Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Winds transported feet of heavy, dense snow into upper elevation start zones where you can still trigger a very large slab on a steep or unsupported slope. At middle elevations, nearly 4" of water continues to drain the snowpack. Before traveling on slopes 35 degrees and steeper, ensure there is no free-flowing water above a stout crust.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    We can assume that several feet of heavy, dense snow fell above 7000 ft on Mt Hood. Moderate WSW winds with strong gusts redistributed that snow into a variety of upper-elevation start zones. This snow arrived rapidly and formed slabs that will remain unstable for several days after the storm. A backcountry traveler or the forecast light to moderate W winds through the day on Monday could be the necessary trigger for such an avalanche. If you go into exposed upper-elevation terrain, don't try to nuance this problem, given that slabs given the very large size. Choose lower angle slopes that aren't exposed to overhead hazard, or stick to wind-scoured aspects where you can easily feel a crust under shallower recent snow. Shooting cracks or whumphs may serve as your final reminder to avoid wind-loaded slopes steeper than 35 degrees. Remember to give these upper elevation start zones extra space if you are exposed while traveling on slopes far below.

    Example: Multiple large (up to D2.5) slab releases with 1-4 ft crowns in Mt Hood Meadows A-zone. 

    Photo: Mt Hood Meadows Pro Patrol

  • Wet Slabs

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

    4" of liquid water may or may not drain quickly through the middle elevation snowpacks on Mt Hood.  The uncertainty has us treading cautiously before entering larger open slopes steeper than 35 degrees. Before entering such features, dig down to the 12/6 crust and look for free water running through the rounded grains just above the crust.  A lack of free water gives you more confidence that wet slabs have run their course. While you're examining the upper snowpack, note the depth of the snow above the 12/6 crust. If the slab is more than 6" deep, an avalanche could be large. You can also trigger wet loose avalanches on similar slopes steeper than 35 degrees if the surface snow is saturated and lacks a protective crust. We expect that most of the free water has drained the snowpack, but if you find otherwise, the danger may be higher than forecast and the problem may be widespread.

    Example: A wet slab over a shallow early-season snowpack.

    Photo: Katie Warren

Avalanche Discussion

Mt Hood's snowpack lower and middle elevation snowpack has taken a serious hit from 3 atmospheric rivers in less than 10 days.  Mt Hood Meadows Pro Patrol reported rivers of water incising to the ground with the snowpack compressed to 5-15" at the base of the ski area. With plenty of terrain anchors lower elevations, avalanches will be limited in size with an increased likelihood of injury due to shallow coverage. We're more concerned about wet avalanche activity as you move into middle-elevation terrain. At upper elevations (between 6500 and 7000 ft), you'll find a relatively rapid transition from wet and fully saturated snowpacks to full-on winter. Plan for this transition and a rapid increase in avalanche size that could threaten slopes below.

A foot of new snow that fell Thursday and Friday consolidated into a firm and breakable 8" layer by Saturday and further consolidation by Sunday. Saturated wet snow will be deepest and most dangerous in the upper reaches of the middle elevation band. A decrease in precipitation rates along with gradually cooling temperatures Sunday and Monday should help allow the snowpack to drain and gradually dry out. Give this process the time that it needs.

The last time we had good eyes on middle and upper elevation terrain was on Friday, before the atmospheric river event: The middle elevation upper snowpack looks very different now than the low-density snow and soft wind slabs that Joe encountered in Heather Canyon. You can find photos of this tour in the gallery.

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