Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Dangerous avalanche conditions will continue during a prolonged warm-up.  Stay well out of and away from complex terrain as the day warms.  Shallow avalanches may step down to deeper weaker layers, creating much larger and more powerful avalanches that can travel to lower elevations. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–2.5

    Several large to very large natural persistent slab avalanches were noted by professionals over the last 24hrs.  Things will likely get worse before they get better as we step further into an extended mild stretch. 

    Put a larger buffer of terrain between your group and large start zones or complex avalanche paths above 6,500ft. Use extra caution in areas where you find less than 5 feet of snow on the ground above 6,000ft. Choose smaller, supported slopes and stay well out from under larger features. Signs of instability can be inconsistent, creating a tricky problem that is essentially 'unmanageable.' You might not receive signs of instability before the whole slope fails.  Facets buried throughout February exist over a crust in the top 2-4 feet of the snowpack. There's copious evidence of these layers being the culprits of numerous very large natural avalanches and close calls in the zone. 

    (3/5/2024)

    A very large avalanche was remotely triggered by skiers on 3/2 on Kangaroo Ridge. The crown was ~70-100cm deep, and it ran on a layer of facets (1.0mm) buried in mid-February, just above the 1/31 crust.

    Kangaroo Ridge, Pk 8183, WNW, 7,600ft

    Photo: John Stimberis

  • Loose Wet

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

    As the day warms up, look for the tell-tale signs of increasing wet loose instability like wet surface snow, pinwheels/rollerballs and natural wet loose avalanches.  A poor overnight refreeze followed by warmer temperatures on Friday may break down surface crusts more quickly. 

    Wet loose avalanches can become large at mid and higher elevations where they entrain the recent storm snow, especially in tight features like chutes and gullies.  Move to shadier aspects and lower angle terrain without exposure to overhead hazard like cornices and avoid traveling on or below cliffy slopes in the sun.  Wet loose avalanches or cornice fall could also trigger larger and more deadly persistent slab avalanches on the slopes below. 

    Breezy ridgeline winds may lower the chances or delay wet loose avalanches on some slopes, but it should not change how you approach your travel plans on Friday.    

    (2/22/2024)

    A large natural wet avalanche releasing from steep rocky terrain occurred on February 22nd on Big Kangaroo Peak. SW, 7,800ft

    Photo: Will Govus

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Brisk N-E winds will continue to redistribute recent snowfall near and below ridgelines and may cross-load slopes or build wind slabs in atypical locations.  While most wind slabs will be small, every avalanche problem needs to be wrapped back to the potential for triggering a larger and more deadly persistent slab avalanche on older weaker layers.  Cracking in firm, or wind-textured snow are red-flags to avoid steep lee slopes.  Cornices from the prevailing wind direction may start to erode depending on the strength and duration of alpine winds. 

     

    (3/13/2024)

    Small pockets of reactive wind slab on test slopes. 

    Photo: Joe Dellaporta

Avalanche Discussion

It's been an active few days in the Washington Pass corridor with several large persistent slab avalanches that occurred in the last day or two. Multiple parties noted a large natural avalanche in the Cutthroat drainage on 3/12 that ran approximately 1500'.  This may have been a smaller avalanche that released below cliffs and triggered a larger persistent slab on the slopes below.  Since our storm cycle began on 3/9, the Harts Pass Snotel has picked up about 1.8" of water, with all of that falling as snow at mid and upper elevations.  Several small wind slab avalanches were also noted today as well.  

On March 5th, forecasters visited the site of a remotely triggered (D3) avalanche on Kangaroo Ridge. They found that the avalanche was ~2.5-3 feet deep and ran on a layer of facets buried in mid-February, just above the Jan 31st crust. Tests still produced sudden or propagating results indicating that backcountry travelers could trigger similar avalanches, especially in areas of relatively shallow snowpack. There have been multiple reports of close calls, natural avalanches, and snowpack observations in the Highway 20 corridor that point to the deep, persistent slab problem. Widespread, very large natural avalanches occurred between February 28th and March 3rd. 

Snowpack information is limited outside of the Highway 20 corridor and Harts Pass. Let us know what you find if you get out into the backcountry!

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