Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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In sintesi

The most likely avalanche problem you'll find are wind slabs above treeline or loose wet avalanches on very steep sunny slopes.  However, tread carefully in and below terrain where deep avalanches have released over the last week.  A large trigger like cornice fall or a smaller avalanche could release a very large and unsurvivable avalanche. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Northerly winds continue to move snow 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 treeline. 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

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Will we see a widespread loose wet cycle?  It's unclear, but slightly warmer temperatures on Sunday and sunshine should keep you on your toes.  Loose wet avalanches may become large on steep sunny slopes at higher elevations where they could gouge down into older layers.  At lower elevations, they'll be smaller but may run further than you expect above a crust.  Pay attention to the terrain above you and don’t linger under steep slopes basking in the sun.  As we inch closer to the spring equinox with a higher sun angle and longer days,  we'll start to expand the compass regarding loose wet avalanches. 

    Continue to be wary of slopes with large overhanging cornices. You'll want to avoid lingering in terrain where a cornice fall could trigger a deeper and more deadly avalanche.

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

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2.5–3.5

    We're in a strange uncomfortable spot, several days from a major cycle and a few days out from a single but very large human triggered avalanche 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 would be severe.  Our best advice is to continue limiting your time in and near avalanche terrain above 6,000ft and be mindful of the overlapping avalanche problems possible on Sunday.  The area around Harts Pass and east may harbor a snowpack most conducive for these slides. 

    Much of the below treeline elevation band will fall under Low danger, but due to overlapping avalanche problems and the potential for very large avalanches that could run far distances and below treeline, the avalanche danger will be listed as Moderate.

    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. 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

Avalanche Discussion

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 recent 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 it 2-3ft down near Washington Pass. 

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