Avalanche Advisory for Tuesday, February 23, 2016

This advisory expires tonight at 12:00 midnight.

All forecast areas of Tuckerman Ravine have MODERATE avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Heightened avalanche conditions exist. Evaluate snow and terrain carefully and identify features of concern. Lobster Claw, Lower Snowfields, and the Little Headwall are not posted due to lack of snow cover. Exercise caution in these areas.

Huntington Ravine has MODERATE and LOW avalanche danger. Yale, Central, Pinnacle, Odell, South, and Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Evaluate snow and terrain carefully and identify features of concern in these areas. North and Damnation have Low avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features and well-sheltered lee areas.

 AVALANCHE PROBLEM: Wind slab is the primary avalanche problem today. These slabs are varying in size, thickness and location.  Many areas with a Moderate rating can be navigated with wise travel assessments.  Areas rated Low will contain pockets of isolated wind slabs that could be reactive to a human trigger.  All areas will contain some areas of exposed melt-freeze crust.  Wise travel choices will be crucial today.  Runouts to all gullies are slow to fill in and a fall on impenetrable melt-freeze crust or due to being swept by a small isolated pocket of wind slab could have disastrous results.

WEATHER:  The 9″ of snow that arrived over the past weekend arrived on SW and W winds that deposited much of this snow into our ravines.  Temperatures have remained cold, preventing the stabilization of this wind slab.  Yesterday’s sun, while bright and direct, had no warming effect on the snowpack.  Today’s temperatures will be warmer than the past several, however I expect the developing clouds due to the incoming low pressure to prevent further warming. Precipitation will start well after dark and with the significant increase in temperatures expected(in the 40s), tomorrow we’ll be saying, “You should have been here yesterday!”

SNOWPACK: Today, the bottom of my snow pit would be the melt-freeze crust that formed on February 17.  I found it 20cm thick in several places, hard enough that I had to backtrack to put my crampons on, and impossible to put a shovel through.  The wind slab sitting on top of this is incredibly variable, which will make wise travel decisions crucial today.  The wind slab formed on SW winds and since has been subjected to strong W winds for several days.  Lee areas like the climber’s left of Right Gully and approaching the Chute, the top of Hillman’s, Central in Huntington, and the area below the ice in Pinnacle all have smooth surfaces of new snow, clearly indicating this wind slab.  Tests in Right and Left Gully found this slab to fail on CT11-16 on the melt-freeze crust with a shear of Q3.  We also found several layers in the wind slab itself to fail in the CT5-10 range with clean shears.  Our extended column did not propagate.

Throughout both ravines, there is large amounts of debris from the wet avalanche cycle last week.  This can be seen in the runouts of Yale, Central and Pinnacle in Huntington as well as the Center Bowl and Chute in Tuckerman.  Upon approaching the choke of the Chute, we found an 8″ thick flank of a wind slab that avalanched most likely Saturday night.  This was indiscernible from below as it had reloaded with graupel and other heavily rimed particles that fell early Sunday morning.  Evidence of this avalanche cycle was also visible in Right Gully, with a crown 10″ thick tapering to old surface in 10 feet.  The remaining pocket is less than 50 square feet.  I would expect these touchy pockets to linger in multiple areas around the ravines.  Areas of heightened concern today in Huntington would be the start zones of Damnation and Yale, Central Gully, and the snowfields below the ice bulges of Pinnacle and South.  In Tuckerman, I would exercise extra caution in Right, Sluice, the Lip and the Chute.  Other areas harbor smaller pockets of wind slab and larger areas of knife-hard melt-freeze crust that will require crampons even on low-angled slopes.  Spatial variability is the name of the game today.

The Lion Head Winter Route is open and the recommended east-side route to the summit that avoids avalanche terrain. For one of the few times this winter, the John Sherburne Ski Trail looks like good skiing.

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 9:00am, February 23, 2016. A new advisory will be issued tomorrow.

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

02-23-2016