This advisory expires tonight at 12:00 midnight.
All forecast areas of Tuckerman and Huntington Ravines will have Considerable avalanche danger. Dangerous avalanche conditions exist. Natural avalanches are possible and human triggered avalanches are likely. Careful snowpack evaluation, cautious route-finding, and conservative decision making are essential. The only exceptions to this are the Little Headwall and Lower Snowfields which have Low avalanche danger. Natural and human triggered avalanches are unlikely in these locations, watch for unstable snow in isolated terrain features and runouts from paths above the Lower Snowfields.
AVALANCHE PROBLEM: Avalanche danger will be on the rise today as wind slab will be forming today on top of a very weak layer of unconsolidated snow. These will form in all forecast areas, although locations with SE aspect will rise most quickly. By the end of the daylight hours, I expect avalanche activity to be testing the upper limits of the Considerable rating due to the threat of both naturally triggered avalanches and the likelihood of human triggered avalanches.
WEATHER: The most recent storm deposited 11” (27.5cm) of light density snow. The distribution was fairly even across all elevations from Pinkham up to the summit, but settlement over the last three days has led to the storm board totals being in the neighborhood of 6-8”. Thanks to lighter-than-usual winds, much of this snow is sitting right where it landed, including in the alpine zones above both ravines. We are expecting increasing wind speeds from the NW, rising to 35-50mph (55-80kph).
SNOWPACK: The steady increase in wind speeds today is going to drive the avalanche danger up the scale. There is a lot of snow sitting above treeline that should easily be transported by 35-50mph wind. Currently, most of the terrain is blanketed with a layer of loose unconsolidated snow. In some places this may only be 3-4” deep and in other areas it is much deeper. Yesterday, 3” of dust on crust led me to want crampons on my way up toward North Gully (seriously!). This blanket of weak snow will be buried underneath slab with increasing density, i.e. the classic “upside down snowpack.”
Some locations have multiple layers of 1F slab under the new snow. I believe these formed on Friday, the last day winds topped 50mph. These layers, at least where I saw them, had poor structure but good strength. I mention them because I want you to know that getting an early start will help you avoid the increasing danger, but you’ve still got to keep your awareness up for existing instabilities.
- 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 8:00 a.m. February 10, 2015. 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