Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

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

Expect a beautiful day, but there's enough uncertainty with the deep snow from last week to keep terrain selection confined to less steep slopes. Deep persistent slabs may still be triggered on north facing slopes, especially in steep unsupported areas, or with large triggers. Wind slabs may break widely on weaker, faceted snow from before the big storm. Loose avalanches may run naturally from very steep, rocky areas in direct sun.

Avalanche problems

  • Loose Wet

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

    Plan to stay out from underneath large, complex terrain while the sun is out on Saturday. Strong sun may warm snow surfaces enough to create loose wet avalanche hazard on steep slopes. Up to 6" of newer snow on a crust could slide easily below 6,000ft, and deeper loose slides could occur above that elevation. Look and listen for fan shaped avalanches coming off steep, cliffy areas. Cornices may also begin to sag and fail in direct sun. 

    (1/26/2022) Example of wet avalanches from Jan 12-22th. SE-NE, Whistler Mtn and Cutthroat Peak Photo: Josh Hirshberg

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2.5–3.5

    Put a wide buffer between where you travel and large, shaded avalanche terrain above 6,000ft. If you hit the trigger point for the persistent weak layer, the resulting avalanche could be destructive and unsurvivable. Large triggers such as cornice falls, snowmobiles, or a group of people close together may initiate a deep avalanche. A fair amount of uncertainty exists with these avalanches at the moment; You could see many people travel over any one slope before the 10th person hits the trigger point and starts a very large avalanche. Conversely, the same slope may not avalanche at all. The area around Harts Pass and east may harbor a snowpack most conducive for these slides. 

    A layer of facets sandwiched between crusts from late January has caused very wide avalanches in somewhat sporadic occurrences since early February. At this point, the layer is from 3-5ft deep in much of the zone and can cause very large slides. After the very large storm load earlier this week, it appears that danger from deeper avalanches may continue a while longer, at least. Sudden or propagating results in snowpack tests can help you identify the layer of concern. Further east it's closer to the surface, and not far below the most recent storm interface from Feb 26th. 

    (3/3/2022)

    A very large (D2.5) and widely propagating slab avalanche was triggered by a snowmobile on March 3rd. The crown is estimated at roughly 5ft deep. 6600-6800ft, NE, near Harts Pass

    Photo: Drew Lovell

  • Wind Slabs

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

    Northerly winds picked up on Thursday and Friday, and created shallow windslabs at higher elevations. Use caution on slopes steeper than 35 degrees, especially on leeward sides of ridges, or with wind textured snow. Steer around convex roll-overs and unsupported slopes above 7,000ft. Wind slabs could propagate wider than expected, as recent deep storm snow still needs time to bond due to an unusually weak new/old interface. 

    (3/3/2022) Wind drifted snow on an exposed W aspect at 7,000ft. Photo: Matt Primomo

Avalanche Discussion

The snowpack is still adjusting to the big storm at the end of February. The storm dropped about 3" of water equivalent containing 55" of snow at Harts Pass, and the snowpack depth rose by 38" at Washington Pass. Warming temperatures during the storm caused rain up to 6,500ft. We're still getting a better idea of the avalanche cycle that occurred, and figuring out where we are in regards to stability trends with the deeply buried persistent weak layer from late January. The biggest indicator that conditions are still dangerous came from a snowmobile triggered deep slab on Thursday. This was a very wide slab avalanche, at least D2.5, at 6600-6800ft, NE, near Harts Pass. The crown was estimated to be 5ft deep probably ran on the late January facets. A few other deep crowns were observed in the Hairpin Valley that may have also run on this late January weak layer.

Another, more recent layer of concern was buried on February 26th. This layer may encompass facets above and below a suncrust on southerly slopes, and surface hoar and or facets on shaded slopes. You could find it 2-3ft down near Washington Pass. 

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