Avalanche Advisory for Tuesday, December 12, 2017

This advisory expires at Midnight.

Huntington and Tuckerman Ravines have Considerable avalanche danger today. Natural avalanches are possible and human triggered avalanches are likely. Careful snowpack evaluation, cautious route-finding, and conservative decision-making are essential. The only exceptions to this rating are the Little Headwall and Lower Snowfields in Tuckerman Ravine due to lesser development of avalanche paths.

 AVALANCHE PROBLEM: Wind Slab will be our primary avalanche problem. Storm Slab will develop into a secondary problem by the end of the day in areas less affected by wind. Avalanche size and distribution for a Considerable rating includes “Small avalanches in many areas, or large avalanches in specific areas”. Today we expect both. Left Gully and Chute had the greatest avalanche path development prior to the storm Saturday and Sunday and will be loaded by today’s wind direction. Other areas likely filled in significantly in the past several days, developing paths that could produce avalanches today. Despite the recent new snow, many boulders, bushes and cliffs lurk beneath the surface and in many slide paths making a ride in debris particularly dangerous. Today is a good day to go to the resort or climb at lower elevations.

 WEATHER: The Saturday/Sunday storm produced 14” of snow on the summit on Mt. Washington and was followed by consistently strong west wind, loading leeward terrain. Visibility has been limited since then, though we expect leeward terrain of a NW and W winds has seen significant loading and avalanche path development. By dark today, 10” or more new snow is forecast for our terrain with southerly wind around 50 mph. The temperature will rise this afternoon, likely increasing the density of the slab and stressing the soft weak layer below. Snowfall will slacken but continue tonight and tomorrow as wind shifts through W to NW and intensifies by midday tomorrow. Anticipate elevate danger tomorrow in many areas.

SNOWPACK: A switch flipped. Significant snowfall and loading wind speed and direction means that terrain which holds little to no snow 3 days ago could easily produce an avalanche today. The lack of visibility over the same time period means that we’re not certain to what extent avalanche paths have developed.  A layer of wind slab produced by the Saturday/Sunday storm and W to NW winds did avalanche and could still produce an avalanche where it has not already. Today’s significant snowfall and southerly wind will result in a new layer, wind or storm slab depending on location. This layer will likely be reactive to a human trigger. In areas receiving most loading today we expect natural avalanches by the end of the forecast period. The weather will likely keep many out of our terrain today, but anyone venturing into the ravines today should realize the increased likelihood for any developed snow slope to avalanche. This is our first 5-scale advisory of the season. The snowpack is in rapid transition, developing significantly since its minimal state late last week.

The summer Lion Head Trail is the safer route to the summit than trails through Tuckerman and Huntington. The Lion Head Winter Route will open when snow fills in avalanche paths on the summer trail and fills in the winter route enough to cover rocks, mud and bushes. The John Sherburne Ski Trail still lacks a packed base and has very thin cover. It’s getting closer but will remain a dicey ski choice today.

Please Remember:
• Safe travel in avalanche terrain requires training and experience. This bulletin 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 8:15 a.m., Tuesday, December 12, 2017. A new Advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2017-12-12