Avalanche Advisory for Thursday March 6, 2014

Expires at Midnight

Tuckerman Ravine has Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully.  The Little Headwall has Low danger.

Huntington Ravine has Moderate and Low avalanche danger. Yale, Central Gully, and South gullies have Moderate danger. Natural avalanches are unlikely and human triggered avalanches are possible. All other forecast areas have Low avalanche danger. Natural and human triggered avalanches are unlikely, except in isolated terrain features.

AVALANCHE PROBLEMS: New Wind Slabs loaded in the deposition zones from W winds yesterday is the primary avalanche problem today.  This loaded over wind slab instabilities that were created during the past several days.  The most widespread wind slab problems can be found in the Sluice through the Chute of Tuckerman. They are interspersed with the secondary problem, Persistent Slabs.  These are in the form of older pencil hard wind slabs in varying stages of faceting above and below the crust.  This faceting is creating a wide range of variability across our forecast areas.

WEATHER: The summit picked up 2.7” (1.75cm) in the last 48 hours, 2.1” (5.2cm) of which fell on Wednesday.  Clear conditions prevail this morning, dawning cold with a pink alpine hue across the east facing terrain.  Temperatures will rebound from subzero temperatures to the singles F, while winds fall from a current of 23mph (37kph) from the NNE, to 5-20 (8-32kph) from the NW later today. Expect cold air in place overnight before starting a slow warm up into Saturday.

SNOWPACK: Yesterday 2.1” of new snow, with a density of 6.6%, was delivered on modest winds from the W and WNW between 10 and 35mph (16-56 kph).  This has laid a surprisingly consistent new soft slab across Tuckerman making her as picturesque as she’s been all winter. As you would expect, I believe the main issue and avalanche problem is in the steepest strong lee of the Ravine from the Sluice over to the Chute.  In Huntington the upper half of Yale has new soft slabs from cliff wall to cliff wall forcing a climber through instabilities, unless he/her get up on rock faces.  South Gully has new enough slabs to bump it to Moderate, but barley so.  Areas posted at Low do have isolated pockets of instability that could be triggered, but are easily avoided, so pay attention to your travel route.  In both Ravines expect these new slabs to be thin, very soft, and touchy.  The new low density snow above treeline will likely sit in place due to benign winds over the next day.

You are likely getting a little tired of the crust discussion, but unfortunately it makes it no less of an issue.  The weakening crust has early facets growing both under and over it, which has been a driver for our persistent slab problem.   Some of yesterday’s discussion is still valid so….“As you travel this crust should be a reference point to look for in your snowpack evaluations.  Mainly, how deep in the snowpack is this crust?  In places where newer wind slabs are layered over the crust I would focus attention to how the upper slabs closer to the surface are bonded between hardness transitions first. Then, focus on the facet development just above this breakable layer.  This priority will be dependent on depth of the crust and the degree of facet development.”  A failure in the new wind slab from last night could step down near this crust layer.

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 3-06-2014. 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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