Bollettino valanghe

East Cabinet Mountains

Idaho Panhandle Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

The warm temperatures and rain from Monday-Tuesday have helped stabilize the snowpack.  The primary concern now is windslab at the upper and mid-elevations. Moderate winds have been out of the South to Southwest the last 24 hours and will change to more westerly Friday and Friday night.  Windslabs are likely to have developed on North to northeast aspects especially in the West Cabinets where snow totals were the highest.  The deeper layers of instability (surface hoar that developed mid-December and facets near the base of the snowpack) are less reactive, but could still be triggered with enough force or in a step-down avalanche.

Problemi valanghivi

  • Wind Slabs

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

    Snow totals from Tuesday-Wednesday's storm vary across the Kootenai zone.  The West Cabinets received up to 11" of snow with 2" SWE while the East Cabinets and Purcells only received 2-5".  Wind slabs are likely to have developed on leeward slopes at mid and upper elevations.  Be wary of windloaded slopes, convex rolls, and cross-loaded gullies when you are out playing in the mountains today. 

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3.5

    The deep persistant slab we've been talking about all season is more stubborn and will take a significant amount of force to cause a failure.  While this scenario is not very likely at this point, our snow pit results yesterday in the East Cabinets led us to conclude that it is still possible to trigger an avalanche in the upper layers of the snowpack which could step-down to the ground or facets near the base of the snowpack.  The consequences of a deep slab avalanche would be catastrophic, so don't forget about this problem and assess the likelihood of this happening where you are skiing and riding before venturing onto slopes above 35°.

Avalanche Discussion

The roller coaster of weather we've had this week is starting to change into a more normal winter pattern.  Conditions are variable across the zone, which has me scratching my head a bit regarding what you might see in the snowpack depending on your location. My primary concern for today is wind slab. We toured into the East Cabinets Thursday and observed a thick rain crust up to 6000'.   The East Cabinets only received 2-4 inches of snow on top of the rain crust and winds appear to have remained light, so windslab was not present where we were.  Where snow totals were higher in the West Cabinets, you are likely to find more windslab at the Upper and mid-elevations.  

Below the rain crust we found a damp snowpack that is bonding well. Our pit was on a N aspect at 5800'.  We were still able to detect multiple layers in the snowpack.  We had several failures with moderate and strong force in compression tests and extended column tests on the surface hoar layer buried 40 cm below the surface.  The facets near the base of the snowpack are still present, but are rounding and bonding.  I am gaining confindence in our snowpack, but I haven't dug enough pits to dismiss these deeper instabilities, so stay vigilant and assess the snowpack where you are skiing and riding.  Please provide observations if you are out in the snow!  All observations help us to get a better feel for conditions across the forest.  

We are providing a free "Introduction to Avalanches" course on January 6th. This class will take place from 5 P.M. to 9 P.M. in Libby at the Kootenai N.F. Supervisors Office. There will be a field course the following day at Flatiron Mountain for backcountry skiers and snowboarders. A field day for snowmobilers will be provided on January 21st at Gem Peak south of Noxon. All are welcome to attend the classroom session regardless of your experience. Contact Ben Bernall for more info @ [email protected] 

 

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