Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 5 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Increasing snowfall combined with active wind transport will build increasingly reactive slabs with elevation and as the day progresses. Slabs could bond poorly or run effeciently on a firm, slick crust. Step back from steep, lee slopes as the day progresses and move toward sheltered terrain.

Problemi valanghivi

  • Wind Slabs

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

    A more sizeable storm ramps up overnight through the day on Wednesday with an expected 5-7" of new snow and prime moderate snow transport speeds. These slabs will sit above and 1-4" of snow that fell at middle and upper elevations on Tuesday. The fresh and recent snow could be poorly bonded to a widespread underlying crust, particularly at upper elevations where the crust has been slick. Use small test slopes to evaluate the bond to the crust, the stiffness of the slabs, and density differences that create firm over weak layering. Shooting cracks are your last warning sign that a nearby wind loaded slope is likely to be unstable. Avoid steep lee slopes at upper elevations and steer around pillow-like drifts to the lee of ridgelines at middle elevations. Areas of more intense active and recent wind loading will be most likely to produce avalanches. You can gauge the degree of recent transport by noting the buildup of fresh, sharp cornices. When in doubt, return safely along ridgelines, windward slopes, and seek wind sheltered terrain.

    Example: Cracking in stiff drifted snow is a clear sign of instability.

    Photo: Joe Dellaporta

Avalanche Discussion

Tuesday brought around 0.4" of water equivalent to Mt Hood. With temperatures fluctuating around the freezing mark at ski area bases, this translated into around 2" of snow. At upper elevations, wind loading likely formed isolated, small slabs, but winds were mostly light, so this snow mostly remains available for building fresh wind drifts Tuesday night through Wednesday. Tuesday's snowfall buried a widespread 14" thick 3/31 crust that represents a "new ground" for avalanche activity on Mt Hood. 

In addition to being thick, at higher elevations in particularly it is also slick. On Wednesday, scoured slopes could remain primed for a sliding fall and will require skills to arrest a fall. Meanwhile, nearby slopes could have drifts 2-3 ft thick with significant slab avalanche danger. 

We're coming out of generally low hazard in the Mt Hood zone. The rapid increase in avalanche danger on Wednesday requires a shift in mindset and the willingness to dial back your terrain selection as the degree of snow transport, thickness of slabs, and resulting uncertainty increase. Plan your routes in advance as your typical escape routes might be more limited than normal since the snowpack has shrunk immensely over the past weeks. Expect a plethora of travel hazards at lower and middle elevations due to historically low snow.  Fresh snow is likely to obscure hazards, but not materially change the underlying poor coverage.

Are you heading out?  Let us know what you see by submitting an observation here or on the AvyApp.

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