Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

The best indicator of avalanches is recent avalanches, and we have had plenty of those the past few days at Snoqualmie Pass. Consider recent history as you manage both dry and wet avalanche problems on Monday. Limit your time traveling on or below steep slopes that are in the sunshine and check for wind-loading before stepping into consequential terrain.

Problemi valanghivi

  • Loose Wet

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

    After a cool evening, temperatures will again start to climb on Monday, potentially reaching higher freezing levels than on Sunday. Expect wet avalanches to once again develop on steep sunny slopes as the snow surface starts to soften. Your first indicators that the upper snowpack is destabilizing will be rollerballs and pinwheels, snow shedding from trees and rocks, and the surface becoming wet and sticky. If you notice these signs, expect Wet Loose avalanches to follow and head toward shadier slopes. These slides often start at a point such as near trees or rocks, can entrain significant snow, and will fan out as they descend, possibly growing large and traveling long distances toward lower elevations. 

    We have multiple melt-freeze crusts and a layered upper snowpack. On slopes that see direct sunshine, this creates a potential point for pooling meltwater which could result in Wet Slab avalanches. You should use the same indicators and mitigation techniques as with Wet Loose avalanches. When in doubt, head toward shadier slopes.

    (4/11/2021) Wet Loose avalanches were observed in the Alpental Valley on Sunday 4/11 as sunshine destabilized recent storm snow and it started to shed from trees and rocks around noon. Skiers for scale.

  • Wind Slabs

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

    Slopes that do not see direct sunshine could still be harboring cold and dry snow, much of which may be wind-affected. Multiple human-triggered avalanches have been reported in the past few days occurring in these conditions, and weak snow has been identified within the snowpack on northerly aspects. Take a look for textured snow surfaces, or pillow-like piles of snow to help you identify wind-loaded slopes to avoid. They will be more likely as you ascend in elevation on slopes with a northerly tilt and often form near rocky features such as confined gullies or at the base of cliffs. You should also look for them on leeward slopes near ridgelines or on convex rollovers. You can use uptrack tests, hand pits, or test slopes to determine the slab potential on shady slopes and if blocks of snow are failing easily. If you find poorly bonded snow or suspect terrain to be wind-loaded, you should seek out lower-angled slopes. 

    (4/11/2021) The site of an avalanche involvement on Saturday 4/10. A skier triggered a wind slab and was caught, carried, and fully buried after being swept off a cliff. [NW 5440]

Avalanche Discussion

We have knowledge of 5 notable human-triggered avalanches in the past few days at Snoqualmie Pass, two of which were avalanche involvements where people were caught and carried. One of these involvements resulted in a full burial and injury to the skier involved. These near-misses and involvements come less than a week after massive Glide avalanches descended into the Alpental Valley, narrowly missing multiple parties. 

The snowpack around Snoqualmie Pass is in a state of flux and both wet and dry avalanches pose a hazard right now. The 4/7 interface, buried close to 2 feet deep contains weak graupel sitting above it and was the failure point for the avalanche involvement on Friday. The 4/9 interface is about a foot below the surface and contains a layer of equally weak near-surface facets. This was identified as the failure point for the avalanche involvement on Saturday afternoon. These interfaces and weak snow will persist on slopes that hold cold dry snow or could even be wetted and fail on slopes that see direct sunshine. On slopes on the southern end of the dial, sunshine will continue to destabilize the recent 2 feet of storm snow and produce wet avalanches. These are totally unpredictable and can come in many forms. Wet Loose, Wet Slab, Glide, Cornice failure, take your pick on any given day and roll the dice. Snow shedding from trees and rocks can help trigger these avalanches on any slope, and as we saw last weekend, they have the potential to grow large and descend to lower elevations. 

Monday will be a continuation of the springtime shedding cycle that started on Sunday when NWAC forecasters in the field observed multiple Wet Loose avalanches and snow shedding from trees and rocks. The cycle will go through peaks and valleys over the next week as sunshine, freezing levels, and cloud cover fluctuate with the springtime weather. We’ll try to guide you with our ratings of Considerable or Moderate letting you know which days have a higher likelihood, but wet snow problems are nearly impossible to predict and you should be prepared for the potential of large avalanches every day you venture into the mountains. Choose safe travel routes far away from overhead hazards such as cornices or glide cracks, and take into account your return route when planning your trip for the day. Keep your decision-making conservative and consider dialing it back until more stable snowpack conditions persist.

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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