This advisory expires tonight at 12:00 midnight.
All forecast areas of Tuckerman Ravine and Huntington Ravine have CONSIDERABLE avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Careful snowpack and weather evaluation, cautious route finding and conservative decision-making are essential. Lobster Claw, Lower Snowfields and the Little Headwall are not posted due to lack of snow coverage.
AVALANCHE PROBLEM: Wind slab avalanches are threat #1 today. 1-3” of new snow plus 8” in the past 24 hours with increasing winds today will build wind slabs which are likely to be reactive to human triggers or become thick and heavy enough to avalanche naturally. Persistent slabs, which were weakened by yesterday’s warming trend, are a distant second to the primary threat but could easily contribute to the mass of snow available to an avalanche in the wind slab.
WEATHER: WNW then NW winds are expected to increase into the 100 mph (160 kph) range later today and into the night. Before we reach that high velocity, which often scours out much of Huntington and many areas in Tuckerman, we will pass through velocities ideal for loading lighter, new snow into the ravines. Visibility will be limited by summit fog and blowing and drifting snow. Temperatures will reach down to around 10F (-12C).
SNOWPACK: Recreationalists and our snowpack dodged a bullet yesterday when precipitation fell as snow instead of rain above the 3800’ level. Due to the heavy nature of the 8” (20cm) which fell yesterday and yesterday evening, the wind loading period today may be prolonged. The 4” of snow yesterday afternoon was around 25% density and fell on top of the earlier 4” of 20% density snow. The new snow falling through the day today will be much lighter than the snow being wind loaded into the terrain later. This structure will be a classic “upside down” structure as the denser snow is loaded on top of an already inverted snowpack.
Yesterday’s snow was dense enough at Hermit Lake to form a firm crust but lower temperatures on the summit and Alpine Garden yesterday allowed this snow to remain drier and therefore more prone to be moved by the wind today. It will be worth considering the weak layer of facets widely distributed through the terrain as well as areas of older wind slab in Sluice through Chute that could be activated by an increased load of new wind slab. It will be a heads up day for making field assessments or traveling around in either ravine.
The Sherburne had picked up a couple inches of new snow overnight but some of the water bars and stream crossing are just beginning to refreeze.
- 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 9:00 a.m. January 19, 2015. A new advisory will be issued tomorrow.
Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856