Avalanche Advisory for Wednesday, March 25, 2015

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Moderate and Low avalanche danger. The Sluice, Lip, Center Bowl, and Chute have Moderate danger. Natural avalanches are unlikely and human triggered avalanches are possible. All other forecast areas have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

All forecast areas of Huntington Ravine have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

AVALANCHE PROBLEM: Aging wind slabs are the number one problem today. These began forming on Saturday night and didn’t stop growing until Monday morning when winds slowed. As with the past two days, the primary concerns are in the middle of Tuckerman, from the Sluice across to the Chute. The main issue is in the uppermost layer of the snowpack, which varies in depth but is generally at least 12” deep (30cm). Large avalanches can be produced from these locations. As you enter the floor of the bowl, you will be standing on old avalanche debris from previous avalanches that are smaller than what can be expected currently. Don’t assume the rocks in the floor are out of the range of the avalanche potential!

WEATHER: There is some weather coming in starting tonight, but for most of today, the weather will not affect snow stability to any great degree. Expect winds to be shifting to the south and increasing in speeds. Some light snow or mixed precip may fall this afternoon and evening, but accumulations will be light. The fun stuff will come on Thursday as a warm front surges toward us, bringing rain all the way to the summits.

SNOWPACK: A good portion of the terrain in Tuckerman and Huntington is very firm wind-hammered surfaces. These offer good stability, but not great skiing or riding conditions. If you’re heading into one of these Low rated areas, the climbing will be easier and safer if you have an ice axe and crampons.

In the Moderate rated areas, the upper snowpack is predominantly 1F to 4F hardness windblown slab. Beneath this is a thin layer of new snow that fell prior to the winds ramping up in speeds on Sunday and loading the new slab on top. This weak layer is now buried under the aforementioned slab and waiting for a trigger. Fortunately, the upper slab does have a fair amount of strength to it, so we’re falling short of thinking human triggered avalanches are likely (which would warrant a Considerable rating.) In fact, these are the conditions where you could see several people ski or ride a slope without triggering an avalanche. This certainly does not imply the slope is stable, just that it’s not a hair-trigger Moderate. I can envision a situation where several people skiing the slope could actually be cutting apart the strength of the upper slab, making it a little less stable with every set of tracks. The snow quality in these areas is carvable and alluring, especially compared to the quality you’ll find in the Low rated areas, but don’t allow your desire to have fun influence your risk assessment. Make quality snow stability assessments, think hard about your decisions, and be prepared for the worst case scenario. In these conditions an avalanche could easily kill you, and that would certainly ruin the fun you and your buddies came for.

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 6:30 a.m. Wednesday, March 25, 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

2015-03-25