Bollettino valanghe

Presidential Range

Mount Washington Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Triggering an large, hard slab avalanche remains possible on steep slopes near and above treeline that were exposed to extreme winds this week.  These hard slabs often appear to be smooth pillow shaped drifts of snow. Additionally, areas of softer and more reactive snow can be found in wind sheltered terrain that was less exposed to high winds. These areas are more capable of producing an avalanche from a human trigger.  You can reduce your risk by sticking to firmer, wind packed snow that isn’t hollow or by seeking out wind sheltered terrain with looser snow. 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.

Avalanche danger will increase after midnight with the oncoming winter storm. 

The Winter Lion Head Route is now the best option to climb to the summit from Pinkham Notch with wind slab avalanche hazards on the summer trail near treeline.

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 is 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, 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

Observations from the Gulf of Slides yesterday: Avalanche classes reported softer snow and observable instabilities in the South Snowfields. Gully #2 is displaying an avalanche crown, likely from the natural avalanche cycle Wednesday - Thursday of last week. It appears that the debris from this avalanche ran up onto the sidewalls, which is not uncommon. The shallow sidewalls of large snow gullies generally make for poor or at least unpredictable “islands of safety” when trying to stay out from the path of an avalanche.  Gully #3 was reported to be “stable enough” by an experienced local mountain guide. 

 

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 all US avalanche fatalities can be found here with details and accident reports appearing as they are submitted to the CAIC. Two more fatalities occurred over the weekend in Colorado including one involving a very large, skier-triggered wind slab. The skier was wearing a deployed airbag, was buried shallowly and skiing alone.

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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