Avalanche Advisory for Sunday, December 18, 2016

All forecast areas of Huntington and Tuckerman Ravine have CONSIDERABLE avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Dangerous avalanche conditions will exist today. Cautious route-finding and conservative decision making are essential. Little Headwall and Lower Snowfield are not forecast due to lack of snow.

AVALANCHE PROBLEM: Wet Slabs are the primary avalanche problem today. These are notoriously hard to predict and can range from small pockets to large and destructive avalanches. Wet slabs could occur in any of our avalanche paths and may release deep in the snowpack. There many variables that influence the release of these wet slabs. Whether the rain overwhelms the tensile and shear strength of our existing slabs, or percolates through to lubricate the melt-freeze crust or adjusts to the increased load without avalanching are all too complex to forecast with much certainty. Given the avalanche danger and the unsupportive walking or climbing surface, you might ask yourself why would you bother to enter avalanche terrain. With precipitation forecasted throughout the day, we may see a new layer of wind slab form on the refrozen snow pack. Also be aware of the potential for undermined snow, particularly if crossing streams or rivers.

WEATHER: If you dont like the weather, just wait five minutes. Arctic cold, snow, rain, 50 degrees, more snow, wind chill warnings. Enough said. Saturday began at -6F with 35mph W winds. Snow began to fall around 6am and continued until 3pm, delivering 6.5”, with the heaviest snowfall occurring around noon. This snow arrived on 30-55mph S and SW winds. By midnight, temps rose to 32F with steady 65mph W/WSW winds. Overnight and into this morning, the summit recorded steady rain and a further increase of temperatures. At 7am, the summit and Pinkham were at 39F with Hermit Lake at 49F. It looks like rain will continue this morning, transitioning to sleet, ice, and then back to snow as temperatures begin their plummet. By late-morning, we should see the summit drop below freezing with a steady decline to sub-zero by Monday.

SNOWPACK: Friday was the first day in over a week we recorded no new snow. Field time revealed crown lines and debris in both ravines. The 6.5” of snow that fell yesterday was subjected to good loading speeds throughout the afternoon. These west winds loaded the start zones of many of our forecast areas. Over the course of the night, these newly formed wind slabs were topped with .31” of rain. This is our first rain on snow event of the season, creating the potential for wet slabs which are next to impossible to predict their size and location. Our terrain has rapidly become connected over the past week creating the possibility of the something large coming off the Tuckerman headwall. Wind slabs that formed last night may have already avalanched in certain areas. I would be particularly suspect of slopes that did not avalanche yesterday as the rain soaks and further loads up an already unstable slab. With all this in mind, temperatures will drop today, refreezing this saturated snowpack. As this happens and things begin to lock up, we will see a stabilizing trend turning the surface of our snowpack into a rock hard surface. Travelers in the afternoon and evening should be prepared to use crampons and ice axes to prevent long sliding falls.

The Lion Head Winter Route is now open and the recommended route to the summit from Pinkham. While the construction on bridge on the Tuckerman Ravine Trail continues, the trail is open and the fastest route to Hermit Lake. Those on the Sherburne should be prepared to encounter construction equipment accessing the work site.

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 8:00 a.m., Sunday, December 18, 2016. A new advisory will be issued tomorrow.

Helon Hoffer / Frank Carus, Snow Rangers
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2716

2016-12-18