Posted 7:45a.m., Thursday, March 24, 2011
All forecast areas in Tuckerman and Huntington Ravines have Moderate avalanche danger today. Natural avalanches are unlikely and human-triggered avalanches are possible. The only exception to this rating is Tuckerman’s Little Headwall which has Low avalanche danger. Natural and human-triggered avalanches are unlikely in this area.
The good news is that today’s weather is not expected to have a significant impact on overall snow stability. The bad news is that we still have lingering issues from the snow that fell at the beginning of the week. Scattered snow showers are forecasted for today but they’re supposed to be light and spotty with little measureable accumulation. We’ll likely spend the majority of the day in the clouds with difficult light for picking out visual clues. Winds are expected to stay below 25mph (40kph) except for an occasional gust so transport of snow will be limited. They will wrap counter-clockwise from where they now sit out of the E and eventually land in the NW. This scenario may provide just enough wind from the correct direction to cause the development of very light density windslab high in the start zones of slopes with S and SE aspects. It may look like powder but if it breaks apart in chunks it is cohesive enough to fail and fracture as a slab. Although the new snow may create small localized issues what drives today’s forecast is really the existing areas of windslab that are fairly widely distributed. As a quick recap the mountain picked up about 6” (15cm) of cold dry snow at the beginning of the week. Moderate winds from the S accompanied the snow’s onset before they slid around through the W and then the NW, effectively loading all forecast areas. The soft slab created was laid down on top of a slick crust in many places so adhesion at this interface was poor. Temperatures have remained seasonally cold so settlement and bonding have been slow to occur. Field observations yesterday showed slabs with a significant amount of energy that was still willing to propagate a fracture. Within the Moderate rating there is a range of conditions to be found in the forecast areas. The primary concern is for human-triggered avalanches on E to SE aspects such as the Center Bowl through the Sluice in Tuckerman and O’Dell through Yale in Huntington. These areas developed the thickest windslab from the last storm event and will be in the direct lee of whatever loading occurs today. As you move away from these aspects you begin to find areas that provide more reasonable options for travel. As an example Hillman’s Highway has a fair amount of old surface showing and the new snow is easily identifiable. I believe that you can still have a good time out there if you keep your plans flexible, practice safe travel techniques and continually assess stability as you move through the terrain.
The thick icy crust that provides a poor bonding surface for the snow also creates trouble for visitors where it isn’t buried. The cramponing may be top notch but the potential for sliding falls is also high where the crust is exposed. Ice axes are used to self arrest yourself in such conditions and if you don’t have one you have little hope for stopping a sliding fall once it’s begun. Crampons will get you up there but the ax will make sure you don’t come rocketing down. And as a quick reminder, snowshoes have no place in steep terrain! They may have “crampons” on the bottom but they are not designed for anything more than 15 or 20 degree slopes. Last week we had one incident that resulted from an attempted snowshoe ascent of Right Gully. Come prepared with the correct equipment and skills for the conditions and terrain!
- 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.
Justin Preisendorfer, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856