Bollettino valanghe

East Cabinet Mountains

Idaho Panhandle Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

It is possible to trigger avalanches in leeward terrain near ridgelines where wind deposited snow is forming cohesive slabs on north and easterly aspects.  Anticipate these slabs to become thicker and more sensitive by Sunday morning with incoming snow and gusty winds predicted Saturday evening.

Buried weak layers in the upper two feet of the snowpack also remain a concern at treeline and above on north and east aspects. Steep terrain at these locations should be treated with caution.

Problemi valanghivi

  • Persistent Slabs

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

    Buried surface hoar remains present in many locations on north and easterly aspects.  It may be buried over two feet deep in places and while stubborn to trigger this layer is still unpredictable.  Additionally about a foot of snow is sitting on a weak snow interface around the 1/13 rain crust.   In wind loaded locations this "new" snow is forming a cohesive slab and becoming more sensitve to triggering.  Approach convex and rocky terrain with skepticism.

  • Wind Slabs

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

    Winds speeds have been strong enough to entrain available snow and form cohesive slabs near ridgelines and gullys.   The windslab problem is amplified where it rests on or above persistent weak layers.  Expect thicker and more reactive slabs the higher you climb. With incoming weather Saturday evening these wind slabs will become thicker and more reactive by Sunday morning.

Avalanche Discussion

This week we visited the East Cabinets on Monday, West Cabinets on Thursday and took some quick observations from Flatiron on Friday. Snow depth and thickness of layers varies widely across the ranges; but, all of the ranges harbor the "Christmas Crust" and what we are calling the "Lucky Friday Crust" from January 13th. At this time we are finding a pretty cohesive and stable snowpack in most locations. The instabilities are really focused on wind loaded snow near exposed ridgelines and the buried surface hoar on north and east aspects at treeline. North and East aspects in steep terrain should be evaluated closely before committing at this time and will become more of a concern moving into Sunday.

 In the West Cabinets we were pleased to find about 13 inches of snow on a supportive rain crust formed last weekend (1/13).  Unfortunately the new snow was not well bonded to the crust and a thin freezing rain crust deposited Tuesday night was evident 3-4 inches below the surface.  In sheltered areas snow was not consolidated enough to form a cohesive slab, but where it  is loaded by the wind, slab formation was evident.  The other thing that was evident was the weak interface between the rain crust and snow above.  With more snow forecasted Saturday night, this interface is worth keeping in mind moving into Sunday.  Digging deeper, a layer of buried surface hoar is still intact about two feet down.  It is currently bridged by the 1/13 rain crust and producing inconsistent results in stability tests, with moderate to hard force failures.  An avalanche triggered on this layer would be a high consequence scenario. 

Winds that were strong enough to transport snow and form small slabs accompanied each shot of moisture this past week.  Windslabs are present near ridgelines and gullys at mid elevations and above, but are deepeer and more sensitive the higher you climb.  Sitting above the persistent weaknesses, these windslabs have potential to be larger than expected so conservative terrain management and travel practices may be warranted to manage this problem.  Don't let your guard down as this persistent slab problem evolves. 

 

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