Avalanche Advisory for Monday, April 9, 2018

Huntington Ravine has MODERATE and LOW avalanche danger. Yale, Central, Pinnacle, Odell, South, and Escape Hatch gullies have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern. North and Damnation gullies have Low avalanche danger. Watch for unstable snow on isolated terrain features.

Tuckerman Ravine has MODERATE avalanche danger. All forecast areas have Moderate avalanche danger. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. The Little Headwall is the exception to this rating with Low avalanche danger and areas of open water.

 AVALANCHE PROBLEM: Wind slab formed Friday night is our primary avalanche problem, with a secondary problem of smaller wind slab formed from the few inches of new snow that fell on strong W wind last night. The older wind slab has been observed up to 14” thick. It varies in thickness and bonding to the old refrozen crust beneath it, but has gained some strength since Saturday’s widespread human-triggered avalanche cycle. Visibility is limited this morning, but we expect that the new wind slab exists in relatively small pockets throughout the terrain. Today is a “small avalanches in many areas” kind of Moderate rating. We don’t expect any terrain to produce particularly large avalanches, with the old wind slab showing variable stability and the new wind slab suspected to be small. Relatively small avalanches can still bury, injure, or kill a person, especially if they happen in high consequence terrain with rocks, cliffs, vegetation, or other hazards in the runout. If avalanches aren’t enough to make you choose lower consequence terrain, be aware that the refrozen crust which exists at the surface in areas is very hard and could easily allow a long sliding fall.

WEATHER: Three inches of snow was recorded last night at Hermit Lake, with just one inch recorded on the summit. This snow fell on 50-70 mph W wind that continues currently. Snowfall has subsided, beginning a trend towards clearing skies today as wind may briefly shift NW before diminishing to below 40 mph on the summit by midday. Temperatures will be cold, with a summit high in the single digits above zero F. Tonight and tomorrow are forecast to have mostly cloudy skies, slightly warmer temperatures, and W summit wind in the 10-30 mph range. We may receive a few inches from upslope snow showers late Tuesday as winter conditions in April continue.

SNOWPACK: The wind slab formed Friday night proved to be reactive over the weekend, with at least eight human triggered avalanches that were all relatively small. Though these slabs have gained some stability over the past two days, new slabs formed overnight should be touchy though small in size. The bed surface of concern is our old refrozen and thick crust from melt/freeze cycles over the past two weeks. We don’t expect deeper instabilities to be a concern currently. Spatial variability is high today, with inconsistent bonding of the older wind slab and pockets of new, touchy wind slab. Areas of exposed refrozen crust where you won’t trigger an avalanche will be visible once clearing occurs later today, but the new and old wind slabs will appear very similar visually. This spatial variability means that it will also be difficult to apply stability tests results across terrain, as is often the case with wind slab. Backcountry travelers exercising careful terrain selection should be able to find favorable conditions among our varied surface snow, and skiers and riders should still enjoy the John Sherburne Ski Trail.

 Boston folks: Join us on Tomorrow, April 10, from 7-10 pm at Arc’teryx Boston for a night of learning, socializing, and free gear! Free to attend, but space in limited, register at eventbrite.com.

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  8:00 a.m., Monday, April 9, 2018. A new advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2858

2018-04-09