Avalanche Advisory for Sunday, March 20, 2016

This advisory expires at 12:00 midnight.

Tuckerman Ravine has MODERATE and LOW avalanche danger.  Sluice, Lip, and Chute have Moderate avalanche danger.  Natural avalanches are unlikely but human-triggered avalanches are possible.  All other forecast area have Low avalanche danger.  Natural and human-triggered avalanches are unlikely.  Lobster Claw, Lower Snowfields, and Little Headwall are not posted due to a lack of snow in these areas.

All areas of Huntington Ravine have LOW avalanche danger.  Natural avalanches and human-triggered avalanches are unlikely.

AVALANCHE PROBLEM: Today’s main avalanche problem is Wind Slab.  Snow starting Thursday and continuing into Friday left over six inches on the summit of Mount Washington.  This snow arrived on west winds, followed by a clear but windy day on Saturday.  Thin crown lines in Chute and Center Bowl, likely from Friday and still visible this morning, are clear signs of an unstable layer in the new snow.  The areas of concern today are those which have a smooth layer of new snow with no visible crown lines.  I would thoroughly evaluate Lip and Sluice before venturing into these areas.  Most other areas around both ravines that contain instabilities have old or wind-scoured surfaces that can allow passage around potentially unstable snow.

WEATHER: Cold and windy weather yesterday allowed for little stabilization in the new snow.  Today looks to be clear skies, mild winds, and temperatures reaching the teens, allowing for some rounding of grains to take place, particularly in the weak layer of graupel and rimed crystals.  Clouds will develop tonight and what was looking like a Nor’Easter now looks like a trace to 2” on Monday.

SNOWPACK: Prior to Wednesday, March 16, the snowpack went through several stabilizing events: over 1.3” rain followed by a deep freeze then followed by several corn cycles.  This is removing many concerns about weak layers deep in the snowpack.  The focus for today is the new snow, primarily existing as wind slab, sitting on top.  The snowfall began during warm air temperatures, which allowed it to bond well to the base layer.  Strong west winds blew from Thursday through last night, loading several lee forecast areas.  We’re also finding a significant amount of graupel and heavily rimed particles in the new snow.  The wind slabs tend to be rather touchy due to the poor bonds formed by these particles as well as the fact temperatures have remained cold until today.  I expect bonds might strengthen through the day, but with the degree of spatial variability in play, you may find instabilities very close to the more stable wind-scoured surfaces.

 Other typical spring hazards include:

  • Long sliding falls – Crampons and ice axes are highly recommended in steep terrain. Snowshoes and microspikes are no substitute. Spring weather brings variable snow surface conditions that change by the hour and by aspect. Arresting a fall on an icy 30+ degree slope is practically impossible.
  • Crevasses, moats and waterfall holes – Warm water flowing under the snowpack creates holes and thin spots in surface snow that are deep enough to injure or kill you. New snow can obscure the openings.
  • Falling ice – Colder temperatures are putting this hazard behind others for the weekend.

TRAILS INFO:

  • The Tuckerman Ravine Trail uphill from Pinkham to Hermit Lake is mostly wall-to-wall ice covered with the layer of new snow. Traction devices or crampons are necessary for reasonable travel on this trail.
  • The Lion Head Summer Trail is open. The winter route is now closed.
  • The Sherburne Trail is closed about 2/3 mile up from the parking lot. Please respect the closure by walking over to the Tucks trail at the rope to reduce erosion on the ski trail.

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 8:25a.m., Sunday, March 20, 2016. A new advisory will be issued tomorrow.

Helon Hoffer, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2716

2016-03-20