Avalanche forecast

Presidential Range

Mount Washington Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Post-storm winds have been moving snow through the night, creating increased avalanche danger on north, east, and south aspects. Avalanches could happen naturally today as well as from human travel. Firm snow conditions in steep, alpine areas may give a false sense of stability as signs of avalanche danger may not be evident until it is too late.

Avalanche problems

  • Wind Slabs

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

    Expect to find wind slabs that have the potential to propagate long distances and are capable of producing D1 - D2 sized avalanches. Slabs will likely present with a strong-over-weak structure making them reactive to additional weight where the slab is thin but stubborn or harder to trigger where the slab is thick. There are multiple sub-snow surface layers that can act as a slick bed surface for these avalanches and stepping on a thin spot in the slab is a likely trigger. Natural avalanches will be possible through today as northwest winds continue to transport snow and slabs continue to grow.

Avalanche Discussion

About11 inches of snow fell on the Mount Washington summit yesterday, which was a surprising deviation from original forecast snow totals (14 - 21 inches). Nonetheless, there is enough snow to create a significant avalanche problem today on the eastern half of the compass rose. A shifting wind yesterday afternoon and an increase in wind speed today allows wind slabs to build primarily on northeast, east, and southeast aspects, but cross loading and drifting effects may happen on north and south facing terrain. With high wind speeds, the surfaces of these slabs are likely to be hard with little boot penetration, while deeper layers of the slab remain slightly softer from falling on lighter winds. Disturbing the snow near these density changes could allow for weak layer failure, propagation, and an avalanche. Though it may be impossible to identify thin spots in the snowpack, many exposed rocks, ice bulges, and vegetation in the last several weeks make stepping on one likely when traveling in avalanche terrain.

Yesterday, storm snow in low elevation steep terrain was reactive to human triggers. Even though snow depths at lower elevations remain shallow, there is still a possibility for small avalanche activity in isolated areas. Small sections of popular ice climbs from around the area could meet this criteria and depending on the amount of snow, extra protection or terrain avoidance should be considered.

We have had limited field observations since our storm yesterday. One of the main questions we still have revolves around how much snow is available for transport onto our easterly aspects. This depends on the outcome of yesterday’s loading patterns, distribution, and density of new snow. We expect our picture to become clearer today as we investigate the questions we still have. Any observations you have are greatly appreciated and helpful to us!

The Lion Head Summer Trail is now closed for the season due to avalanche risk. The Lion Head Winter Route is the preferred option to the summit.

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