Posted 8:20a.m., Sunday, February 27th, 2011
Tuckerman Ravine has Considerable, Moderate and Low avalanche danger. The Chute, Center Bowl, Lip and Sluice have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Hillman’s Highway, the Lower Snowfields, Left Gully, Right Gully and Lobster Claw have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The Little Headwall has Low avalanche danger. Natural and human triggered avalanches are unlikely.
Huntington Ravine has Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.
There are two primary stability issues to focus on today. The first pertains to wind slabs that are left over from Friday’s snow storm that caused several natural avalanches in both Tuckerman and Huntington Ravines. The second is new snow that will continue falling into the afternoon and the potential for this new snow to form soft slabs that could push a number of areas to the upper end of their forecasted ratings. Starting with the first concern I mentioned, Friday’s storm brought between 6 and 8.5″ (15 and 21 cm) of snow to the mountains and it was accompanied by winds that shifted counter-clockwise from the SE to the W. Wind transported snow created unstable wind slabs and natural avalanches occurred in many of our forecast areas. Ongoing wind loading from west winds continued into yesterday leaving wind slabs behind of varying density and size. These wind slabs fall within the Moderate rating and it is possible you could cause one to fracture and fail resulting in an avalanche. These can be found in just about every forecast area with the Center Bowl, Lip and Sluice being the most unnerving representatives of this stability issue. Some areas, particularly in Huntington, have more spatial variability so good route finding skills can provide you some reasonable alternatives to climbing on this suspect snow. That being said, limited visibility will make it difficult to pick out a good line.
The second stability issue will be developing as the day progresses. The formation of touchy soft slabs is possible today as winds from the SW shifting to the W between 10 and 25 mph (16 and 40 kph) gently transport new light density snow into the start zones and other lee areas of the ravines. These new slabs could be pretty reactive to people making them easy to trigger and cause an avalanche. We are expecting up to 2″ (5 cm) of new snow today which makes us comfortable with many areas being posted at Moderate. If we exceed the forecasted snow totals some areas posted at Moderate may push into the Considerable rating due to the potential for these new slabs to avalanche on their own. This is a key piece of bulls-eye information you will need to monitor if you plan on being in avalanche terrain today. Either way, expect to find a variety of snow out there that is waiting for you to test the balance between strength and stress of the snowpack. The ability to evaluate snow stability and employ safe travel techniques will be important for anyone traveling in avalanche terrain today.
A significant storm is lined up to provide us with a messy Monday. Accumulating snow is forecasted to give way to freezing rain and possibly rain tomorrow. Expect this miserable weather to be complimented by elevated avalanche danger in both ravines.
- 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.
Brian Johnston, Snow Ranger
USDA Forest Service, White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856