Avalanche forecast

Presidential Range

Mount Washington Avalanche Center
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Avalanche danger

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

Human triggered avalanches may occur in the recently wind-transported snow that lies on the surface of steep east-facing terrain. It could be possible to trigger an unstable pocket of snow in the middle and upper elevations in places less exposed to the wind. Smooth deposits of snow found in steep confining terrain should be avoided to reduce your risk.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Pockets of wind drifted snow are scattered across the steep slopes of the middle and upper elevations. Eastern aspects have collected the wind transported snow leaving behind slabs of unstable snow in places where winds are sheltered. These slabs can be 1 to 3 feet thick and react brittle or hollow as you step onto them. Some of these isolated pockets are most sensitive where the slabs tapper in thickness, sometimes near rocks and vegetation or abrupt changes in terrain.

    Within these drifted slabs you can find changes in density where shear and mostly planar failures can be found along weak layers with stability testing. Recent observers performing compression and extended column tests have revealed these planes of weakness to be about 10cm down from the surface. Sometimes these changes in snow hardness are from a lull in wind intensity or directional changes, or even from a rapid increase of snow load or changes in grain type. Assess today’s slab stability in multiple locations as you travel, and try to understand their sensitivity to human triggering.

Avalanche Discussion

Recent snow, around 1.5 to 0.5 inches each day for the past 5 days, has created layered slabs of wind transported snow in places less exposed to the wind. In the upper and middle elevation zones you can find places sheltered from the winds influence below ridgelines, in steep confining gullies, and around terrain features where changes in steepness are abrupt. If you trigger one of these wind slab avalanches expect it to release above you and entrain large amounts of packed snow.  

As temperatures decrease to near-arctic conditions this week, realize that both the snowpack and the human body become more fragile. Cold temperatures help pull moisture and bring about a metamorphism within the snowpack that can change the structure of snow grains. Rather than strengthen the snowpack's cohesion, cold & dry weather changes the bonds between snow grains from tightly packed to more loose and weak with poorly bonding properties. Facets are the result of this process, which look like very angular and loosely connected versions of the once mighty flake.  

Some of the mid and upper snowpack layers are going through the facetting process, but wind transported snow can sometimes bridge these weak layers. Bridging occurs when a stronger layer of snow spreads the surface area over a weak layer, making the new strong layer supportable. Faceting can also do the opposite, in that it degrades even further the weak layer past the point of the strong layers supportability, making that old weak layer once again reactive. We will do our best to track these scenarios and keep you informed as they develop. For now, avoiding the surface wind created slabs is the main avalanche problem. 

The Lion Head Summer Trail is CLOSED due to increased avalanche hazard. The Lion Head Winter Route is OPEN and the most direct route to the Mount Washington Summit from Pinkham Notch. 

OBSERVATIONS: Please consider submitting an observation 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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