Posted 8:28a.m., Thursday February 3rd, 2011
Tuckerman and Huntington Ravines have CONSIDERABLE avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Some dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route finding and conservative decision making is essential. The only exception to this rating is the Lower Snowfields and the Little Headwall which have Moderate avalanche danger.
So the big question is what DIDN’T avalanche during yesterday’s storm? Fracture lines or debris can be seen in most locations in Tuckerman and we’ll get a closer look into Huntington later this morning. Gully 3, Dodge’s Drop, Hillman’s, the Duchess, Dead End Gully, Left Gully, blah-blah-blah I would say most angled terrain above 30 to 35 degrees had an avalanche cycle. Hermit Lake received 15” (38cm) of snow over 48 hours while the summit is reporting 11” (28cm) that fell with moderate wind velocities from the W, S, and mostly from the SE during the majority of Wednesday’s snowfall. Some low hanging fog hides the Ravines from time to time, but this should blow out to provide good visibility. When the slopes pop out from the clouds you will see smooth snow with very few crisp fracture lines showing or wind effected snow. This is because since the last round of avalanches new snow deposition has reloaded previous bed surfaces. Although wind speeds are expected to increase in the afternoon to about 35mph (56kph) from the N and NW new loading should be somewhat limited today, but certainly something to keep an eye on. If loading picks up I would be most suspect of S and SE facing aspects. New snow densities on the summit hovered around 6% with the last couple of inches being even lighter. This snow will be more tempted to move with light winds today than our average densities around 9-10%. Therefore natural avalanches are possible under the Considerable rating, but the main rationale for today’s rating is the concern for human triggers. This stems from light summit snow densities being loaded into soft slabs under cold conditions allowing the snowpack to retain it’s elastic energy. I would expect the fracture and failure of slabs to have good propagation propensity, which is bad for us. Don’t let the relatively calm conditions and the blue skies lull you into ignoring what Mother Nature is holding if you step back and take an objective look. You may find some locations within a forecast area to be below the Considerable rating, but as you get into steeper terrain and high in elevation near the start zones this will likely change. Being conservative with your terrain choices and giving the snow some time to consolidate is always prudent after a storm, particularly one that came in with light to moderate wind speeds. Saying this you may have to wait for while because winds will ramp up tonight and may push over 70mph (113kph) from the west tomorrow. This will generate a significant loading event with a new concern for natural avalanches justifying a Considerable forecast or even High for some areas. We’ll see how the weather forecast plays out. This event will be followed by another, albeit more subtle, storm on Saturday/Saturday night. Check back often and stay on your toes it could be an interesting few days.
- 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.
Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856