This advisory expires at midnight Wednesday 4-10-2013
Tuckerman and Huntington Ravines have MODERATE avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The only exception to this is the Little Headwall which has LOW avalanche danger. Natural and human triggered avalanches are unlikely.
A long expected spring rain scenario finally moved into the mountains yesterday. All told 0.5” (1.2cm) of melted water fell on the summit, the vast majority being rain. Hermit Lake got about the same with .55” (1.4cm) of rain. The Ravines spent a brief period below freezing overnight, but are crawling into melting territory again with some additional rain and fog this morning. This continued melting and new precipitation is the dominate factor in the Moderate ratings today. From this latest event over the past 24 hours, peak snow instability was likely sometime yesterday afternoon. This was due mostly by rain and melted free water making its way down into the snowpack, testing the strength of different layers. As Jeff discussed yesterday, rain weakens snow strength by melting bonds, percolates and lubricates impermeable lens, and adds weight. Due to fog I do not know if we had an avalanche cycle or if slopes stayed put.
The likelihood of avalanche activity has subsided since Tuesday afternoon, but a wet snowpack is still getting our attention. My concerns are substantially less than yesterday as we have passed the rapid stress of Monday’s solar gain followed by initial onset of rain on the mountain’s winter snowpack. However the wet settling snowpack still deserves a “Moderate” rating as it slowly comes down from Tuesday’s “Considerable”. This afternoon some clearing is expected when the summit should reach a peak temperature before falling late in the day into the evening. As this occurs wet surfaces will freeze strengthening the snowpack. The frozen eggshell layer will get thicker and thicker increasing its consolidation through the evening as temperatures fall to 10 degrees F. I would expect all forecast areas to drop to a Low avalanche danger after dark as this occurs.
Some other things to consider today are: 1.Limited visibility this morning will keep you from seeing hazards. 2.Falling ice, albeit limited, could occur today mostly from the Center Bowl and the Sluice up to the climber’s right of the center in Tuckerman. I would consider this to be a concern in all the Huntington gullies. 3.New holes and the initial slots for developing crevasses. 4.Undermining of weak snow near cliff faces and streams could collapse. Give them a wide berth. 5. Difficult off trail travel requiring floatation such as snowshoes or skis.
The Harvard Cabin is closed for the season. The only camping permitting on the eastern side of Mount Washington is at Hermit Lake Shelters.
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 at Hermit Lake Shelters. Posted 8:45a.m. 4-10-2013. A new advisory will be issued tomorrow.
Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856