Posted 8:58, Thursday, February 17th, 2011
Tuckerman Ravine has both CONSIDERABLE and MODERATE avalanche danger. The Sluice, Lip, Center Bowl and the Chute have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.
Huntington Ravine has LOW avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features or extreme terrain.
The mid winter thaw has begun! The positive thing I can say is this thaw should be brief and not all that damaging to the mountain snowpack, but nevertheless heat and rain is never fun in winter. Driving up to Pinkham Notch this morning it was 12F (-11C) for a good part of my commute. An hour later at Hermit Lake it is 40F (4.5C)! Air mixing from the valley and up high should slow this rapid spike of mercury at the mid elevations however these temperatures will impact cold slabs today setting us on an instability trend over the next 24 to 36 hours.
Brian and I got into Tuckerman to see the effects of Tuesday’s big wind and snow. A sizable debris pile littered the floor with many very hard and icy chunks of hard slab as well as pieces of water ice, insinuating that the avalanche cycle stepped down into older hard slab. The mass and force impacted even deeper slabs causing them to fracture but not fail leaving behind a number of large “settlement cracks” some of which appear like crevasses. They were impressive and larger that I have seen in a long time. Check out a couple of the pictures posted yesterday on our website. We both felt this event would have produced a sizable crown line but not a piece of it could be seen as continued loading filled in the evidence. We believe the majority of the debris came from the right side of the Headwall near the Lip over to the Sluice. While examining all of this we poked around under Right Gully and the Lobster Claw and found plenty of cold facets beneath an eroding crust. In numerous locations this crust was at the surface and in others it was beneath slabs of varying thickness. We have been chasing and watching facets in different stages since the crust development a number of storms ago as cold conditions have prevailed over the past few weeks. This is the underlying cause for concern in this warm up. As slabs warm they will lose their tensile strength that is currently allowing them to bridge these varying pockets of facets. By affecting the temperature gradient in the snowpack, slab thickness over the crust has affected the development, size and relative weakness of these facets from snowpit to snowpit. Therefore, expect a high degree of spatial variability due to pockets of advanced facets under quite different thicknesses of slab. The instability will increase through the day as heat penetrates cold slabs, with areas reaching Considerable this afternoon and areas rated Moderate to reach into the upper end of the rating. The Sluice should be the first to reach Considerable today, due to its south facing aspect and the soft slabs I encountered yesterday. In summary, we have gone to a Considerable rating in the Sluice, Lip, Center Bowl, and Chute mostly due to the potential for natural avalanche activity due to weakening slabs over areas of advanced facets as we move through this warm weather and rain potential.
In Huntington Ravine the avalanche danger rating is posted at Low today. We believe natural avalanches are unlikely, but not impossible to occur over the next 24-48 hours. The definition for “Low” avalanche danger allows for avalanches to occur in isolated terrain features and/or extreme terrain which most of Huntington’s steep gullies qualify. Also anticipate some falling ice to cause an additional hazard.
- 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