Avalanche Advisory for Tuesday, March 14, 2017

This advisory expires at Midnight.

Huntington and Tuckerman Ravine have CONSIDERABLE avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route-finding, and conservative decision-making are essential.

AVALANCHE PROBLEM: The incoming Nor’easter will create Wind Slab in avalanche terrain. Wind direction will dictate where this problem forms and to what degree loading happens with increasing hazard through the day. Light south winds this morning will load north-facing slopes during the morning. As the wind shifts to the east and increases in speed, north-facing as well as south-facing slopes will see cross-loading. While our forecast areas do not include slopes with a western aspect, west-facing slopes outside of our forecast area will see significant wind loading as the wind shifts to the east. As the wind direction continues its move toward the north, south-facing slopes will see the most loading with cross-loading finally bringing snow to east-facing slopes. As this shift to the N and NW takes place, areas in Tuckerman and Huntington Ravine may exceed the Considerable rating after this advisory expires at midnight. Much of the snow from today will move to the west side of Mount Washington. Looking ahead to later tonight and tomorrow, NW winds will bring this snow back to the east side, likely leading to multiple avalanche cycles.

WEATHER: Paying close attention to the changing weather today will be paramount for safe travel. Snow is now falling at Hermit Lake. Currently on the Summit, winds are 15mph from the S. As the morning progresses, wind speed will increase and shift to the E by early afternoon. Wind speeds will depend on how the storm tracks. At the moment, wind speeds reaching close to 100mph seems likely at some point this evening. With snowfall reaching its heaviest (2-3” per hour) in the afternoon/evening hours, wind direction will continue wrapping counter-clockwise, reaching due N around the time this advisory expires. Snowfall total will be significant with quite possibly 12” by dark and close to this same amount by morning tomorrow.

SNOWPACK: Our base snowpack went through a significant melt-freeze cycle at the end of February and is solid. Since then, we recorded about 16” of snow that has seen strong wind. Much of the terrain was scoured and wind slab that formed in the lee areas of steep terrain and behind terrain features is firm and proven unreactive to human triggers. The weak layer that exists under this wind slab will be tested by avalanche cycles over the next 36 hours. Stepping down into this layer is a possibility overnight and into tomorrow. Incoming snow and the shifting wind today will be the real factor affecting decision-making. Expect limited visibility due to blowing snow, requiring meticulous navigation with a constant eye on the changing wind.


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 8:30 a.m., Tuesday, March 14, 2017. 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