Avalanche Advisory for Sunday, March 4, 2018

Huntington and Tuckerman Ravines have LOW avalanche danger. All forecast areas have Low avalanche danger. Watch for unstable snow on isolated terrain features.

 AVALANCHE PROBLEM: Isolated and avoidable pockets of wind slab are scattered through our terrain, with the more dominant snow surface being old refrozen snow. A trace to 2” of new snow and wind late today could result in further development of wind slab in similarly isolated pockets. These relatively small wind slabs likely will remain sensitive to a human trigger but should be straightforward to avoid. The old, hard, and slick refrozen surface will appear distinctly grey in contrast to the white wind slab. Of equal or greater concern than avalanches today are long sliding falls on this old surface. A loss of footing on steep snow, be it from a stumble or even a small avalanche, is likely to result in a high speed slide on this particularly slick surface. Choose terrain carefully and consider the consequences of such a fall, as rocks and other hazards are in the fall line of many steep slopes. Self-arrest in the current conditions is unlikely to impossible.

WEATHER: Minimal flurries yesterday morning tapered early as skies became at least partly sunny for much of the day. A high temperature of 22F was recorded on the summit and Hermit Lake stayed just below freezing. NE summit winds around 40 mph resulted in little if any snow transportation on the ground. We will likely see at least a few snowflakes fall today, with peak precipitation late this evening resulting in up to 2” of snowfall. NE wind on the summit will increase slightly through the day from 30 mph to near 50 mph tonight. Temperatures should be steady, with low teens F forecast on the summit. Similar conditions with minimal if any snow accumulation are expected tomorrow.

SNOWPACK: The old refrozen surface is proving difficult for new snow to stick to. As a result, it is the primary snow surface in the Ravines. Pockets of wind slab do exist and we expect generally poor bonding to this icy bed surface, but with visibility you can navigate around these pockets and avoid today’s avalanche problem. Additional snow late today should behave similarly and be easily transported by wind to produce isolated new slabs and leave significant old surface exposed. The series of melt/freeze cycles which formed this icy surface also allowed the deeper snowpack to stabilize and limits avalanche concerns to slabs on the surface. Icy snow surfaces are not uncommon in our terrain, but be aware that this one is particularly hard and smooth which allows a sliding person to accelerate quickly and all but eliminates the possibility of self-arrest. Climbers will find good crampon purchase while skiers struggle to find many options to link turns in edge-able snow. The John Sherburne Ski Trail has improved over the past few days with reports of very thin cover in some sections by generally happy skiers and riders.

The Harvard Cabin will be closed Tuesday and Wednesday of this week. 

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 7:35 a.m., Sunday, March 4, 2018. A new advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

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