Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Winds and snowfall will taper off on Monday, but it may be possible to trigger avalanches in wind drifted snow near ridges. Consider sticking to wind-sheltered terrain or traveling on lower angle routes to gain ridge tops. Although the chances are low, it still may be possible for avalanches to step down to deeper weak layers and become surprisingly large. 

Avalanche problems

  • Wind Slabs

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

    Recently formed wind slabs will begin to settle as snowfall becomes showery and winds become calm. But these slabs formed over slick crusts in many locations, and in some sheltered locations, weak snow overlaying the Valentine's Day crust was buried. Therefore, it may take some time for these slabs to settle and bond with underlying surfaces, and it will remain possible to trigger large avalanches on lee aspects. You can use visual clues such as cornices, blowing snow, or wind textured surfaces to identify wind-affected terrain. You can easily dig down to the Valentine's Day crust with your hand, ski pole, or probe to look at new snow and wind slab depths. Watch for signs of unstable snow, such as shooting cracks or collapsing. If you find deep drifts of snow, snow that slides easily off the underlying surface, or see cracks shooting out in front of your skies, it will be best to steer around steep slopes.

    (12/29/2021)

    Small wind slab off Delancey Ridge on the 29th.

    Photo: Will Govus

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Snowpack tests have indicated that large persistent slab avalanches are still possible on shaded slopes above 5,000ft. New snow and wind will test these weak layers, and a shallow wind slab could step down, resulting in a larger and surprising avalanche. So enter new terrain slowly on Monday and consider avoiding shallow, rocky, or very steep unsupported slopes on northern aspects where this snowpack structure likely exists. Persistent slab problems can be tricky and become more sensitive after additional loading. So avoidance of slopes where we know the recipe exists for these avalanches is really the only way to be sure to stay safe, even though chances of triggering one of these may be low. 

    Indicators of persistent slabs are whumphing collapses and snowpack tests that pop or drop suddenly. You can dig down and find the late-January weak layers 1-2 feet below the surface. This layer is a combination of weak sugar-like facets sandwiched between two crusts in many areas. Sometimes you'll find weaker snow or old surface hoar above the upper crust. The weak layers are deepest near and west of the Cascade crest and in wind deposited zones. The crusts may be found near the surface in the eastern part of the zone and in wind-scoured areas.

    (2/5/2022)

    A skier triggered avalanche near Maple Pass. Three people were caught, one was carried over 400ft with no injuries. E, 6,600ft

    Photo: NWAC public obs

Avalanche Discussion

Snow and winds will taper off Sunday night through Monday, and temperatures will continue to cool further with overnight lows of 7- 8°F. Cold temperatures will help new snow settle and hopefully preserve soft snow surfaces. You can likely expect extended sun breaks on Monday, and you may be able to trigger wet loose avalanches in very steep terrain on slopes in direct sun. The cold temperatures and partly cloudy skies will also help keep the distribution and extent of any wet loose activity minimal. 

While you are enjoying the refresh of winter, know that existing slick and weak surfaces may not be bonded well to the new snow. The Valentines Day crust is now buried by 8 to 12 inches of snow in sheltered areas and deeper in wind-loaded areas at upper elevations. Observers found weaker snow beneath and sometimes above this thin crust in high, shaded locations during the week. Approach new terrain slowly and cautiously and investigate these shallowly buried interfaces. Quick hand pits are a great way to identify poor bonding with underlying surfaces. 

Last week observers have targeted the late January weak layer. The one thing in common is that most tests produced sudden collapse results. In general, shaded, northerly aspects are still showing the most potential for human triggered avalanches where the crust-facet sandwich is most defined and weakest. The most recent natural avalanche on this layer was a D1.5 on a rocky, unsupported east aspect, near treeline on Porcupine Peak (see photo). On Thursday and Friday, observers got propagating test results with extended columns and moderate force on N and E aspects between 5,700ft and 6,500ft. Last week, observers noted a cornice fall that triggered a large wind slab avalanche in rocky north-facing terrain. On February 5th, a notable avalanche was triggered near Maple Pass on an east aspect, near treeline. The slide likely occurred on the late January PWL and involved 3 people, carrying one over 400ft. Widespread whumpfing, rolling collapses, and remote triggering of avalanches were all common last week, though these direct signs of instability have become less frequent in recent days. The recent warm temperatures have helped the snowpack and late January weak layer gain strength, but the instability continues to linger.

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