Avalanche Advisory for Tuesday, 4-9-2013

This advisory expires at 12:00 midnight tonight.

Tuckerman and Huntington Ravines have Considerable avalanche danger today. Natural avalanches are possible and human triggered avalanches are likely. The only exception to this rating is the Little Headwall, which has Low avalanche danger. Natural and human triggered avalanches are unlikely in this area.

Springtime on Mt. Washington brings all types of weather…sun and warmth (yesterday), cold biting wind (Saturday), snowstorms (last Tuesday), etc. Today we are getting my least favorite type of spring weather event, rain and fog. This is the kind of weather that makes me ask “Really? This is really what I want to do today?” So if you’re reading this advisory from the relative warmth and dryness of the caretaker’s cabin entryway, thinking about heading farther uphill, this advisory’s for you.

Rain has the ability to trigger avalanches. As it saturates the upper snowpack, it breaks down bonds between snow grains and decreases the strength of the snow. As more rain falls, the water begins to percolate in channels downward through the snowpack. This continues until it hits something that it can’t flow through, such as a layer of ice buried beneath the snow. When this happens, the water acts as a lubricant between the weakening snow above and the slippery icy layer below. All the while, the rain is adding additional load (i.e. weight) to the snowpack. This is one mechanism to initiate a naturally triggered avalanche, and is what I can foresee taking place in some locations. The gullies of Huntington have a lot of locations with snow on top of water ice; other locations have snow on top of rain crusts that can behave similarly.

The entire process described above doesn’t need to play out in order to have increasing avalanche danger. This is what I expect to take place in much of Tuckerman today. The issue that raises the red flag for us is the buried weak layer sitting between a weak crust and a hard slab. I don’t think we’ll get enough rain to fully saturate the hard slab in many areas, nor is the crust thick and strong enough to act as a complete barrier. So the concerning factors are the increasing load on the snowpack combined with decreasing strength of the slab. This leads us to the conclusion that naturally triggered avalanches are a possibility today and their is an increased probability for human triggered slides, hence the Considerable rating. The human triggered piece of the puzzle will be greater in areas with thinner hard slab. In today’s situation, the ability to effectively assess stability using common tests  is diminished. You will need to be very alert, use very cautious route finding, and make conservative decisions today. Otherwise you’ll just be rolling the dice.

Huntington Ravine had been holding up well for ice climbing, but this is starting to change as temperatures warm. Expect some rock and ice fall to occur this week. The Harvard Cabin is closed for the season. Camping at the Harvard Cabin is not permitted.

Currently the Tuckerman trail from Pinkham up to Hermit Lake is still covered with snow and ice all the way to the bottom. If the weather forecast doesn’t change, this may not be the case come next weekend. There are several thin spots between the start and where the Boott Spur trail departs from the Tuck trail, above here should hold up well fora while.

Please Remember:

  • 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 at 8:00a.m., April 9, 2013. 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

2013-04-09 Printable