Bulletin d’avalanche

Southern Wallowas

Wallowa Avalanche Center
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Danger d’avalanche

Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Significant new snow overnight and continuing today will create reactive storm slabs 12-18" deep at mid to upper elevations in the Southern Wallowas today. Additionally, SW winds will transport this new snow onto N-E aspects near ridgeline building sensitive wind slabs up to several feet thick with human-triggered avalanches likely. 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 CB Construction, Inc. 

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Overnight the Southern Wallowas above 5500' picked up about 1" of water and 8-10" of new snow. The zone can expect an additional .6" of water and 6-8" of new snow today. This new storm snow will not bond 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 dialing back your terrain choices and 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 like ribs and sub-ridges. 

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1.5–2

    The 12" or more of new storm snow will be easily transported by SW winds today 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 ribs. Look for smooth pillows with a dabbled texture and if you get any kind of shooting crack or hollow-sounding snowpack underneath you, then make sure you stay off and out from underneath avalanche terrain. 

Avalanche Discussion

The new storm snow is falling on a variable and weak old snow surface. This will create instabilities at the old/new interface. Where storm totals are around 6" or less 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 off and out from under slopes > 30 degrees. 

Régions couvertes