Bulletin d’avalanche

Presidential Range

Mount Washington Avalanche Center
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Danger d’avalanche

Thu
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré last year. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

You could trigger a large avalanche in wind-drifted snow on steep east, and south-facing slopes above 3000 feet today. To reduce your risk, steer clear of slopes with obvious drifts and where the wind has stiffened and smoothed the snow surface. Limit your time underneath steep, connected snow slopes to reduce your exposure to natural avalanches.

Problèmes avalancheux

  • Wind Slabs

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

    What and where is it:

    Lookout for newly formed wind slabs today on steep east and south-facing slopes above 3000 feet. These could be stiffer in areas with more wind effect, and in wind sheltered areas like below ridgelines, underneath cliffs, and in narrow gullies could have softer slab characteristics. Initial snow fell with little to no wind, so you are likely to find strong-over-weak structure from new slabs on top of soft, cohesionless snow, which is on top of a firm refrozen old snow surface.

    How can you recognize it: 

    Identify wind slabs as areas of bright white and rounded snow that will be in contrast to old refrozen snow surfaces and could be 30 inches thick. Dense snow drifts deeper than your boot tops, shooting cracks from under your feet, and blowing snow from ridgelines are signs of wind slabs. Use your hand, a ski pole to probe, or a shovel to assess slab depth and the interface of how the new snow is interacting with the old snow beneath it.

    How can you manage it:

    With clearing visibility today, actively look for areas of newly drifted snow. Choose to travel on firm old snow surfaces to limit your exposure to new avalanche hazards. Continue to 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 and large wind slabs. If you're unsure about the sensitivity or location of wind slabs, consider taking an alternate route in simpler, low-angle terrain.

Avalanche Discussion

Yesterday, a low-pressure system moved more slowly than initially forecast, which brought a nice surprise of higher snow totals this morning. On the other hand, this snow has fallen with increasing westerly winds, which has elevated the avalanche hazard to considerable today.

Look out for strong-over-weak structure in new wind slabs. This snow initially fell with light winds on a firm old snow surface, this soft cohesionless snow is the weak layer of concern. As wind speeds increased, winds began to transport this light snow and build wind slabs, these slabs are the stronger layer on top. You can identify this structure by digging down to the old snow surface. The depth will help you to understand the size and using informal tests like hand shears or formal column tests will help you to understand the sensitivity.

Natural avalanches are a possibility today, especially if snow is still actively loading. The biggest red flag to look for is blowing snow onto loaded snow slopes. If you encounter this, consider limiting time under well developed snow slopes as paths in most east-facing terrain are large and fully developed. 

Below 3000 feet you are unlikely to encounter an avalanche problem as temperatures at this elevation warmed well above freezing and snow surfaces experienced a lot of settlement.

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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