This advisory expires at 12:00 midnight.
Tuckerman and Huntington Ravines have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible in all forecast areas. Evaluate snow and terrain carefully. The only exception to this rating is the Little Headwall in Tuckerman, which has Low avalanche danger. Natural and human triggered avalanches are unlikely there. Unstable snow may exist in isolated terrain features.
AVALANCHE PROBLEM: Avalanche problem #1 today is Wet Slab due to saturated snow over dryer, weaker snow. Two inches of snow fell on moderate winds in the 50’s mph yesterday and built wind slabs which may become more reactive to triggering today due to warming temperatures. Problem #2 is deeper Persistent Slab which also may be activated by increased loading from yesterday coupled with warming temperatures.
WEATHER: Diminishing winds and clearing skies are forecast this morning and may lead to heating of the snowpack. The timing of the clearing and warming have will have a direct effect on stability today. If fog lingers and shades the slopes from the sun, our stability concerns will be reduced. The temperature is forecast to reach 30F on the summit with winds dropping to 10-25 mph (SE) from an already low 25-40 mph (NW). As the fog burns off, anticipate the possibility of rapid warming.
SNOWPACK: Icy conditions exist on the trail due to yesterday’s changeover from snow to rain which froze over the surface. Not only will this make travel more exciting due to the potential for rapid acceleration if you fall, but this ice is a player in our stability today. The wet surface layer, which exists over colder dry snow, is cohesive and relatively strong as long as it stays frozen. When heated, this thin layer of ice crust will lose its strength and create the potential for a Wet Slab or even a deeper weak layer, to release. Warming today is the enemy of stability and areas with the greatest consequences from this effect are those areas with large expanses of slab. These wind slabs developed yesterday in the lee of westerly winds from 1.8” of snow (0.57”SWE). Central, Sluice, Center Bowl and Chute are standouts for large wind slabs. The steepest terrain in Huntington ice climbs would also be vulnerable today as the slab battles gravity. South facing slopes will react soonest to solar gain. I would not expect the typical signs of rapid solar warming to occur today; the pinwheels and wet sluffs you often see in fresh snow will probably be contained by the glaze of ice. The monster lurking in the basement for me is the presence of some weak interfaces between older windslabs as well as some areas of pooled, rimed snow which have been very stubborn, but would have devastating consequences if triggered. Because of this “Scary Moderate” comes to mind. The unobvious nature of these deeper slabs are why we carry beacons, probes and shovels and practice careful travel techniques (minimizing time spent in the fall line of avalanche paths, one at a time travel, etc.). It may feel more like spring today but the snowpack stills tells me that it is winter.
- 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. 3-29-2014. 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