This advisory expires tonight at 12:00 midnight.
All forecast areas of Tuckerman and Huntington Ravines have CONSIDERABLE avalanche danger today. Natural avalanches are possible and human-triggered avalanches are likely. Cautious route-finding and conservative decision making will be essential today.
AVALANCHE PROBLEM: Wet slabs and loose wet avalanches will be the threats today. It doesn’t take an advanced degree in avalanche science to recognize the issue today. Warm temperatures and rain are in the forecast, coming immediately on the heels of several inches of new snow. This will bring elevated avalanche danger to all areas, but the greatest concerns will be in locations such as the Lip, Center Bowl, and Chute. The floor of Tuckerman Ravine is in the path of avalanches from these areas.
WEATHER: Temperatures have already begun to creep toward and even exceed the freezing mark at most elevations on the mountain. It won’t be long before we are in a period of pure rain, without any “wintry mix” to speak of. Add the strong S winds forecast for today and you’ve got a pretty soggy, ugly winter day. This morning the Hermit Lake snow plot had 5.7″ of new snow, with the top inch or so being saturated wet. Rain will continue to fall throughout the day with winds increasing. Eventually, a cold front will pass and temperatures will begin to fall back to normal and precipitation type will switch back to snow, but this is likely not taking place until well after dark.
SNOWPACK: There are a few things going on in the snowpack worth considering. First, the new snow that fell at the onset of this storm was accompanied by winds from a general southerly direction. This would have directly loaded N-facing slopes and cross-loaded E-facing slopes, increasing the depth of new wind slabs in areas such as Left Gully or Odell Gully. Second, there are the previously existing hard slabs sitting in various places, mostly in areas sheltered from W and NW winds, such as the Sluice, Lip, Center Bowl, and Chute. These had good strength but were sitting on a layer of weak snow. Third, a good benchmark is the Feb 3-4 rain crust. I doubt today’s rain will affect this crust layer or anything below it, but it may serve as a convenient bed surface for today’s avalanche activity.
Both the newly developed wind slab and the previously existing wind slab will be increasingly unstable today as rain overtakes the mountain. New slabs will be the first to release. The older slabs may hold in place, or the overrunning slab may provide enough force to pull these out as well. Wet avalanches are a dynamic process and are notoriously hard to predict with field assessments. Poor visibility will also limit the information available to you. In my opinion, it’s a good day to follow the terrain advice given when we have high avalanche danger: “travel in avalanche terrain is not recommended.”
- 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 7:55a.m., February 16, 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