This advisory expires at midnight.
Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger. Central, Pinnacle, Odell, and South have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. North, Damnation, Yale, and Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible.
Tuckerman Ravine has CONSIDERABLE, MODERATE, and LOW avalanche danger. Sluice, Lip, Center Bowl, and Chute, have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Lobster Claw, Right Gully, Left Gully, Hillman’s Highway, and Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Little Headwall has Low avalanche danger. Natural and human-triggered avalanches are unlikely.
AVALANCHE PROBLEM: Soft Wind Slabs sensitive to human-triggering developed over the past 36 hours and will continue to grow in size today. While winds may be light, snow that arrived yesterday is light enough in density that wind transport will continue. Signs of blowing snow are visible now as well as the formation of small cornices on top of areas like the Boott Spur gullies. Sluff piles are showing under the steepest terrain in both ravines as well as dry-loose debris below Chute, Left Gully and Hillman’s Highway. The red flags are up today, make sure to take note. Developing wind slab will be soft and sensitive, but is growing thick enough in places that it is struggling to stay in place. Heed these cues when moving into terrain and realize that some snowpack evaluation can be done from below. Cautious route-finding and conservative decision-making will be key today.
WEATHER: Steady snow showers persisted yesterday and continued through the night. Hermit Lake recorded 8cm (3.2”) of 5% snow. This fell on west winds that stayed between 30-45mph. This fell on top of the 11+” that arrived on strong west winds (averaging 70mph) between Thursday and Saturday. High pressure today will allow for clearing but also keep temperatures around 0F. Winds will drop slightly to 20-35mph, shifting from the west to NW early afternoon. Clouds may develop late with cold temperatures tonight and winds increasing up to 50mph.
SNOWPACK: Looking at the snowpack, the base layer currently is the melt-freeze crust that formed last Wednesday. During time in the field yesterday morning, we found widespread soft wind slab that starts at pencil or one finger (P-1F) hardness on top of the crust and transitions to fist (F) hardness at the surface. This was true in several locations between Lobster Claw and Sluice as well as around the lower portions of Chute, the difference being the overall thickness of the slab, with the slab on the right side of the Tuckerman being 30-40cm thick while the left side was much thicker at 85cm+. Compression tests resulted in shearing of interfaces within the slab, but not on the interface of the wind slab and the melt-freeze crust. Extended Column Tests did not propagate. Much of the snow as well as the maximum wind speed yesterday came after our time in the field. The new snow is of light enough density that even the 20-35mph winds today will be enough to provide transport. More soft wind slab will form on top of the layer that already exists. This may begin to form a cohesive slab that could propagate and fracture when stressed by a human-trigger. Snowfields are growing large in size, particularly in the southern gullies in both Ravines, and are connecting forecast areas. Soft slab avalanches today could contain a large amount of snow.
The Lion Head Winter Route is open and the most direct route to the summit from the east. Please be careful of bridge construction debris near crossover 7 on the Sherburne Trail when skiing or riding.
- 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 the Harvard Cabin.
- Posted 8:30 a.m., Monday, January 30, 2017. A new advisory will be issued tomorrow.
Helon Hoffer, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2713