Avalanche Forecast for Sunday, December 30, 2018
This information was published 12/30/2018 at 7:15 AM.
The Bottom Line
Yesterday’s snow and wind deposited wind slabs in isolated areas and behind or below specific terrain features. Wind slab should be easy to identify and avoid in contrast to the refrozen scoured surfaces that exist in many locations. Terrain which contains these wind slabs has MODERATE avalanche danger. Wind scoured areas of icy, hard snow create conditions prime for long, sliding falls. Evaluate snow and terrain carefully to identify and avoid these hazards. Equipment to perform avalanche rescue as well as crampons and an ice axe should be included in today’s kit.
Friday morning brought two inches of snow to our highest elevations that was followed by a half inch of rain in the afternoon. Lower elevations saw the changeover to rain sooner, with higher rainfalls totals and less snow. After an overnight lull, precipitation resumed Saturday morning as temperatures dropped. The summits received all snow (2.1”) with a trace at Gray Knob and at Hermit Lake. At 6am this morning, skies are overcast, north wind is blowing 20 mph and the air temperature is 6F. Today, temperatures will climb to 10F with wind shifting to the north and increasing to 30-45 mph, and some mid and high level clouds passing the region. Monday will start similar to today, though New Year’s Eve celebrations will involve significant snowfall on the summits with rain likely at lower elevations.
Primary Avalanche Problem – Wind Slab
High wind speeds transported the two inches of snow that fell on the summit yesterday into areas of wind slab in lee locations of a NW wind. This wind slab is likely stubborn to human triggers, though specific locations may harbor wind slab close to a foot thick. You may be able to avoid today’s avalanche problem by staying on scoured surfaces, but some pinch points of gullies or narrow slopes may hold wall to wall wind slab.
What is a Windslab Avalanche?
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Two inches of snow fell at higher elevations as our snowpack was refreezing on Saturday. This snow arrived on NW wind around 80mph. Wind of this magnitude likely transported most available snow onto slopes in the lee of NW or into the trees. Traveling surfaces today will be areas of wind slab mixed with wind scoured crusts. Remember that hard wind slabs that are present today may not release or fail in response to the first skier or rider. Traveling one at a time across suspect slopes will be key to safe travel today.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. If you’re in the greater Boston area in a week (January 8) be sure to head to Arc’teryx Boston for evening avalanche awareness presentation with Ryan Matz.
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.
Posted 12/30/2018 at 7:15 AM.
USDA Forest Service
White Mountain National Forest