Avalanche forecast

West Slopes North

Northwest Avalanche Center
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Avalanche danger

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

A late-season storm is increasing the danger of slab avalanches in new and wind drifted snow layers. Avoid steep, open terrain, especially where you suspect the wind has created deeper and easier to trigger slabs. Brief periods of clearing sky could initiate wet avalanches on sun-exposed slopes.

 

Avalanche problems

  • Storm Slabs

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

    Additional snowfall overnight will add up to another foot of snow over the 4-8” received Monday. You are most likely to trigger an avalanche in leeward mid and upper elevation terrain. Steep terrain in wind sheltered areas could also produce slab avalanches, especially on shaded, northerly aspects where storm slabs might rest on surface hoar or other weak snow grains. 

    Approach all avalanche terrain with caution and identify and avoid steep wind loaded slopes. Look for signs of recent wind loading like differences in snow texture and depth as you gain elevation and change aspects. Cornices and wind eroded or scoured snow surfaces might point to areas that are likely to hold deeper slabs. Simple snowpack tests should give you a good indication as to the reactivity of new storm and wind slab layers but will not tell you much about layer bonding at deeper interfaces. As always, give the highest priority to obvious signs of instability like recent avalanches, shooting cracks, and whumpfing. 

    Example of storm slab avalanche in Canyon Creek in 2021.

Avalanche Discussion

With the bulk of the snowfall forecast for the overnight hours, avalanche danger should be the greatest in the morning with a gradual increase in stability throughout the day. The caveat is that conditions will remain dangerous if heavy snowfall persists longer than forecast or in areas seeing continued wind-loading. Wet loose avalanches are possible if new snow warms, becomes wet, and weakens on sun-exposed slopes or at low elevations. Minimize travel on and below slopes where you see wet loose avalanches or other signs of instability during sun breaks or with rising temperatures. 

A period of drier weather and generally clear skies ended Sunday evening as a well-developed frontal system moved into the Cascades. Heather Meadows picked nearly 1” of precipitation in 8" of snow with other weather stations in West North receiving similar amounts. There were no observations regarding avalanche activity or the bond of new snow layers as of Monday afternoon. The new snow is falling on a variety of surfaces from a slick, stout crust on solar aspects to cold and dry snow on the most shaded aspects. Some shaded slopes also held onto surface hoar, facet, and even graupel layers that could enhance the reactivity and propagation of storm slabs. Though not widespread, they are another reason to approach avalanche terrain with additional caution on Tuesday.

 

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