Avalanche Advisory for Tuesday March 17th, 2015

This advisory expires at midnight.

Tuckerman and Huntington Ravines will have Considerable avalanche danger.  Natural avalanches will be possible and human triggered avalanches will be likely.  Dangerous avalanche conditions will exist requiring conservative decision making.  The Little Headwall has Low avalanche danger.  Natural and human triggered avalanches are unlikely except in isolated terrain.

AVALANCHE PROBLEM: Wind Slabs are the primary concern today.   Unstable slabs left over from the weekend storm still exist, peppered across the Ravines.  This morning we are starting out with old wind slabs having fair to good stability depending on location.  Moderate winds early this morning will cause the start of new loading to occur.  This will begin with lower density soft slabs, moving towards denser slabs over initial layers as the day progresses.  Raging wind velocities, perhaps climbing to 130mph (210kph) late today, will move a tremendous amount of snow.  This will create a period of natural avalanche potential in both Ravines. As winds move through the century mark a number of locations will move towards scouring and stabilizing.  Peak instability will likely be through the midafternoon towards dinner time, but this will depend on how quickly wind speeds increase.

WEATHER: A somewhat tranquil morning will create what some call a “sucker hole”.  Drawing in the unaware tempting them to skip through the mountains.  However, as the day progresses the current summit temperature of 23F (-5C) and a wind speed of 31mph (50kph) will seem like another world. Big wind will rule by this afternoon eventually gusting way over 100mph (160kph).  This evening a peak velocity may reach between 130-140mph (210-226kph) as temperatures fall to -20F (-29C).  What’s that in wind chill? Too cold!  Snow is expected up to 2” (5cm) today and again tonight, with some localized higher amounts due to a developing trough.

SNOWPACK: The wind slabs that were created during the weekend storm still hold some instabilities as we head into the next loading event today.  Two human triggered avalanches over the past couple of days were good indicators of the reactivity to skier weight and loading.  Solar gain helped some direct south facing slopes stabilize a bit yesterday, although nearby snow pointing slightly towards SE or SW retained their cold properties and was less affected.  Today, a building wind will likely create an upside down snow pack with light low density snow developing this morning, followed by denser layers through the day.  As the freight train winds move snow from the alpine zone and the other side of the range, particles will become smaller, beat up, and will pack into denser slabs.  This scenario develops a classic instability of dense harder snow over newly developed softer slabs, leaning towards a propensity to fracture and fail.  The timing of the developing wind ramp up is the key ingredient to this recipe.  Forecast models are showing a shifting wind from the W to the NW up to 50mph (80kph) this morning, 50-70mph (80-112kph) during the early afternoon, climbing towards 100 late in the afternoon, gusting much higher.  By late today into the evening 110, 120, 130, 140mph are all a possibility so expect treeline travel to be less than inviting.  If tonight’s conditions were a high school band they’d be billed as “Extreme Insanity”.  Be conservative in your travels and plan to get out of alpine zones early today.  Although it seems fine now, it won’t be later.  These winds will eventually scour many slopes turning them back towards more stability.  This may occur as early as later this afternoon for Huntington Ravine, but between poor climbing weather and occurring late in the day this won’t be too helpful for mountain travelers 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 8:40 a.m. March 17, 2015. A new advisory will be issued tomorrow.

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