Bollettino valanghe

Northern Wallowas

Wallowa Avalanche Center
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In sintesi

Significant accumulations of new snow accompanied by winds from the south have built wind slabs on NW-E facing slopes near and above the treeline. Heavy snowfall has created sensitive storm slabs near the treeline. You will likely trigger one of these avalanches if you venture onto terrain steeper than 30 degrees. Avoiding avalanche terrain is recommended.

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Problemi valanghivi

  • Wind Slabs

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

    Southerly winds have built wind slabs near and below ridgelines. Wind slabs, 2-3' thick, are likely to be found on slopes facing NW-N-E.  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

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    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 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. 

    (3/2/2024) Intentionally skier triggered D1 storm slab on a 6300' NE slope. 20-30 cm crown. It is a 25' tall rock feature over 35 degrees, an appropriate test slope.

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 (3/1) from sledders in the Southern Wallowas indicate heavy sluffing on N-E facing steep slopes. In the Northern Wallowas, ski guides report (3/1) 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.

In the Northern Wallowas, there are reports of collapsing and recent avalanches. One avalanche reported by a long-time backcountry skier had a crown that wrapped onto Phat Ridge in the Wing Ridge area. Phat Ridge is a common up track. 

In the Western Wallowas (part of the Southern Wallowas forecast zone) ski guides intentionally triggered two small avalanches yesterday (3/2). Both avalanches were on north-facing slopes between 7300 and 7600 (near treeline). You can read the full observation here.

Surface Hoar- When this storm began there was well-developed surface hoar everywhere. This 2/26 layer of surface hoar has been found in the Elkhorns and in the Southern Wallowas. Propagating results were observed in Extended Column Tests on this layer yesterday 50cm down. The Valentine's Day surface hoar was also found yesterday in the Southern Wallowas. While the distribution of these layers is patchy, it does exist and is reactive. This creates uncertainty, you should dig down to look for these layers of surface hoar. If you don't have those snowpack analysis skills you should avoid avalanche terrain where it might live (sheltered northerly slopes steeper than 30 degrees).

Graupel-  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. Storm Slabs were reported failing yesterday on a layer of buried graupel 30cm down. 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 layers of graupel which could be the weak layer for an avalanche.

 

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