Avalanche Advisory for Monday, April 3, 2017

This avalanche advisory expires at Midnight.

Huntington Ravine will have CONSIDERABLE and MODERATE avalanche danger. North, Damnation, and Yale will have Considerable avalanche danger. Natural avalanches will become possible with human-triggered avalanches likely. All other forecast areas will have Moderate avalanche danger. Natural avalanches will be unlikely and human-triggered avalanches will become possible.

Tuckerman Ravine will also have CONSIDERABLE and MODERATE avalanche danger. Sluice, Lip, Center Bowl and Chute will have Considerable avalanche danger. Natural avalanches will become possible with human-triggered avalanches likely. Lobster Claw, Right Gully, Left Gully, Hillman’s Highway and Lower Snowfields will have Moderate avalanche danger.  Natural avalanches will be unlikely and human-triggered avalanches will become possible. Little Headwall is not rated due to skier compaction, exposed ice, rocks and open water.

AVALANCHE PROBLEM: Wet slab and wet loose avalanches will create unstable conditions as heating resumes today. The upper snowpack (10-20cm) of south facing aspects were heated by the sun yesterday and refroze overnight, creating low avalanche danger this morning. Cold, dry snow remains below that melt/freeze crust which will heat up rapidly today due warm air temperatures and clear skies. Slopes with an east and south facing aspect will heat to the point that a wet loose sluff, or skier or climber, could trigger a larger wet slab avalanche. Areas of wind slab that developed Saturday night, and to a lesser extent last night, will become unstable due to this heating. Unlike the human-triggered, soft wind slabs over the weekend, today’s avalanches could break further upslope above you, making them more likely to capture and carry you. Old or new tracks on a slope today do not mean that the slope won’t avalanche.

WEATHER: The high temperature on the Summit yesterday reached 21F. Summit fog lingered for most of the day, but both Ravines saw clearing for extended periods. Overnight, winds gusted to 60 mph from the NW with a current speed of 53 mph. This wind should continue to diminish today, possibly decreasing into the teens by dark. High pressure over the region will allow for clear skies for most of the day with clouds possibly moving in ahead of the approaching low tonight. Temperature today will reach into the upper 20’s F on the summit. The approaching low may bring up to 2” of snow tonight.

 SNOWPACK: Little old surface is exposed after the 12”+ of snow fell Friday and Saturday. Old surface that exists tends to be at the very top of forecast areas. The new snow has proven to be reactive, with four human-triggered avalanches over the weekend in our forecast area alone. As radiation and solar gain heated the snowpack yesterday, aspects that received the most sun saw the top 20cm of snow become saturated. This wet snow continued to be reactive in tests in the afternoon with the interface of wet and dry snow acting as the sliding surface. A snowfield on Lion Head propagated a small wet slab from snow falling off a tree and a similar event caused a medium-sized wet loose slide to run in the Lip. These two events are examples of what may take place today, though with clearer skies, warmer temperatures, and lower wind speeds, the wet layer will be much thicker making these events potentially more widespread and likely larger.

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 7:50 a.m., Monday, April 3, 2017. A new advisory will be issued tomorrow.

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

2017-04-03