Bollettino valanghe

Presidential Range

Mount Washington Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
1 · Debole
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In sintesi

Recent snow and wind make triggering an avalanche likely in steep, wind-loaded terrain. Smaller avalanches may provide sufficient triggers for much larger, more destructive avalanches. To reduce your risk, steer clear of obvious drifts and slopes where the wind has stiffened the snow surface.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–2.5

    What and where is it:New wind slabs from 6+ inches of light-density snow and slowly increasing wind overnight. These new slabs could be sensitive to your weight and have the potential to avalanche naturally. Triggering a smaller wind slab avalanche has the potential to step down into deeper weak layers and create a much larger and more dangerous avalanche. Keep in mind that larger, more dangerous wind slabs, formed from about 30 inches of new snow and high winds over the past week, are hidden beneath softer new snow on north, east, and south-facing slopes.How can you recognize it: Look for smooth, rounded snow slopes in wind-protected areas where the wind has worked to build new, softer wind slabs. Shooting cracks under your feet, hollow-sounding snow, and deep drifts of softer snow are signs of a wind slab avalanche. It is possible to be traveling on a harder, dangerous wind slab without obvious warning signs. 

    How can you manage it:If visibility is good, actively look for and avoid obvious drifts or slopes where the wind has compacted the snow. If visibility is poor, travel carefully in avalanche terrain, aiming to reduce your exposure and limit the time you spend beneath large, connected snow slopes that may hold dangerous wind slabs. If you're unsure about the sensitivity or location of wind slabs, consider taking an alternate route.

  • Persistent Slabs

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

    What and where is it:Old hard slabs are sitting on a buried layer of weak snow could be triggered by finding a thin spot in the snowpack or by the weight of a smaller avalanche. This poor snowpack structure has been found specifically in the Summit Snowfields, gully entrances on the south face of Tuckerman Ravine, and the south aspects of Huntington Ravine and it likely exists in other similar terrain.  Additionally, on February 4th a very large avalanche on the Gulf on Slides Southern Snowfields stepped down to this layer and the possibility of this happening elsewhere remains. Note that one of the places this avalanche problem exists is just to the north of where the Lion Head Trail leads to Split Rock on the summit cone and on the Summer Lion Head Trail.

    How can you recognize it: Visually, these dense persistent slabs are difficult to spot, as they will appear and feel very stable underfoot. The unlikely nature of this avalanche problem means a slope could be skied multiple times without triggering it, but the unlucky skier who finds a weak spot in the slab may trigger a large avalanche. Don’t rely on tactile red flags, like "whumping," as a warning.

    How can you manage it:Understanding exactly where this problem exists in the terrain will be very challenging. Travel strategically, avoiding high-consequence terrain, and choose conservative terrain decisions. As you move through and around avalanche paths, limit exposure to large, open slopes where persistent slabs are more likely to be more dangerous.

Avalanche Discussion

Three concerns to keep on your radar today. 

  1. New wind slabs.  Snow from overnight Friday has formed new wind slabs. While winds were initially slow yesterday, they’ve picked up today, making conditions ideal for transporting snow from the west to the east-facing slopes. These slabs are expected to be thick and will remain reactive throughout the day due to cold temperatures and moderate winds (for Mount Washington).
  2. Persistent Slabs. The persistent weak layer is still present. Though recent snow accumulation may have protected and bridged the weak layer in some areas, it’s still possible, though unlikely, to trigger a slide if you find a thin spot over the weak layer.
  3. Interaction Between New Wind Slabs and Persistent Slabs: A human skier typically has an impact bubble of about one meter into the snowpack, which is usually insufficient to trigger the deeply buried weak layer we are tracking. However, an avalanche in the new wind slabs could generate a much larger impact bubble, potentially triggering the older persistent slabs and resulting in a much larger and more destructive avalanche.

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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