This advisory expires tonight at 12:00 midnight.
Tuckerman Ravine has Considerable and Moderate avalanche danger today. The Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Dangerous avalanche conditions require cautious route-finding and conservative decision making. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features.
All forecast areas of Huntington Ravine have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features
AVALANCHE PROBLEM: Wind slab is the primary concern today. The driving force behind the increase in ratings today is the new wind slab that developed overnight, and is likely to continue to build today. New hard slabs should be expected in all forecast areas. We anticipate the potential for reasonably large avalanches, with the areas rated Considerable holding the greatest potential for slab failure to step down into deeper layers and produce a larger avalanche.
WEATHER: This was not the storm of the year, but we are happy to have received another 3.5” (9cm) of snow yesterday on top of the 4″ that fell Sunday through Monday. The new snow came along with strong winds shifting from the SW to the NW with peak gusts from the W over 100mph around midnight. This is also around the time when snowfall shut down, but wind loading should be expected today with winds continuing from the W at 60-80mph possibly gusting over the century mark again later. There is a chance we will receive another trace to 2” (5cm) of new snow today, so pay attention to both windblown snow and newly falling snow.
SNOWPACK: The difference in ratings between Considerable areas and Moderate areas is due mostly to the composition of the snowpack prior to the onset of snow yesterday afternoon. Those areas rated at Considerable will have more potential weak layers and weak interfaces between layers. These areas also have steep slopes in the direct lee of W winds that are more protected from the intense scouring of high winds. Prior to new snow, most of those rated Moderate had a stable snowpack due to heavy wind effects and scouring. There is a chance that some of these areas also were scoured last night during strong winds, but until you have the good evidence of this, your best bet is to assume that the slopes were loaded rather than scoured.
If you are out in the ravines today, you will likely have very poor visibility. You’ll need to pay close attention to the amount of snow falling and blowing around. As long as this is going on, you should be thinking about the potential for avalanches to be triggered naturally and running down into relatively flat terrain. It will be very difficult to ascertain if you are in avalanche path runouts without good visuals unless you are extremely familiar with the terrain. As the definition for Considerable danger states, careful snowpack evaluation, cautious route finding, and conservative decision making are essential today.
- 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 8:20a.m. March 4, 2015. A new advisory will be issued tomorrow.
Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2713