Bollettino valanghe

Presidential Range

Mount Washington Avalanche Center
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Pericolo valanghe

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

Isolated, wind-sheltered areas on steep slopes may contain slabs which are reactive to a skier or climber. Be cautious where firm-over-hollow-sounding snow exists. These slabs are most likely to be found beneath the ice across the Headwall in Tuckerman Ravine or beneath the rollover and ice bulge in Main Gully in the Gulf of Slides. Pillow-shaped slabs are likely to be stubborn in most areas but may be more sensitive to a human trigger on foot or ski around specific terrain features like convex rolls, or slabs of ice or rock, or even a thin spot over softer snow. Natural avalanches are unlikely today, though triggering a large avalanche is possible in isolated areas. Pockets of softer, more reactive slabs may exist in lower elevation areas. Evaluate snow and terrain carefully. Avalanche danger is MODERATE on steep, wind loaded areas.

Problemi valanghivi

  • Wind Slabs

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

    These west-north westerly winds reached hurricane force, building firm wind slabs from 1F to P hardness. The most recent snowfall earlier in the week was very low density and transported easily. You can find softer drifts at treeline and in well protected areas. Harder slabs exist in more wind exposed areas where snow has loaded into direct lee terrain features and cross loaded onto others. The larger, firmer slabs are much more stubborn to a human trigger but could be on the larger side if triggered (D2.5). Use the terrain to your advantage when travelling to avoid likely trigger points such as thin spots near the edge of a slab or near rocks. Assess these slabs carefully for signs of instability such as cracking, collapsing or a drum-like surface that indicates softer, weaker snow beneath. 

    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. Smaller and more reactive slabs may be tucked into more wind sheltered locations in the terrain and on steep, narrow drainages at mid elevations. Representative areas on the buttress between Left Gully and the Chute were observed to contain softer and more reactive slabs yesterday.

    These avalanches most occurred as northwest winds increased Thursday night. 1-2" of low density snow fell at higher elevations prior to this increase in wind. The resulting natural avalanche from Chute could have easily buried a person (D2). The bed surface is most likely the 157 mph surface that developed January 24th. Snow hasn't adhered well to that smooth, hard surface.

  • 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.

    This most recent example of faceted snow failing came from Grafton Notch in Maine. You can find faceted snow near crusts in some middle elevations but it has not been reactive in avalanche terrain there. It's worth looking at and keeping in the back of your mind.

Avalanche Discussion

Stubborn wind slabs were tested to some degree yesterday and the bridging power and strength of the wind slabs carried the load without incident. Recent avalanches in Chute and the left side of Center Bowl that most likely occurred during peak wind speeds over Thursday night served a caution flag for folks in Tuckerman Ravine yesterday. Some soft snow was available in a few areas but conditions were generally firm and technical but mostly smooth. The bed surface of the recent avalanche in Chute (6-16” thick by 100’ wide) appears to be the 157 mph slab. No debris was apparent under Lip and Center Bowl and likely would be since debris piles from the small avalanches from the gully just right of Chute and the left side of Center Bowl was pretty obvious on the ravine floor. Right Gully and Lobster Claw coverage has improved significantly. 

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. 

Thanks to everyone for the great observations. The recent reports of faceting around the range have been very helpful. Please keep them coming.  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 and available on Spotify. 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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