more information around the 1/10 crust. Numerous human-triggered avalanches on Saturday, including a 4-person catch and carry with injuries, likely occurred at this interface.

We found very similar structure on Monday to what we found on Sunday, and this matches other area observations as well. At the mid and upper elevations, specifically above about 4500-4800', the stout 1/10 crust sits below 6 to 12" (and sometimes deeper) of surface snow. Depth of snow above the crust is largely a function of elevation and wind-drifting. At the base of the storm snow sits a few mm-cm of soft 4F precipitation particles/decomposing fragments. Virtually every test we have performed (hand shears, CTs, ECTs, etc.) have failed on this thin layer of soft snow above the crust. Wind-loaded areas are where we are concerned about this structure. On Monday, we had a propagating result in a large column test at the crown of a human-triggered avalanche from Saturday. This avalanche occurred on a 40-degree slope at the base of cliffs. The slab was quite firm and deeper than in other large column tests that did not propagate, and is likely representative the type of terrain and slab character/depth where you could still find this problem. While we don't yet have confidence in the bond, we don't expect this problem to be long lived. This grain type isn't typically persistent, and it should settle out with a few days of calm weather without additional loading. 

In the meantime, we are still keeping big terrain off of our run list and we think you should too. It just isn't trustworthy yet and more days out from the storm will only make it harder and spottier to assess reactivity as the problem becomes more and more stubborn. 

As for the wet loose issue, the clouds spoiled the beach party on Monday. We found lots of unaffected snow on west and southwest aspects, which makes us think that things could start to shed some if the sun comes out in force on Tuesday. If the clouds keep things at bay, we may punt this problem to Wednesday.

Finally, and not to sound like a broken record, but the travel at the lower elevations is rugged. Frozen tree bombs, icy surfaces, and open cliffs abound. It makes you wonder if all your fillings are still intact. Go slow, leave time to navigate this challenge, and don't underestimate the injury potential late in the day when you have to deal with these conditions.

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