Bulletin d’avalanche

Northern Wallowas

Wallowa Avalanche Center
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Danger d’avalanche

Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Points saillants

Significant accumulations of new snow have created dangerous avalanche conditions near and above treeline on all aspects. Strong southerly winds have built thick unstable wind slabs on NW through E  facing slopes.  Stay off and out from underneath slopes steeper than 30 degrees. 

This forecast is sponsored by CB Construction.

Problèmes avalancheux

  • Wind Slabs

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

    Southerly winds have built wind slabs near and below ridgelines. Wind slabs, 1-2' thick, are likely to be found on slopes facing NW-N-E.  Human-triggered wind slab avalanches are likely at upper elevations in the Blues on steep slopes. The effects of recent wind-loading may present as smooth hard pillows lurking below ridgelines or sub-ridges mid-slope, as cornices hanging imposingly over steep slopes, or as stiff punchy windboard.  Look for and avoid steep slopes (>30 degrees) with large overhanging cornices, smooth textured wind pillows, and/or deposition zones with convex rollovers. You may find reactive wind slabs at lower elevations. Be cautious around leeward terrain features mid-slope like sub-ridges and gullies. 

    (2/28/2024)

    Crown and debris from a wind slab avalanche in Salt Creek Bowl. D 1.5

    Photo: Nick Burks

  • Storm Slabs

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

     

    The Northern Wallowas have received around 2+" of water and 1-3' of new snow.  Dangerous avalanche conditions exist. Near and above treeline human-triggered avalanches are very likely on slopes > 30 degrees. The best way to avoid triggering a storm slab avalanche is to avoid being on or under avalanche terrain. Practice conservative travel techniques by spreading out and only having one rider on the slope at a time. 

Avalanche Discussion

The storm that began Monday 2/26 has deposited 1-3' of new snow across our forecast zones. This storm has been marked by strong winds out of the SE, S and SW. These winds have moved a lot of snow and built wind slabs on NW through E-facing slopes. Many of these slabs formed on top of a melt-freeze crust. This crust would be an excellent sliding surface for the heavy slab that sits on top of it, all it needs is a trigger. That trigger could be you or the additional weight of the new snow. Avoid traveling on or below wind-loaded slopes.

On slopes not affected by the wind- storm slabs and dry loose avalanches lurk. Reports from sledders in the Southern Wallowas indicate heavy sluffing on N-E facing steep slopes. In the Northern Wallowas,  WAH ski guides report lots of snow moving below the treeline, with storm slabs and dry loose avalanches running on steep unsupported slopes. These observations illuminate a Red Flag, recent avalanches, and tell us we should avoid avalanche terrain until the snow has had time to settle.

Surface Hoar and Graupel. When this storm began there was well-developed surface hoar everywhere. While it appears to have been destroyed before this new snow could bury it intact, it is still a source of uncertainty. This storm has brought a lot of graupel with it. Graupel is small round BB's of snow, it can look like hail. As you can imagine, a layer of BB's isn't very stable. These layers of graupel are another source of uncertainty. When our uncertainty increases, our margins of safety should increase too. Make conservative terrain choices and dig down into the snow to look for buried surface hoar and layers of graupel which could be the weak layer for an avalanche.

Régions couvertes