Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

Avoid all avalanche terrain due to very dangerous avalanche conditions near and above treeline as rain destabilizes and dense snow overburdens dry snow. Natural and human-triggered wet or dry snow avalanches will be large, widespread, and difficult to survive. Below treeline, choose forested areas and slopes less than 35 degrees that are not exposed to large avalanches from above.

Problemi valanghivi

  • Loose Wet

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

    Heavy snowfall near and above treeline followed by rapid warming later Monday night into early Tuesday. Natural avalanches are likely and human triggered avalanches are very likely. Snow levels are expected to rise from 4500 Monday evening to 6500 Tuesday morning through the remainder of the day. Dry snow destabilizes very rapidly when it becomes wet, creating short windows of the highest instability. The snowpack prior to the current storm cycle is consolidating and well set up to handle a load. Thus, we expect most avalanche activity to entrain the snow that falls from Monday onwards, with the largest and deepest storm totals, and therefore deepest avalanches, at higher elevations. Avoid anywhere that avalanches can start, stop, or run. Below treeline, where less snow has accumulated and rain continues to fall on the snowpack, boot penetration greater than 6" and rollerball activity serve as a reminder that Wet Loose avalanches may be triggered on any slopes steeper than 35 degrees.

    A sun crust formed on steeper southerly slopes during the nice weather Saturday and there is a chance of an isolated wet slab running on the crust. Further south in the Mt. St. Helens area the snowpack is likely more layered and this potential may be greater where we don't have recent snowpack information.

    Example: Powerful Wet Loose Avalanche

  • Storm Slabs

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

    Near and above treeline, heavy dense snow will load lower density layers from earlier in the storm cycle, creating widespread slabs 6-24" slabs that you can easily trigger within the recent storm snow. Given the heavy, dense snow these slabs will have plenty of force to harm or kill you. Firmer over weaker snow will confirm the very dangerous conditions. A rapidly ascending rain line early in the day may quickly confine storm slabs to above treeline areas. Keep things simple and avoid all avalanche terrain near and above treeline where slabs can start, stop, or run. Given the expected 6500 ft snow levels, these slabs may exist only above the treeline, in which case, Wet Loose problems will be the only concern near treeline.

    Example: Large storm slab avalanche.

Avalanche Discussion

By the time you enter the terrain on Tuesday, snow lines will have crept up the slope into the near treeline band and will creep higher to the base of the above treeline band. Elevations that continue to see dry snow or a rain to snow transition will be the most dangerous, producing reactive avalanche cycles. Above or below that transition zone, conditions will be plenty dangerous as well, with storm slabs growing rapidly under intense precipitation rates and loading lee slopes with wind. At lower elevations, rain will wet shallower recent snow.

This atmospheric river marks a drastic transition from this past weekend into Monday. Observations from the West-South zone this weekend suggest a generally strong and well settled upper snowpack. Avalanches remained limited to specific features, very steep terrain, and were small. A sun crust formed on steeper southerly slopes during the nice weather Saturday. 

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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