Avalanche Advisory for Thursday, February 19, 2015

This advisory expires tonight at 12:00 midnight.

All forecast areas of Tuckerman and Huntington Ravine have HIGH avalanche danger. Natural avalanches are likely and human-triggered avalanches are very likely. Very dangerous avalanche conditions today. Travel in avalanche terrain including the floor of the Ravines is not recommended. The only exceptions to these ratings are the Lower Snowfields and the Little Headwall. The Lower Snowfields has Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. The Little Headwall has Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible.

AVALANCHE PROBLEM: Dry loose avalanches are your first concern right now in both ravines. Wind slab avalanches will begin to threaten travelers in our terrain and grow in size and likelihood through the day and into the night as winds increase and shift to the northwest through the west.  These wind slabs could bury a person and will grow more destructive through the day as wind speeds increase and transport snow into slopes and gullies with an easterly aspect. Older, deeper wind slabs in the Center Bowl and Lip area could play a role in generating a large avalanche if the new slab weight or moving debris exceeds the load carrying capacity of the underlying slab.

WEATHER: A variable thickness blanket of ultra low density snow covers the area with 35.5cm (14″) recorded this morning at Hermit Lake but only 4.6″ (12cm) collected on the summit in low winds. Pinkham recorded 11″ (28cm). These variable totals are not surprising given the nature of this small, but relatively intense system. Light wind is currently blowing out of the SSW in the 20 mph range on the summit but is going to ramp up in speed and, by 2-3pm, is expected to hit 40 mph or so while shifting W to NW. Wind speeds will continue to climb to the 40-55 mph range with gusts to 65 mph by sunset.

SNOWPACK: The kind of champagne powder that blankets Pinkham Notch and Hermit Lake would be ideal for magazine photo shoots for skiing in Utah. Beth’s sample of 14″ from the Hermit Lake snow plot was 3.5%! Sadly, much of this light snow is sitting on a very firm wind hammered surface in steep terrain and would most likely be raked off easily. The new layer of light snow will also form a soft, fist (F) hardness weak layer on which firmer wind slabs will build later in the day. Plumes of snow are already visible coming off of Boott Spur and over Dodge’s Drop. Expect today’s wind slabs to be touchy. By tomorrow, winds approaching 100 mph will change everything.

The variation in snowfall totals lends some uncertainty as to the timing our ratings today. Also, the size and destructive power of the wind slabs will depend alot on the amount of snow available to be transported into the Ravines. With all the recent snow smoothing out and filling in the rocks and broccoli forests at and above treeline, coupled with the ridiculously low densities, make us believe that there will be plenty of snow to generate dangerous avalanches in both Ravines today.

Please Remember:

  • Safe travel in avalanche terrain requires training and experience. This advisory 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.
  • Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast.
  • For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin.
  • Posted 8:30 a.m. February 19, 2015. A new advisory will be issued tomorrow.

Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2713

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