All forecast areas of Tuckerman Ravine have MODERATE avalanche danger. Heightened avalanche conditions exist. Evaluate snow and terrain carefully and identify features of concern. Lobster Claw, Lower Snowfields, and the Little Headwall are not posted due to lack of snow cover. Exercise caution in these areas.
Huntington Ravine has Moderate avalanche danger in Central, Pinnacle, Odell, and South gullies. Heightened avalanche conditions exist. Evaluate snow and terrain carefully and identify features of concern. All other forecast areas are not posted due to lack of snow cover.
AVALANCHE PROBLEM: Two problems will develop today, wet loose avalanches and persistent slab avalanches. The amount and type of incoming precipitation today will determine the magnitude of the problem. Naturally-triggered avalanche activity is possible, however, the most likely situation holds the avalanche potential to smaller wet slides. Wet loose avalanches may take place as the freshly fallen snow is subjected to sleet and rain. These will be possible everywhere, but northerly facing slopes may have greater amounts of new snow blown in before any rain falls. With this problem, it will be easy for a person to trigger a slide.
The second problem, persistent slabs, may come into play late today as rain further saturates the existing snowpack. Compared to the wet avalanche problem, today’s persistent slabs have greater uncertainty and unpredictability, as well as a greater potential for the avalanche to be larger. The primary locations where this problem might be seen are in the Lip, Center Bowl, and Chute of Tuckerman and in Central Gully of Huntington.
WEATHER: Expect some snowfall this morning, perhaps a few inches, blowing in on increasing southerly and southwesterly winds. This will transition to sleet and rain as warm air continues to invade. Except for the warm temperatures, there is nothing nice about today’s weather forecast. And if you like snow, the warm temperatures are not your friend, either. Be sure to check the complete weather forecast before heading above treeline. Total liquid equivalents for this system may range from 0.75” to 1.25” (2-3cm).
SNOWPACK: Despite an overall lean snowpack, what is on the ground in Tuckerman is at least interesting from a forecaster’s perspective. In much of the Lip and Center Bowl (where the greatest avalanche potential is held), previous avalanche activity has kept an old rain crust reasonably close to the surface. In the steepest sections such as under the ice, some windslab was able to develop on top of the crust. In other locations the crusts are more deeply buried, but other issues (e.g. faceted snow) may be a more prominent factor in today’s avalanche hazard. Regardless of the location, earlier this week warm temperatures brought the surface snow layer up above freezing, then it fell back into a refreeze late Monday, adding strength and stability to the upper snowpack. It’s largely this added strength that is making me think the persistent slab problem will be able to withstand today’s precipitation. If much of the precipitation today comes as liquid rain at the ravine elevations, there will be a greater destabilizing impact on the existing snowpack. Expect danger ratings to reach or exceed Moderate if this should happen.
· 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 7:50a.m. February 3, 2016. A new advisory will be issued tomorrow.
Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856