This advisory expires tonight at 12:00 midnight.
All forecast areas of Tuckerman and Huntington Ravines have Considerable avalanche danger. Dangerous avalanche conditions exist. Natural avalanches are possible and human triggered avalanches are likely. Cautious route finding and conservative decision making are essential. The only exception to this is the Little Headwall in Tuckerman, which has Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible in this location.
AVALANCHE PROBLEM: New and developing wind slabs are the primary avalanche problem today. This hazard is already present but will be increasing through the morning. With the current and forecasted wind speeds and direction, all forecast areas will be on the receiving end of wind transported snow, creating dangerous wind slabs that may avalanche multiple times during this cycle. Hiking beyond the first aid cache at the entrance to Tuckerman will put you at risk of avalanches hitting you from up above.
WEATHER: Current visibility at Hermit Lake is limited to about 50 meters. This is from snow, blowing snow, and fog. Expect this to be the dominant weather pattern through the day. Since yesterday morning, we have received about 3” of 10-12% density snow. This snow event started with rimed particles and graupel, then became mostly non-rimed crystal types but with rimed dendrites and graupel still in the mix.
Today’s weather forecast includes up to another 2” of new snow. Most of this is expected to fall this morning. Although winds are expected to diminish this afternoon, you should be prepared for snow to continue loading into the ravines all day.
SNOWPACK: The most important snowpack information you will need to know about today is the rate of wind loading into the avalanche starting zones. Since you won’t easily get to these upper elevation locations where the slabs are developing, and you can’t see it visually, you’ll need to use other available information and your imagination to form a picture of what’s going on up high. This morning, slabs are likely developing quickly and potentially deeply.
In order to recognize the hazard, you don’t need to know much about potential weak layers or bed surfaces, but here’s my take on the problem. The ravines had a pre-existing instability problem that was demonstrated with multiple avalanches on Sunday. These slabs have had a couple days to settle down, but I don’t believe that’s sufficient to fully stabilize them. A very weak layer of snow over a crust was the problem on Sunday. This was not the case everywhere—some locations were wind scoured and stable. But the riming and graupel period at the start of the most recent snow with winds from a SW direction and lighter than they currently are makes me think that an easily triggerable weak layer may have formed over most aspects. Winds shifted to the W and slowly to the NW with increasing speeds, laying a denser slab on top of this weak layer. If areas have already avalanched, ongoing loading and reloading of the slopes will keep the hazard elevated.
- 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 8:20 a.m. Tuesday, March 31, 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