Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

You should be prepared for the potential of large avalanches every day you venture into the mountains this week as dynamic springtime weather transforms our snowpack. Once the sun has softened the surface, the likelihood of wet avalanches will increase. Choose safe travel routes far away from overhead hazards and take into account your return route home.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    There may be a battle between the nice springtime weather and unseasonable winds which will determine the likelihood of wet avalanches on Tuesday. As the snow surface starts to soften on sunny slopes, take the time to see if you are sinking into the snow past your ankle. If so, you need to put wet avalanches on your radar and look for other indicators that the upper snowpack is destabilizing such as rollerballs and pinwheels or snow shedding from trees and rocks. 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. Other wet avalanches such as wet slabs, cornice collapses, or glides could occur when these conditions are met and are very difficult to predict. Your best mitigation technique for all wet avalanche problems will be to head toward shadier slopes and keep aware of your overhead hazard.

    (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

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    The winds alluded to above should be significant for this time of year and slopes that do not see direct sunshine could still be holding cold and dry snow. This snow could be transported into shallow Wind Slabs or there could be some lingering slabs from this past weekend. Shady slopes produced multiple human-triggered slab avalanches in recent days 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 features to avoid. They will be more likely as you ascend in elevation 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. In areas with dry snow, you can use uptrack tests or test slopes to determine the slab potential and if blocks of snow are failing easily. If you find poorly bonded snow or suspect a terrain feature to be wind-loaded, you should seek out lower-angled options.

    (4/12/2021) This Wind Slab avalanche was triggered by a skier who was caught and carried. The debris triggered a second Wind Slab on a lower slope as it descended. [N aspect 4700'; Lower Slab: 4200' Photo: Renee Shapiro]

Avalanche Discussion

Observations were limited on Monday, but the sun was definitely out and temperatures started a climb that should continue throughout the week. Many aspects have been receiving direct sunshine and should be going through a melt-freeze cycle due to cool nights and warm sunny days, creating a firm surface crust. This crust may grow thicker throughout the week, but below it, you will still be able to find cold dry snow.  As the snow surface softens throughout the day on these sunny slopes, expect a continuation of the springtime shedding cycle that started on Sunday and is expected to produce wet avalanches, snow falling off trees or rocks, glide avalanches, and cornice collapses. This cycle will go through peaks and valleys over the next week as sunshine, freezing levels, and cloud cover fluctuate with the springtime weather. 

On slopes that do not see direct sunshine, a colder and more layered snowpack exists and was responsible for at least 5 notable human-triggered avalanches recently at Snoqualmie Pass. In two of these avalanches, individuals were caught and carried, which you can read about here and here.  The 4/7 and more prominent 4/9 interfaces have been confirmed to contain weak snow (near-surface facets and graupel) and should act as snowpack markers for you. We expect all avalanches to occur above the 4/7 interface on Tuesday, whether they are wet or dry.

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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