Posted 8:15, Sunday, January 09, 2011
Tuckerman Ravine: The Chute, Center Bowl, Lip and Sluice have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Hillman’s Highway, Left Gully, Right Gully and the Lobster Claw have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The Lower Snowfields and the Little Headwall are not posted due to a lack of snow.
Huntington Ravine: All forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanche are possible. The Escape Hatch remains not posted due to a lack of snow.
All forecast areas have bumped up a rating from yesterday’s ratings. This is based on the potential for new snow today and wind loading that will continue through the day and into tonight. The amount of new snow accumulation will determine how much instability will develop and I’ll warn you now that the forecasted snow totals are nothing to get too excited about. Before we jump into that, let’s focus on a reliable factor in today’s forecast: wind. The mountains will see increasing NW winds that are expected to reach steady velocities between 60 and 80 mph (96 and 129 kph) with higher gusts. These winds will do a great job at transporting any new snow into the Ravines and creating new wind slab. Right now there is about 1.5” (3.8 cm) of snow above treeline that is currently being blown into the Ravines and the forecast is calling for upslope snow showers to bring anywhere from a trace to 3” (7.6 cm) of new snow today. (I warned you!) The difference between a trace to 3” for our avalanche danger is significant. If we pick up 2-3” of new snow we think that new instabilities will develop to the point of being problematic for people travelling in avalanche terrain, especially in Tuckerman Ravine where natural avalanche may be possible. Seemingly insignificant amounts of new snow can be deposited into feet of wind slab in strong lee areas. A similar type of event occurred last week and there are still wind slabs lingering in Tuckerman Ravine that are anywhere from 6” to 18”+ (15 to 46 cm) deep. All existing wind slabs and those that are forming today will be sitting on a slick bed surface that is a dominant feature on the mountain. This is a souvenir from a recent warm up that ate a lot of our already meager snowpack. When cold air returned it turned the snowpack into an icy mass. This is a challenging surface for new snow to stick to and may provide a great bed surface for avalanches. Sloughing can also be expected today as new snow is transported into the steep snowfields and gullies of the Ravines. If you are heading into avalanche terrain today be aware that the avalanche danger will be increasing through the day.
If you are going to be in steep terrain you need to be proficient with crampons, an ice ax and self arrest skills. It is alarming how fast a person can pick up speed if they fall on the icy snow. Rapid self arrest is essential if you slip on this surface. The Shurburne Ski Trail has thin cover. Expect earth poking through the thin snow and ice cover along the trail.
- 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