Avalanche Advisory for Saturday, March 9, 2013

Expires at midnight Friday, 03-09-2013

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. Natural avalanches are possible and human triggered avalanches are likely in the Sluice. Careful snowpack evaluation, cautious route finding and conservative decision making is essential. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The only exception to this is the Little Headwall which has Low avalanche danger. Natural and human triggered avalanches are unlikely there.

Huntington Ravine has MODERATE avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible.

With yesterday’s wind loading and today’s intense solar heating we have a lot of stability issues to consider.  Friday’s peak wind from the ENE hit 80mph (128kph), the highest velocity in 9 days. As we anticipated, snow redistribution did occur from alpine areas but not in the volumes we were expecting. We certainly saw new slabs develop but not in the size and distribution you would predict knowing a foot of snow fell in the same 9 day window.  The unstable air mass created many snow devil whirls and winds blowing from most directions as winds slapped north facing slopes and then came racing across the terrain from the south!  In our field time yesterday afternoon Frank and I found, once again, intense variability in stability and weaknesses without finding a consistent problem. However some common themes emerged.  Many locations had facets on suncrusts, very large chunks of rime from alpine bushes stripped by the wind, and graupel mixed in between.  In steep new pockets of snow within Right Gully and the Sluice we found unstable new thin slabs failing about 15cm down.   Failure occurred on a variety of weaknesses resulting in Compression Test scores of 5 and 6 with much higher ECT scores with no propagation.  Deeper weak layers also resulted in high CT scores with no consistency.  These stability tests were done in locations we knew we would likely find easy failures and doesn’t fairly extrapolate to most locations.  I mention it because it demonstrates the spatial variability we have out there and it’s important to constantly look out for new instabilities as you travel.  These steep areas of weak slabs will likely be the origin for today’s main problem- SOLAR GAIN AND HEATING!

Today is clear, beautiful, and should be the warmest day in a month and a half for treeline locales.  A dropping wind from the N may fall to 10mph (16kph) which will do nothing to keep S facing slopes cool. We expect rapid and intense heating of our newest slabs on S aspects. The Sluice will lead this charge as it has the largest direct S facing slopes with the largest consequence, an avalanche sweeping through Lunch Rocks.  If a wet slab releases in the Sluice it will likely be large and fail initially in its steepest areas.  Trailing behind the Sluice in likelihood and consequences will be its neighbors the Lip and Right Gully. After that in concern is the Lobsterclaw in Tuckerman and Huntington’s Yale, Damnation, and North due to their smaller, narrow nature.

The Bulls-eye points: 

  1. South facing slopes will see intense solar gain and heating. The greatest question will be can the heat weakening find a porous enough pocket of slab, with enough of a weak layer, to cause slope failure?  This is a rare occurrence in our Ravines and a degree of uncertainty exists for us, but these are conditions that can’t be ignored.  The Sluice harbors the greatest risk due to the both likelihood and consequences.  We believe locations facing S under a Moderate forecast have unlikely natural potential, but it is not completely out of the question.  As we move into the afternoon I would expect them to reach the upper end of the Moderate definition.
  2. As you move across Tuckerman you will start reaching colder slabs and I see the Chute and Left Gully on the lower end of Moderate.

 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 8:45am, March, 9th 2013. A new advisory will be issued tomorrow.

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

2013-03-09 Print Version