Avalanche Advisory for 4-8-2013

This advisory expires at 12:00 midnight tonight.

Tuckerman Ravine has MODERATE and LOW avalanche danger. The Sluice, Lip, and Center Bowl have Moderate avalanche 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, but watch for unstable snow in isolated terrain features.

Huntington Ravine has LOW avalanche danger. Natural avalanches and human triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

Our snowpack has good stability in most areas. Some important exceptions exist. The first is very steep (40+ degree) slopes in lee areas of the 18 hour spell of high NW winds on the 5th and 6th. The Sluice, the Lip and Center Bowl are the most obvious examples in Tuckerman though smaller areas exist in Huntington in Central, Pinnacle and Odell.  These slabs could be reactive even after skier traffic especially if they lose strength due to warming.

Deeper slab instabilities beneath the firm snow are also on the radar. This slab is thick and strong in many areas but could possibly react to a heavy trigger like ice or rock fall or a head over heels tumbling fall. It is also possible for this slab, which is sitting on an old melt freeze crust, to be triggered at a thinner, weaker spot in the  slab.  This layer is worth watching carefully today and moving forward due to the severe consequences of being caught in a thick, hard slab avalanche like the one recently in the lower snowfields.

Another problem is the areas beneath steeper slopes where sluffs have piled up deeply such as beneath the Chute, Duchess and possibly Central Gully.  Triggering these is also difficult though certainly not imposssible.  The balance between strength and the weight of the slab is hard to calculate.  Exercise safe travel techniques in these areas.

The final issue under discussion is the solar gain on the snowpack today.  Wet, loose slides may become an issue on or below sunny aspects and could gain enough size and speed to be a real problem and may even trigger the deeper instability.

Our Low rating is NOT meaningless.  We still have a winter snowpack, not an isothermal springtime one. The transition between dominant weather patterns, specifically heating of the snow, adds complexity to forecasting and field assessments so be “heads up” out there. These are the kind of avalanche problems that can surprise you and it is another reason why safe travel techniques and proper safety equipment are always warranted.

Huntington Ravine has been holding up well for ice climbing, but this may start to change as temperatures warm this week. Currently most slopes are either scoured or wind-packed and have good stability, but watch for those pesky isolated pockets in sheltered locations. Last night was the final night of the season for the Harvard Cabin.  Camping at the Harvard Cabin is not permitted.

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 8:05a.m., April 8, 2013. A new advisory will be issued tomorrow.

Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713  TTY (603) 466-2856

2013-04-08 Print friendly