All forecast areas in Huntington Ravine will have CONSIDERABLE avalanche danger. Natural avalanches are possible and human triggered avalanches will be likely during daylight hours. Avalanche danger will rise to High this evening with natural avalanches becoming likely. Dangerous avalanche conditions will exist this afternoon.
Tuckerman Ravine will have HIGH and CONSIDERABLE avalanche danger. Sluice, Lip, Center Bowl, and Chute will have High avalanche danger. Natural avalanches will become likely and human triggered avalanches will be very likely. All other forecast areas will have Considerable avalanche danger. Natural avalanches will be possible and human triggered avalanches likely. The Little Headwall still has open water and is not a recommended route.
DANGEROUS AVALANCHE CONDITIONS WILL DEVELOP THIS AFTERNOON.
AVALANCHE PROBLEM: Wind slabs developing this afternoon will build rapidly and create dangerous avalanche conditions in and below steep terrain. Due to the steepness of most of our terrain and the speed and intensity of new snowfall, it would be extremely challenging to find stable snow among the developing storm slab anywhere in our forecast areas. By late afternoon, expect wind slabs to trend larger and more sensitive to human triggering as wind ramps up and blows across our smaller northern fetch zones. In the evening, natural avalanches could begin running into the floor or lower angled areas of both ravines.
WEATHER: Heavy snow and wind wrapping through the east this afternoon is driving our avalanche rating. New snow totals largely depend on banding and as a result total amounts during the day are followed by a question mark, though 8-12” seems likely by dark. One thing that is certain is the high wind that will accompany this storm as it passes through tonight. Wind speeds through the late morning as snow begins may remain moderate in the 20-35 mph range from the southeast. But peak snowfall in the afternoon will be accompanied by loading velocity winds which will continue to shift towards the north, through the east, and increase. Wind will reach the 50-60 mph range from the NE by nightfall. Temperatures will remain around 10F with light density and easily wind transported snow.
SNOWPACK: Cross-loading of terrain features and start zones will create cohesive slabs on top of weaker, lower density snow. High rated areas are starting out with some soft new snow from some light wind loading that occurred the day before yesterday. These areas seem likely to produce larger avalanches due to this layer, as well as their location downwind of a larger fetch zone. Expect Lobster Claw and Right Gully, which have been lacking snow near the ridgeline, to quickly fill in on this afternoon’s wind, with natural avalanches trending towards likely. As wind shifts further west overnight, more snow will be available to the wind and wind slabs will grow much larger in both ravines. Expect elevated avalanche danger tomorrow, possibly exceeding today’s danger ratings.
The Lion Head Winter Route is the safer route to the summit on the east side. Both the Tuckerman and Huntington Ravine Trails as well as the Lion Head Summer Route pass through several avalanche paths and are challenging mountaineering routes with significant avalanche hazard.
• Safe travel in avalanche terrain requires training and experience. This bulletin 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 8:03 a.m., Thursday, January 4, 2018. 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