Bollettino valanghe

Presidential Range

Mount Washington Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 7 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Triggering an avalanche in drifted new snow will become increasingly possible as snow accumulates, with avalanche danger rising through the day. Continue to be wary of older hard slabs in steep terrain - many rest on top of weak, sugary snow. Steer around deeper drifts of snow to reduce your chances of triggering an avalanche.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    What and where is it:Light density snow continues today with 1-3 inches expected, and winds shift from southwest to north while increasing. Even with modest new snow, wind transport can quickly build sensitive wind slabs on top of the firm, older snow surface. Expect the most reactive slabs in steep, wind-loaded terrain above 3,000 ft, especially on east-facing and south-facing aspects. Look for soft new wind slabs below ridgelines, and along the sides of terrain features where snow drifts in.Keep in mind that new wind slabs are forming on top of older hard slabs with poor snowpack structure in some locations. If the new slabs become large enough, an avalanche of new snow has the potential to “step down” and trigger a larger, more consequential avalanche in the older snow.How can you recognize it: Watch for fresh drifts of soft snow over a harder base - smooth, rounded pillows that feel different than surrounding firm snow. Active blowing snow, snow plumes off ridgelines, and drifts deeper than boot top are your best clues. Cracking is possible, but thin slabs may give little warning before they move.How can you manage it: Evaluate deep drifts in steep, wind-loaded gullies carefully, especially on east and south aspects. Favor wind-scoured surfaces or areas with shallow new snow on lower-angle terrain, and step into suspect deeper drifts cautiously. If you’re unsure, dig to the old, firm surface and test the new/old interface with quick hand shears. The new wind slabs will be easy to identify. Due to spatial variability, understanding the sensitivity of the deeper snow structure as you travel is nearly impossible. 

Avalanche Discussion

Recent observations ( OBS1, OBS2, OBS3, OBS4) continue to show a generally poor snowpack structure consisting of a supportive bridge of old hard slabs capping a weak, sugary, faceted snow layer below. Stability tests repeatedly demonstrate the older slab can propagate, but so far human activity has not been able to sufficiently stress that weak layer and initiate failure.

Today’s new snow may be able to challenge that concerning snow structure later today and upcoming days with new wind slabs. While this new snow contains limited water content and is not expected to overload the deeper structure on its own, the following is worth keeping in mind—if a wind slab avalanche in the new snow were to step down or “punch through” into the older hard slab in an isolated thin spot, it could produce a much larger, more consequential hard slab avalanche.

We’ve been finding this poor structure with some consistency in eastern ravines at middle elevations, where the key variable is the thickness of the overlying hard slab. Observations show it can vary widely, from roughly 35 cm to about 1 meter, with thinner areas the most plausible locations where a smaller avalanche could have an outsized impact. This spatial variability means it can be very difficult to know where those thin spots exist as you move through the terrain, even over short distances.OBSERVATIONS: Please consider submitting an observation on our website or in the new Avy phone app of what you are seeing in your travels. Submitting an observation hones your skills, informs other users, and improves our forecasts. 

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