Lawinenlagebericht

Southern Wallowas

Wallowa Avalanche Center
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Lawinengefahr

Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Human-triggered avalanches remain likely on slopes greater than 30 degrees at mid to upper elevations. Reactive storm slabs 12-18" deep are a potential problem on all aspects. Additionally, sensitive wind slabs several feet thick may be present above treeline on NW-N-E aspects. Riders should avoid slopes > 30 degrees where storm totals exceed a foot or more and carefully evaluate each slope for instability. 

This forecast is sponsored by Brooks Painting

Lawinenprobleme

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    The Southern Wallowas above 5500' have picked up 1.5" of water and 12-18" of new snow in the last 48 hours. This new storm snow is not bonding well to the existing variable snow surfaces. These old snow surfaces include slick melt-freeze crusts on southern exposures and surface hoar on more protected slopes at and below treeline. Surface hoar is a notorious persistent and reactive weak layer when buried. If you are hearing the snowpack whoomph underneath you or seeing shooting cracks propogate outwards as you travel, then surface hoar is likely present at the old/new interface. This should have you tucking your tail between your legs and dialing back your terrain choices by keeping off and out from under slopes > 30 degrees. Riders should also avoid potential trigger points in the terrain like convex rollovers and shallow rocky areas in the snowpack, which can be found on windward terrain features mid-slope like ribs and sub-ridges. 

    An additional consideration is the possibility of triggering loose dry avalanches on steep slopes ( >35 degrees) where the new snow lacks the cohesiveness to produce a slab avalanche. The large amount of snow involved and the fast movement of these sluffs downhill could be a potential threat to life and limb. Steer clear of steep slopes where the new snow is overlaying slick crusts, buried surface hoar, and/or the consequences of getting caught could take you into a terrain trap like a gully or tree fence. 

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2

    The 12-18" or more of new storm snow has been easily transported by mostly SW winds and deposited on NW-E facing terrain at and below ridgeline. This will create reactive wind slabs up to several feet thick with human-triggered avalanche likely.  Riders should avoid slopes > 30 degrees where recent signs of wind-loading are evident. This includes areas below cornices and ridgelines on NW - N - E facing aspects and cross-loaded terrain features mid-slope like on the leeside of sub-ridges. Look for smooth pillows with a dabbled texture and if you get any kind of shooting crack or hollow-sounding snowpack underneath you, then skidaddle off and out from underneath avalanche terrain. 

    Winds have been light overnight, however they are forecast to pick up in the afternoon and veer from SW - N - NE - S throughout the day. This may lead to some interesting loading patterns in the alpine. Pay close attention to surface features that indicate wind deposition and expect potential wind slabs in unexpected places. 

Avalanche Discussion

The new storm snow rests on a variable and weak old snow surface. This has likely created instabilities at the old/new interface. Where storm totals are less than 8" or the new snow remains cohesiveless, the main problem will be loose dry avalanches on slopes > 35 degrees. These small avalanches may not bury you, but they could inflict significant bodily harm if they were to take you off your feet or sled and sweep you into obstacles like rocks and trees. Where storm totals exceed 12" there will be a storm slab problem. The best practice for avoiding this problem is to stick to slopes < 30 degrees (i.e. stay out of avalanche terrain). 

A big issue out there is that we had widespread surface hoar formation during the recent dry spell and cold clear nights. Surface hoar is a notorious weak layer when buried. It can propagate fractures for long distances and while you may be on low-angle terrain, those fractures can propagate up onto a steep slope above you and release an avalanche. Not a good situation.  Likely locations for encountering buried surface hoar include more sheltered and protected slopes at and below treeline. If you are hearing the snowpack whoomph underneath you or seeing shooting cracks propogate outwards as you travel, then surface hoar is likely present at the old/new interface. This should have you dialing back your terrain choices and keeping you off and out from under slopes > 30 degrees. 

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