Avalanche Advisory for Saturday, April 25, 2015

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger today. Natural avalanches are possible and human-triggered avalanches are likely in The Sluice, Lip, Center Bowl, and the Chute and are rated CONSIDERABLE as a result. All other areas have Moderate avalanche danger. Natural avalanches are unlikely but human-triggered avalanches are possible in Lobster Claw, Right Gully, Left Gully, Hillman’s Highway, and Lower Snowfields. The only exception is the Little Headwall which has Low avalanche danger but has some open holes in the waterfall area. Use care if riding this and start from Connection Cache down the trail from the floor of the Ravine. Huntington Ravine is under a General Advisory. You will need to do your own snow stability assessments when traveling in avalanche terrain in Huntington.

AVALANCHE PROBLEM: A surprising amount of recent new snow and ideal wind speeds for loading lee slopes have built Wind Slabs in Tuckerman Ravine. These wind slabs are likely to generate medium to large size avalanches, sensitive enough to be triggered by a skier, rider or climber and will have the ability to propagate a crack a long distance. They will be more than capable of burying a person and killing them by suffocation or trauma. This is true in Moderate as well as Considerable rated areas. Lower angle areas with bushes and rocks may be less prone to avalanche but could still be swept by debris from avalanches starting higher in the terrain. Once you pass the first aid cache on the way into the Ravine, 15 minutes up from Hermit Lake, you are in avalanche terrain.

WEATHER: Low visibility is expected to be a problem all day. Flat light and fog will make identification of critical snowpack details, as well as spotting people in avalanche start zones above you, a significant challenge today. A trace to 2” (TR to 5 cm) of new snow will further complicate things and add to our stability concerns. Cloud cover will keep temperatures below freezing even as the ambient temperature rises to the low 20’s F on the summit. Expect a windy, cold winter-like day.

SNOWPACK: A grainy and textured bed surface of refrozen corn snow allowed the initial new snow falling on it a few days ago to bond. The snow just above is our weak layer due to it being deposited during very low winds. Think of this layer as generally intact snowflakes with weak arms trying to hold the overlying firmer wind slab in place. These flakes are currently quivering and shaking due to the strain of holding up the wind slab which is likely to be thick in many of our start zones. In total, 9” (23 cm) of new snow built this wind slab on 40-60 mph (65- 95 km/h) W and NW winds. The wind slab is soft enough to crack easily and depending on the location will be finger to pencil hard. We have not been able to verify what has naturally avalanched, what has potentially been reloaded and what is harboring the thickest wind slabs. Because of this we need to assume all locations still possess substantial hazard and instabilities. Looking ahead, keep in mind the weakening affect that heat and filtered sunshine will have on this slab.

OTHER HAZARDS: The typical springtime hazards have become less of a problem with the recent freeze-up. You should be aware of the potential of falling ice, crevasses, and undermined snow. The best you can do to mitigate the risk from these objective hazards is to avoid them, especially during times when they are more probable. Hazards such as emerging crevasses and holes in the Little Headwall may be hard to recognize today and tomorrow, due to being hidden by new snow. The greatest hazard today is the threat of avalanches, and debris running on to the floor of the Ravine. The Sherburne Ski Trail will have the lower section closed. You can ski (mostly) to the #3 crossover, then pack up the skis for the 3/4 miles of hiking down the Tuckerman Ravine Trail.

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 Mount Washington Volunteer Ski Patrol, or the AMC at the Pinkham Notch Visitor Center and Hermit Lake.
  • Posted 8:30 a.m., Saturday, April 25, 2015. A new advisory will be issued tomorrow.

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

2015-04-25 Print friendly