Avalanche forecast

Presidential Range

Mount Washington Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
3 · Considerable
Below
1 · Low
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Highlights

You could trigger a large avalanche in wind-drifted snow on steep north, east, and south-facing slopes above 3000 feet today. South and east-facing terrain are also spots that hold a higher potential of triggering a much larger avalanche deeper in the snowpack. To reduce your risk, steer clear of slopes with obvious drifts and where the wind has stiffened and smoothed the snow surface.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–2.5

    What and where is it:

    Wind slabs formed from 10 inches of light-density snow the past three days and strong west winds may still be sensitive to your weight and span the width of entire slopes or avalanche paths. Triggering a surface 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 slabs, formed from over 40 inches of new snow and high winds over the past 12 days, 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, blowing snow at the ridgelines, 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:

    With good visibility today, actively look for and avoid obvious drifts or slopes where the wind has compacted the snow. 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 wind slabs. If you're unsure about the sensitivity or location of wind slabs, consider taking an alternate route in simpler, low angle terrain.

    Photo: Patrick Scanlan

    Summer Lion Head Traverse is an area where a well connected wind slab spans the entire slope. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–3

    What and where is it:

    Old hard slabs are sitting on a buried layer of weak snow and 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. Large triggers, such as surface avalanches or multiple people on a slope, will increase the odds of impacting these layers deeper in the snowpack. As you move through and around avalanche paths, limit exposure to large, open slopes where persistent slabs are more likely to be more dangerous. Stack the odds in your favor by following safe travel protocols and only expose one person at a time to avalanche hazards.

Avalanche Discussion

Three concerns to keep on your radar today. 

  1. Surface wind slabs:  Snow from Sunday began building wind slabs in the evening and into Monday as winds increased. These slabs were observed to be 1-3 feet thick and continued cold temperatures and decreasing winds today may preserve reactivity.
  2. Persistent Slabs: A persistent weak layer is still present in avalanche terrain. Though recent snow accumulation may have further buried 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 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, a surface 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.

For the month of February, Hermit Lake has recorded 40.5 inches of snow while the Mount Washington Observatory has recorded 25.7 inches. While no single event has been a significant producer, the incremental accumulation of snow this month has been impressive. Alongside this snow has been consistently cold temperatures, which is one of the reasons that the avalanche hazard has remained elevated. In this past storm, winds increased to productively load snow, but there was no high wind event that drove increasing stability into the snowpack. Decreasing winds today will likely preserve some reactivity in the snowpack, which was observed in forecaster field time yesterday. 

It is time to choose terrain wisely, as you have the potential to trigger a large avalanche on well-connected paths that could break deeper in the snowpack. Incremental loading can create surprisingly large avalanches as it is hard to know exactly when there is enough weight to stress layers to fail for natural avalanches, and adding people onto a slope can add additional stress. With no reports of avalanches from this past storm, decreasing winds, and cold temperatures avalanche conditions remain dangerous, and you should take time to actively assess terrain and your confidence in the structure of the snowpack you choose to travel on.

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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