Bollettino valanghe

Presidential Range

Mount Washington Avalanche Center
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Pericolo valanghe

Mon
Alta quota
1 · Debole
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Triggering a large avalanche today is possible on steep slopes with smooth pillow shaped drifts of snow. Small, isolated pockets of softer snow may also exist in wind sheltered terrain capable of producing an avalanche from a human trigger. You can reduce your risk by sticking to firm wind packed snow surfaces. If the snow you are on begins to feel “hollow” underneath - your risk is increasing. Evaluate snow and terrain carefully. Avalanche danger today is MODERATE.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    The wind slab avalanche problem today is largely driven by recent high winds creating firm (1F to p) wind slabs that, in some places, are covering layers of softer, weaker snow. These hard slabs will be stubborn to a human trigger in most places, though capable of producing a large avalanche should a skier or climber find the thin spot in the slab, which triggers a slide release on the layer of weaker snow beneath. You can reduce your risk by assessing the snow carefully. Listen and feel for a snow surface that feels like a drum. It may feel hollow beneath. An easy test is to push the handle of a ski pole into the snow feeling for softer snow beneath, or use your hand to dig down and look at the snow structure. Hard snow over soft snow is the problem you are looking for. 

    Keep newly formed wind slabs on your radar. If the morning snow showers produce an inch of new snow, west wind will form wind slabs higher in the terrain and avalanche start zones. The new slabs will be reactive to a human trigger, and potentially act as a trigger for a larger slab avalanche from existing snow lower down on the slopes. Depending on wind speed, direction and available snow, slabs can grow to 5-10 times the depth of snowfall. 

    Reduce your exposure to apron-shaped deposits of snow that accumulate below steep gullies and cliffs. These have a history of growing very large after wind events. These deposits of sloughed snow grow quite large and generally require a heavier trigger, such as a new snow load. But it is wise to assume that you could be the unlucky one to find a weak spot in the slab and be the trigger.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–2

    Continuously cold temperatures and crusts have driven a faceting problem in areas of thinner snowpack. Another small slab that was triggered yesterday outside our forecast area (on a slab of ice in Grafton Notch) is a reminder that this issue still exists, though so far only small avalanches (D1) have occurred on this layer. Natural avalanche activity has occurred at lower elevations over a week ago with reports of whumpfing and collapsing continuing in lower and middle locations with a thinner snowpack. Faceted snow has been observed more locally beneath the hard 157mph crust within our forecast area at 4200’ but is likely to be deeply buried in wind loaded terrain where it is more likely to be bridged over by stiff slabs above.

    You can also find faceted snow around the Christmas rain crust though that layer is much more deeply buried at mid and upper elevations. This problem was identified near the ground at lower & mid elevations with a thinner snowpack. Snowfall or a skier/climber could overload these weak layers, initiating an avalanche in the right conditions. Look and listen for collapsing and whumpfing.

Avalanche Discussion

With the next weather system arriving Monday afternoon, it’s worth thinking about our current snowpack. In general, at mostly mid elevations we have firm wind slabs that are stubborn when considering the impacts from human activity. Upper elevations are mostly wind scoured and hard, though textured from the wind. Softer snow exists at low elevations. At this time, there’s around .75 inches of water available for the storm which may fall as snow or a mix that includes some freezing rain. How all this plays out remains to be determined, and ultimately will depend on temperatures and wind. Avalanche danger will increase Monday afternoon and into Tuesday, and will likely factor in the possibility for a new snow avalanche to act as a trigger for existing slabs and combine to create a larger avalanche than expected from just the total storm snow. 

 

A complete incident analysis and report of the fatal avalanche accident that occured in the Ammonoosuc Ravine on February 1 is available here. There are learning opportunities in the stories of accident reports from our database as well as from across the country. Taking the time to read and honestly reflect on your own behavior in the backcountry is worthwhile.

Information on the recent US avalanche fatalities can be found here with details and accident reports appearing as they are submitted to the CAIC. 

An interview with Simon Trautman of the National Avalanche Center on the recent cluster of fatal avalanche accidents can be found here. 

Your avalanche, snowpack, or weather observations are extremely valuable to the forecasters at MWAC. Help create a more accurate avalanche forecast by submitting your observations here. 

Listen to the weekly MWAC Outreach Podcast provided by Ski The Whites. Discussions include snowpack information, weekend outlook, and general avalanche related info. 

Thursday, February 18 @ 7PM - Avalanche Awareness talk with Pat Scanlan: Stealing from the Ski Guides Toolbox - A Free Zoom Webinar

The Harvard Cabin is open for camping only with no entry allowed inside the cabin. There is no access to the breezeway at HoJos.

Please Remember:

  • Safe travel in avalanche terrain requires training and experience. This forecast is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
  • Avalanche danger may change when actual weather differs from the higher summits forecast.

For more information contact the US Forest Service Snow Rangers, AMC visitor services staff at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or seasonally at the Harvard Cabin (generally December 1 through March 31). The Mount Washington Ski Patrol is also available on spring weekends.

 

 

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