Avalanche Advisory for Friday, April 4, 2014

This advisory expires at Midnight.

Tuckerman and Huntington Ravines have LOW avalanche danger.  Natural and human triggered avalanches are unlikely except on isolated terrain features.

Slopes with south facing aspects have the potential to lose strength starting in the early afternoon hours. The potential for a human triggered avalanche will increase when this happens. Low danger doesn’t mean no danger.

AVALANCHE PROBLEMS: Persistent slab remains the main threat today on south facing aspects. While we are starting out the day with very low avalanche probability due to a strong, refrozen snowpack, the intense April sun could heat surface slabs. Wet slabs could also become a concern today if and when this heating occurs. Sluice and Lip are the slopes with the highest probability and consequences for these problems, with portions of North, Damnation and Yale close behind.

WEATHER:  Light winds on the summit this morning (20 mph) will increase a bit in the afternoon as overcast skies filter in as the next precipitation maker approaches. A temperature inversion exists this morning with Pinkham standing at 19F while the 4300′ temperature is 27F. By sundown, mixed precipitation should begin with the form determined by your elevation. 2-4″ of sleet and snow are forecast for tonight.

SNOWPACK:  Light wind and sun today will compete with cool temperatures in the struggle to soften the snow surface on south facing aspects. Temperatures in the teens to mid-20’s for the past 24 hours kept the snow surface frozen; however, a “greenhouse” effect from high thin clouds coupled with light wind could lead to heating of the snow in the early afternoon hours. Many folks intent on skiing were skunked yesterday by the cold refrozen snow following Monday and Tuesday’s warm-up. I believe the difference today will be overnight temperatures, which were 10 F warmer last night than the previous night, lower windspeeds and the greenhouse effect of high clouds. An approaching warm front will allow filtered  solar radiation to reflect back into the lower atmosphere and nudge temperatures higher. Of course, it will be a very close call today, so I would certainly plan a strategy to turn around early and carry tools to prevent a long sliding fall on icy terrain that hasn’t softened. Solar gain in the snow is the main driver of our avalanche hazard today as deeper weak layers are bridged over by a stiff slab of refrozen snow. The frozen surface is helping to keep the spread out the stress of humans  through the upper layers. Generally, this bridging will continue even if the limited heating pans out today. One other factor in our favor is the the weakest of our weak layers has been swept out of most of the Lip and some of the Sluice by avalanches after the ice crust and faceting occured. That said, I would still practice safe travel techniques and carry avy gear. Right Gully and Lobster Claw are mostly free of this layer and benefit from other stability factors.

OTHER HAZARDS:  Long sliding falls are a hazard today. Icy, refrozen snow will limit penetration of boots or skis. Crampons and an ice axe are recommended for travel on steeper slopes. Micro-spikes and other creeper style traction devices maybe helpful on some low angle approach summer trails, but they do not provide the security of crampons.  Also begin looking for undermined snow bridges and open holes, most likely found moving down the brook bed from the Bowl to the Little Headwall. The Harvard Cabin is closed for the season.

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. Posted 8:15a.m. 4-4-2014. 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

2014-04-04