This advisory expires at midnight, Monday 3-5-2012.
All forecast areas of Tuckerman and Huntington Ravines have Considerable avalanche danger today. Natural avalanches are possible; human triggered avalanches are likely. The only exception to this rating is the Little Headwall, which has Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features.
I guess it’s true what they say about weather being unpredictable at times on Mt. Washington. In the most recent instance, it worked in favor of those who want more snow, but against those who were looking to recreate in avalanche terrain today. Over the last 30 hours, the summit has recorded 6.5” (16.5cm) of new snow. Yes, that’s correct, six and one-half inches. Not only is the total depth remarkable and unexpected, but the density is incredibly light, coming in around 2%. If we hadn’t seen these flakes with our own eyes, we wouldn’t believe the accuracy of the measurement. But they were practically floating in the air like little helium balloons, so I’m a believer. Most of this snow fell between noon and midnight; winds during this time started very light and increased to their current speeds of around 40mph (65kph) from the WNW. A small amount of additional snow is expected to fall this morning.
Today’s stability concerns are primarily related to the new light density snow. It doesn’t require a strong wind to move this snow from one location to another (e.g. from the Alpine Garden into Central Gully). New soft slabs are being created and are growing as I type this advisory. Despite the trend for skies clearing today with high pressure, winds will continue to pick up and deposit the recent snow into steep slopes of both ravines, even after skies clear later today. Direct loading and cross-loading will be taking place in all forecast areas. Expect new slabs to be soft and very reactive to triggering, either from a person or from the increasing load of wind-transported snow. I want to emphasize that today’s Considerable rating is for both human triggered avalanches being likely as well as the possibility of natural avalanches.
The threat of avalanches today is real, and presents additional concerns. We are also thinking about the chances of an avalanche stepping down into slabs that existed prior to the new snow. Field work yesterday showed a spatially-variable snowpack, with some locations registering some frighteningly easy test results while other areas showed reasonably good stability at the surface. We can foresee an avalanche that does step down into older instabilities being quite large, and that conclusion was drawn even before we knew there would be another 6.5+” of snow about to be loaded onto the slopes. Overall, this is a complex snowpack that will require focused attention to navigate safely. To conclude, I recommend avoiding avalanche terrain until visibility improves, and then you’ll need to give some serious consideration to your objectives for the day. There are always options that don’t involve avalanche 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.
- Posted 8:35a.m. A new advisory will be issued tomorrow.
Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856