Posted 8:40a.m., Thursday, February 10, 2011
Tuckerman and Huntington Ravines have MODERATE avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully to identify areas of concern.
As of early Thursday we continue to have no visibility with light snow falling on the mountain. About 30 hours ago, just after midnight yesterday morning, we had a temperature of -22F (-30C) and a peak wind of 104mph (168kph). This set up a scouring scenario in most locations punishing existing slabs and moving the 3.8” (10cm) of new snow and additional snow from above treeline down low in the majority of our terrain. Drifting exists on the Tuckerman Ravine trail from Pinkham all the way to Hermit Lake. As yesterday ticked by winds subsided down to 36mph (57kph) by early afternoon, all the while blowing new snow on to the recently scoured surfaces allowing some new slab to be created. Blowing snow came to a halt overnight even though winds had picked back up to around 80mph for a short period. The outcome today is a fair degree of spatial variability which will make it difficult to make good travel decisions due to fog and light snow limiting visibility to about 200 feet. Even though you may be on scoured surfaces where you are, you may not be on stable surfaces just ahead. Being familiar with the terrain and being mindful of which terrain gets loaded by west winds will be very helpful as I believe these strong lee deposition zones are where you will likely find unstable slabs. This is particularly true in Tuckerman’s strong lee forecast areas such as high in the Chute, under the headwall ice in the Center Bowl, and in the Lip and Sluice. Some of these locales may be on the upper end of the Moderate forecast rating. Expect some cross loading to have occurred in Right Gully and the Lobster Claw especially on the climber’s left side. Over in Huntington than in Tuckerman you should find more scouring due to the specifics of the terrain and the vortex effect of its narrow gullies. Any unstable slabs in the Huntington gullies are likely to be new since the 100+mph (160+kph) winds referred to earlier.
With the recent high winds and cold temperatures I would expect any hard slabs that exist to possess good elastic energy which would propagate a fracture easily if failure of the slab is initiated. This “snapping” release of energy would be most plausible in slab hardness between “pencil” and “1 finger” on the hardness scale. Thick hard slabs created by 100+ winds that are approaching “knife” hardness we dub “Steel Slab” and often bridge over weaknesses below and support a climber’s weight due to high tensile strength. These are often very difficult to get a boot edge into and require crampons for a travel as a reference point for you on the hardness scale. Generally speaking, you’ll find the best strength on the hardest, thickest slabs you can find, but you need to use more than general rules of thumb to navigate safely!
- 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.
- This advisory expires at midnight. A new advisory will be issued tomorrow.
Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856