Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
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In sintesi

Continue to tip-toe around all terrain connected to large steep wind-loaded slopes.  As temperatures rise this week, don't linger below slopes with large overhanging cornices.  If you experience whumpfs or collaspes in lower angle terrain,  make sure to avoid nearby steep slopes at any elevation. 

Problemi valanghivi

  • Persistent Slabs

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

    The potential for surprising and dangerous persistent slab avalanches should continue to shape your travel decisions.  You may trigger these avalanches on steep slopes as well as unusual places far away from typical start zones.  Deeper and more consequential slabs are more likely to be found on lee slopes near the Cascade crest and near and above treeline where westerly winds have recently been drifting snow.  Minimize your exposure to large avalanche paths and look for safe locations to stop or regroup.  Choose simpler and less wind-loaded terrain until conditions change. 

    "Red flag" signs of the danger include whumpfing collapses, cracks shooting through the snow, and tests that propagate or fail suddenly.  You can dig down and find the culprit, the late-January weak layer, 1.5-2 feet below the surface.  This layer may present as a combination of weak sugar-like facets and crusts depending on your location and aspect in the range.  Below 5,600ft you may find buried surface hoar at this interface. We have good information about the problem near Washington Pass, Rainy Pass and Hart's Pass. Further east in the zone, a similar weak upper snowpack structure likely exists but the slabs resting above the persistent weak layer are probably thinner. See or hear something?  Let us know.  

    (2/4/2022)

    A party remotely triggered avalanche (R4-D1.5) from 600 feet away in the Hart's Pass area. This avalanche sympathetically triggered another small slide nearby. East, 6,800ft.

    Photo: Josh Cole

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Numerous wind slabs were triggered over the weekend and yet another round of moderate to strong W-NW ridgeline winds are forecast overnight and for much of Wednesday.   You can avoid triggering these smaller avalanches by steering around new and recent drifts.  Unfortunately, there's significant overlap with the larger and more deadly persistent slab avalanche problem on many of the same slopes. Generally avoid steep open slopes where you see or find wind-stiffened snow, sculpted snow surfaces, and below terrain with large overhanging cornices, 

     

    (2/5/2022)

    Westerly winds transported snow and formed wind slabs and cornices on Cutthroat Pass on Feb 5th.

    Photo: Drew Lovell

Avalanche Discussion

There are no signs that things are changing for the better. More whumpfing and one large rolling collapse was noted by professionals in lower angle terrain near Washington Pass Tuesday.  NWAC forecasters on Monday also found a touchy snowpack in the Silverstar area at low, mid, and upper elevations.  On Sunday, guides near Hart's Pass reported numerous natural persistent slab avalanches on leeward sides of ridges, large collapses, (traveling up to 600ft), and tests showing propagation on the late January weak layer on northwest and east aspects near treeline. For the past week, observers have reported similar signs of instability and tests showing the potential for triggering slides on the late January facet/crust layer throughout the Highway 20 corridor including in the Hairpin Valley and on Kangaroo Ridge. 

While not the top concern, wet loose avalanches will become increasingly likely this week as freezing levels and mid/upper temperatures rise.  On Wednesday, wet loose avalanches should be small and confined to very steep southerly slopes or terrain below cliff bands.

Avalanche observations: On Saturday, a party of backcountry travelers triggered a 3-foot deep slab avalanche near Maple Pass on an east aspect at 6,600ft. Three of the four riders were involved with the avalanche and one was carried 400 vertical feet, but unharmed. See the photo below.  Elsewhere, professionals intentionally triggered small wind slab avalanches on east through south aspects above treeline. Observers reported natural wind slab avalanches in the Hairpin Valley and on an east aspect, near treeline on Cutthroat peak. On Friday, observers remotely triggered a slab avalanche (size R4-D1.5) from approximately 600ft away on an east aspect near 6,800ft in the Hart's Pass areas. This slide triggered another (sympathetic) small slab avalanche. The neighboring West North zone was also active over the weekend, with backcountry travelers triggering both wind slabs and large persistent slab avalanches (see photo below) on the same late-January weak layer that exists in this zone. 

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