Avalanche Advisory for Saturday, March 25, 2017

This advisory expires at Midnight.

Friends of Mount Washington Avalanche Center is hosting the White Mountain Challenge event today to support our mission. Check out this link for more information on this 9 Ski Mountains in 9 Hours event or to donate.

Huntington Ravine will have CONSIDERABLE and MODERATE avalanche danger. Central, Pinnacle and Odell Gully have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches possible.

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. Sluice, Lip, Center Bowl and Chute will have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. All other forecast areas except the Little Headwall have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches possible. Little Headwall has Low avalanche danger. Natural and human-triggered avalanches are unlikely.

AVALANCHE PROBLEM: Wind slabs formed from 7” of new snow on west winds in the past 24 hours keeps the likelihood of human-triggered avalanches in the considerable range. Wind velocities were ideal for loading slopes with an east facing aspect. These slabs are likely to be soft enough to be sensitive to a human-trigger and may be large enough to carry you downhill and possibly bury. Though the threat of natural avalanches is by and large past, the likelihood of human-triggered avalanches makes careful evaluation of snowpack, cautious route-finding and conservative decision making essential. Dense summit fog is currently hampering our ability to make observations so consider each avalanche path to be loaded and waiting for a trigger until you confirm otherwise. Forecast areas with a moderate rating are solidly in that range so assess snow and terrain carefully. A disparity in recorded snowfall between the summit and our forecast elevations gives us some uncertainty about the size of potential avalanches today but this shouldn’t change you travel precautions in avalanche terrain.

WEATHER: Snowfall late yesterday and into the night reached the upper end of forecasted totals, with 6.7 inches recorded at the summit, 2.4” at Hermit Lake and 2.75” at Harvard Cabin in the past 24 hours. Density at Hermit Lake was 17% with a fair amount of rimed particles. This snow fell on West wind blowing near 50 mph and summit temperature has held steady in the high teens to 20F. Wind shifted NW early this morning, is currently decreasing, and is forecast to continue out of the NW with velocities of around 25 mph through tonight. Cloud cover should decrease throughout the day with at least partial clearing likely by late afternoon. If this clearing occurs sooner than expected, solar energy could warm the newly formed wind slabs and increase instability on sunny aspects.

SNOWPACK: Winter continues on Mt. Washington, with new snow transported by west and northwest wind creating today’s layer of concern.  A lack of visibility into the ravines this morning limits capacity for observation.  The recorded wind speeds in the past 24 hours will have built wind slab in areas lee to a west wind, particularly in the upper start zones.  This layer will be relatively soft and sensitive to a human trigger.  The surface beneath this new snow varies.  Firm wind deposited snow and textured sastrugi snow exist over much of the terrain, a layer unlikely but not impossible to fracture and contribute to total mass of snow if an avalanche were to occur in the surface slab.  The Sluice and Lip hold the highest probability of such an avalanche.  Two exceptions to this wind deposited pre-storm surface can be found: A melt-freeze crust in pockets of southerly aspects and an older rain crust in areas scoured by wind earlier this week, particularly Left Gully.

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 Harvard Cabin.

Posted 7:45 a.m., Saturday, March 25, 2017. A new advisory will be issued tomorrow.

Frank Carus/Ryan Matz, Snow Rangers
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2017-03-25