Bulletin d’avalanche

Northern Wallowas

Wallowa Avalanche Center
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Danger d’avalanche

Fri
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

A significant storm will impact our area mountains for the next 48 hours. Upper elevations in the Southern Wallowas will receive 12-18" of storm snow today. This new snow will be easily transported by strong southerly winds onto leeward terrain features and build reactive wind slabs 1-3' deep on NW-N-E aspects near ridgeline and cross-load ribs and gullies mid-slope. Avoid slopes >30 degrees with recent wind deposit and watch for storm slab avalanches on steep >35 degree terrain.

Today's forecast is sponsored by The Avalanche Hour Podcast

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Problèmes avalancheux

  • Wind Slabs

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

    Overnight the wind at 7500' has been mostly calm. Today, however, with the approaching warm front, winds will pick up steadily and by early afternoon will be in the 20's gusting 30's out of the south. The 12-18" of new snow forecasted for today in the Southern Wallowas will be easily transported by the wind. Expect to find increasingly reactive 1-3' wind slabs on steep (>35 degree) on NW-N-E aspects near ridgeline and on cross-loaded terrain features mid-slope. Look for smooth rounded pillows below ridgeline and on the leeward side of ribs and gully features mid-slope. The strong winds will move the light density snow farther down the slope than you'd usually expect. It is best for the next few days to avoid steep alpine terrain where reactive wind slabs may lurk.

    Check out the WAC forecaster report from Wing Ridge yesterday.

    (3/8/2023)

    On a small test slope I was able to easily trigger pockets of wind slab by breaking off sections of cornice. One of these set off a sympathetic wind slab that ran underneath the cornice for about 20 yards. The wind slabs were about 12" deep. N aspect @ 8000'

    Photo: M. Hatch

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    The 12-18" of new snow in the forecast for today will likely not bond well to the underlying snow surface, especially to steep southerly aspects that harbor slick melt-freeze crusts or slopes that have been wind scoured. It will be wise to avoid steep (>35 degree) terrain and possible trigger points, like convex rolls and unsupported slopes, where triggering a storm slab will get the new snow moving quickly down the slope, taking you off your feet or sled, and pushing you into terrain traps or stationary obstacles. This avalanche problem will increase throughout the day and tomorrow.

Avalanche Discussion

Protected and Sheltered Slopes Below Treeline

The snow quality on more protected and sheltered terrain is incredible right now. The cold temperatures and constant scud storms have left a foot or more of lovely light density snow in the Southern Wallowa mountains. An additional 12-18" is forecasted for today. Below treeline is the place to find the best snow quality and stability. There really isn't a good reason to go above treeline - you'll likely be punished by the wind and greatly increase your exposure to unstable conditions.

Storm Slab

The Southern Wallowas are forecast to receive upwards of 2-3' of new snow and 2" water by Saturday morning. Snow does not respond well to rapid change. Getting feet of new snow in such a short period of time will create unstable conditions. The avalanche hazard will increase sharply throughout the day and recreationists are encouraged to avoid and stay out from underneath slopes >30 degrees where snow totals surpass 12" or more in a 24-hour period.  Expect the avalanche danger to remain elevated through the weekend. Conservative route selection and travel protocols are a must.

Cornice Fall

In my travels into the alpine in the Northern Wallowas yesterday, I found significant build-up of cornices at and near ridgeline. On small test slopes I was able to easily trigger cornice fall and 12" thick wind slabs on the slopes below the cornices. As yesterday marked the seven year anniversary of the death of our dear friend Kip Rand from a cornice fall on Chief Joseph Mountain, it is important to remember to give overhanging cornices wide berth. Make sure you are on terra firma - look for trees and exposed rocks along with staying on the windward side of ridges.

 

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