Avalanche Advisory for Thursday December 26th, 2013

This advisory expires today at midnight.

Tuckerman and Huntington Ravines will have MODERATE avalanche danger today. Natural avalanches are unlikely and human triggered avalanches are possible.   This pertains to all forecast areas except Tuckerman’s Lobster Claw, Right Gully, Lower Snowfields and Little Headwall as well as Huntington’s North, Damnation and Yale which all have Low avalanche danger.  Natural and and human triggered avalanches are unlikely except in isolated terrain features.  Depending on accumulations expect an increasing avalanche danger with all areas hedging to the next rating level if forecasted snow fall depths occur earlier than expected.

AVALANCHE PROBLEM:  The existing snowpack at sunrise today is quite stable so we will start the day with very little avalanche concern, but as the day wears on this will change.  Later today Storm Slabs will be something to look out for due to new snow today and tonight.  A Storm slab problem is the concern for a relatively soft cohesive layer of new snow that fractures and fails within the storm snow or on the old snow surface.  This old snow interface is currently slick and hard from the recent ice storm and should make a good sliding surface and conducive to easy shear failure.  We would expect new cold snow to bond poorly to this current surface.  Also expect a Loose Dry Snow avalanche problem in our steepest terrain.  This sluffing of unconsolidated snow is conducive with cold dry snow and slick steep surfaces.  Expect this on climbing routes and other steep or stepped terrain.  Sluffs could build into new cohesive slabs of concern if re-distributed within avalanche terrain causing a secondary problem.  This is a common problem in the Huntington Gullies, particularly Pinnacle, Odell and Central.

WEATHER: Today 2-4” of snow is anticipated with an additional 1-3” tonight.  Winds are currently from the SW at 225 degrees on the compass rose, but are forecasted to shift to the W and gust into the 70’s late in the day.  Winds should subside during the overnight before ramping back up over 80mph tomorrow giving us another loading event from additional snow.  New snow density should be light and fluffy due to temperatures in the 5-10F range.

SNOWPACK: Our snowpack took it on the chin during the severe rain beating ending a few days ago.  Due to this snowpack reboot, this morning you will find a fairly uniform and well bonded snowpack.  I would anticipate the new snow today to bond poorly to the existing surface.  Low density snow crystals will survive a bit better this morning with lower wind speeds than they should this afternoon. Therefore, the initial layer should be a bit softer than slabs developing late in the day.  As winds shift and increase I expect crystal fragments to pack into denser slabs later.  If this scenario plays out a dense cohesive slab may form over a weaker one sitting on an old slick bed surface.  With this said 2-4” today and 1-3” tonight is hardly a major storm, but with building winds from the W and poor to fair bonding expected, new slabs should be respected. Depending on actual totals you shouldn’t be surprised to see increasing instability and increasing avalanche danger.  Also expect tremendous spatial variability as much our terrain is broken up by terrain features and brush.  This will create many isolated problems, often resulting in small avalanches. At a minimum these small avalanches have enough force to knock you down and carry you through the terrain. This is generally true for the majority of both Ravines although larger bed surfaces do exist in The Chute, Left Gully, and Huntington’s Central gully.

In addition to avalanche problems the following hazards should be strongly kept in mind.

Generally icy trail conditions and breakable crust if you venture off the beaten path. We highly recommend crampons and an ice axe for travel in steep terrain or other traction footwear for travel on low elevation hiking trails.  A thin layer of new snow will hide slick sections increasing this icy hazard.  Expect the Sherburne ski trail to be particularly awful if new snow hides water ice, death cookies and frozen turkeys.  I would avoid it as every lump of frozen snow might as well be granite.

Long sliding falls. In those locations where continuous snow coverage exists, the icy surface will make it difficult for you to stop yourself if you were to fall. A thin layer of new low density snow may decrease your friction co-efficient allowing you to break the sound barrier a bit quicker than normal.  Self-arrest must be instantaneous or expect Mach 1 (1126ft/s or 340m/s)  to Mach 1.3 (1464ft/s or 442m/2) speeds followed by the boom of the sound barrier.  Every movement should be done with a deliberate caution.

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 730a.m. 12-26-2013. 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

2013-12-26 Print