Avalanche Advisory for Friday 1-27-2012

This advisory expires at midnight Friday 1-27-2012

Tuckerman and Huntington Ravines have HIGH avalanche danger today.  Natural avalanches are likely and human triggered avalanches are very likely.  Very dangerous avalanche conditions exist and travel in avalanche terrain is not recommended. This includes runout paths of avalanche activity such as the fan in Huntington and the floor of Tuckerman Ravine. The Lobster Claw, the Lower Snowfields, and the Little Headwall are not posted due to an overall lack of snow. Forecasts for these locations will begin when conditions warrant.

As expected, we are in the middle of a winter weather maker with about 6” (15cm) on the ground as of 7am. Light snow began just after dark last night and continued through the evening.  Icing has been mixing with new snow beginning to increase densities causing an inverted snowpack giving us stability concerns.  Additionally, loading has occurred from a southerly direction in the 35-45mph (50-72kph)  range over the past 12 hours, this will start shifting and come from the West and increase.  By late in the day wind speeds should be gusting over 60 mph (100kph) from a westerly direction.  Our main concerns through the morning are focused on aspects that have a northern component due to the overnight loading from the South.  As winds shift and increase they will have a larger pickup zone, namely Bigelow Lawn and the Alpine garden, to load the Ravines directly due to their overall Eastern facing direction.  Some cross loading will occur later today on South facing aspects, but locations like the Right Gully in Tuckerman and Damnation and North Gully in Huntington will hit the High rating later than other forecast areas.  Complicating and accelerating today’s instability issues is the transition from snow to….yup…rain.  The summit is expecting a high of about 30F at 6288 and the Conway valley areas are expecting 40-41F early in the afternoon.  There is a good chance we will see rain develop in our primary avalanche terrain between 4000 and 5200ft.  As precipitation moves from snow, to sleet, to freezing rain, to rain it will add load and stress to the new snow and slabs already on the landscape.  When rain begins you should expect a rapid rise in instability and the likelihood of naturally triggered avalanches.  Rain adds load, melts bonds that were contributing to slab strength, and can percolate down to a buried crust, lens, or blue water ice and lubricate this potential bed surface. 

All of these new issues today are falling on a 1” (2.5cm) crust with recrystalized facets underneath.  This now buried crust varies in strength around the ravines depending on whether or not Monday’s rain event was falling on cold slabs or old surfaces.  This factor determines whether you break right through the crust or stay on top.  The porosity of these old layers had a bearing on facet growth and the current strengths and weaknesses we are dealing.  This leads ultimately to my point that a great deal of spatial variability exists across the mountain.  In some locations today new loading from the south may collapse areas with deep facets under the crust and may not in others.  More probable will be the potential that avalanches in today’s new snow and rain may step down and rip out some locations of this crust.  Although today’s new precipitation is by far the main issue triggering the High danger rating this buried problem is one more factor to consider.

Tonight winds will rage, gusting far in excess of 100mph (160 kph).  This should be able to overwhelm any new encapsulation that occur today to move a variety of crystal types and ice pellets down into avalanche terrain causing new problems for tomorrow.  We’ll have to see exactly how this event plays out today to better assess this subject.   Check back for our Weekend Update later today.

The Lion Head Winter Route is now open. This is a steep route; an ice axe and crampons are highly recommended for safe travel. Please avoid the summer Lion Head Trail due to avalanche risk. The Sherburne Ski Trail should be a reasonable choice this morning but expect it to get heavier and turn into some challenging mash potato-glop later.  Buried obstacles still exist although they are becoming less of an issue.

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 8:10am. 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

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