Avalanche Advisory for Thursday, December 29, 2016

This advisory expires at Midnight tonight.

Huntington Ravine and Tuckerman Ravine avalanche danger will increase from LOW to CONSIDERABLE today. All forecast areas will have CONSIDERABLE avalanche danger. Natural avalanches will be possible and human-triggered avalanches likely. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential.

Avalanche danger will rapidly increase through the afternoon and evening hours. Travel in avalanche terrain near and after dark is not recommended.

AVALANCHE PROBLEM: Wind Slab and Storm Slab will compete for the primary avalanche hazard position today. Snow will increase in intensity in the afternoon, increasing our avalanche hazard from the current Low rating towards Considerable as natural avalanches become possible and human-triggered avalanches become more likely. By evening and overnight, large or widespread natural avalanches will become likely as snowfall rates increase. Safe travel today will be all about timing and keeping an eye on rates of snowfall, ridgetop winds, and other people above you acting as triggers. A hard, icy bed surface will make self-arrest and escape from even a small avalanche very difficult.

 WEATHER: Though the MWObs summit forecast today is for calm E and NE winds in the 10 mph range, NWS predicts higher wind speeds at 30-40 mph from the SE. Model suites bear out the NWS forecast more closely as do the current summit wind speed and direction from the S at 33 mph. Either of these forecast wind directions and speeds will create cross-loading conditions to some degree in the lee aspects of a predominately easterly wind direction today. Anticipate visibility to deteriorate rapidly as summit fog and snow descend. The temperature will increase into the high teens in the afternoon. This warming will contribute to the unstable situation by increasing the density of new snow. Wind and snowfall rates will intensify this evening and overnight with large or widespread natural avalanches occurring.

SNOWPACK: Our terrain is dominated by a wind scoured knife hard, icy melt-freeze crust with some pockets of pooled rimed crystals and graupel rounds resting on surprisingly steep benches. History has shown that new snow will bond on this type of crust, at least initially. If we receive the forecast 3-6” of snow today on relatively light easterly wind, it is quite likely that we will not see any natural avalanche activity during daylight hours. That said, I would expect quite a bit of spindrift or dry-loose avalanches on ice climbs due to low temperatures and a strong likelihood of dry light snow at the start of the storm. The small dry-loose avalanches will build the slabs we typically see beneath very steep (55 degrees or more) terrain such as the first pitch of Pinnacle and mid-slope Center Bowl. Lots of challenging weather with what is looking like a snowmageddon situation. Threading the needle today to play safely in the mountains may be possible but the margin for error is extremely slim. Expect avalanche danger to continue to increase tonight and through tomorrow as west winds ramp up and load the expected 20-30” of snow into east facing terrain.

The Lion Head Winter Route is open and the most direct route to the summit. The Tuckerman Ravine Trail bridge is completed enough to allow traffic again so you can avoid the detour. Please be careful of construction debris near crossover 7 on the Sherburne Trail and watch out for machine traffic on the Tucks and Sherburne Trail today.

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 8:15 a.m., Thursday, December 29, 2016. A new advisory will be issued tomorrow.

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

2016-12-29