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

Northerly winds over the past few days have built wind slabs and affected snow surfaces at upper elevations.  Continue to let the low likelihood, high consequence of a deep persistent slab avalanche shape your travel choices in larger terrain.  

Avalanche problems

  • Wind Slabs

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

    Over the last few days northerly winds have built shallow slabs below ridgelines and sculpted snow surfaces at higher elevations. Use caution on slopes steeper than 35 degrees, especially on the leeward side of ridges or on slopes with wind textured snow.  Steer around convex rollovers and unsupported slopes above treeline.

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

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–3

    We are almost a week past a major avalanche cycle and several days out from a single but very large human-triggered avalanche that likely failed on a deep persistent weak layer.  It's unlikely you'll trigger an avalanche on this layer 3-5' below the surface or observe obvious new signs of instability but the consequences of triggering a deep persistent avalanche remain severe.  

    Monday will be a transition day before cooler weather arrives.  Loose wet avalanches are less likely Monday, but continue to limit your exposure to bigger terrain with large overhanging cornices.  A large natural trigger like corncie fall could trigger a very large and deadly slide. 

    Avalanches have failed on a layer of facets sandwiched between crusts (late January facet/crust combo) inconsistently since early February.  Currently, the weak layer interface is 3-5ft deep in much of the zone. Sudden or propagating results in snowpack tests can help you identify the layer of concern. Further to the east of Washington Pass, this interface is closer to the surface and not far below the most recent storm interface from Feb 26th.  The area around Harts Pass and east may harbor a snowpack most conducive for these slides. 

    (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

Avalanche Discussion

Professionals noted a few touchy and shallow wind slabs on Sunday.  These could be found below ridgelines at upper elevations west of Washington Pass.  

The snowpack continues to adjust following a significant atmospheric river event from 2/27-3/1.  Several feet of snow fell (3" of water at Washington Pass) over this cycle, with rain pushing up to around 6500'.  A widespread avalanche cycle occurred over this period with many large and some very large avalanches observed over the following days.  Surface conditions are a mixed bag with plenty of avalanche debris in paths, a few inches of recent snow above a refreezing crust below 6-6500', and sun and wind affected surfaces in higher and more exposed terrain. 

It's unclear how many avalanches may have released down to the late Jan facet/crust combo during the storm cycle.  However, on Thursday 3/3,  a snowmobile triggered a deep slab. 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 and likley 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 these layers 2-3ft down near Washington Pass. 

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