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USFS Avalanche Bulletin
7:37 a.m., Tuesday, February 9, 2010
Tuckerman Ravine has MODERATE and LOW avalanche danger. The Lip, Bowl, Headwall and Right Gully have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Use caution in steeper terrain. Left Gully, Hillman's Highway, the Lower Snowfields and the Little Headwall have Low avalanche danger. Natural avalanches are very unlikely and human triggered avalanches are unlikely except in isolated pockets. Normal caution is advised. Huntington Ravine has LOW avalanche danger. Natural avalanches are very unlikely and human triggered avalanches are unlikely except in isolated pockets. Normal caution is advised. Today looks to be a fine day to be in the mountains. The temperature at Hermit Lake is already a balmy 26F (-3C) and the morning sun is beautifully lighting up Tuckerman Ravine. Winds are expected to further diminish during the day and any residual fog should burn off by the afternoon. Stability concerns that exist today stem from two events. The first was a 3.4" (8.5cm) snowfall back on Wednesday followed by strong winds Thursday. The second was about an inch (2.5cm) Sunday night. The former created a multi-layered snowpack in lee areas such as the Sluice, Lip, and Headwall. Other areas were scoured down after this event, and remain posted at Low danger. The more recent dusting was blown into the ravines on NW winds and has accumulated in thin patchy slabs on top of the preexisting surface. As I mentioned in yesterday's Advisory, this new snow wasn't enough to bump up the danger ratings, but where you find this newly developed slab you can expect it to be energetic and reactive. These are two adjectives we frequently use to describe slab properties, and they refer to how much potential energy a slab has and whether or not they have the potential to propagate a fracture. When a slab has stored elastic energy it is more likely to snap, or react, to the additional stress put on it by a person. One factor today that will work toward greater stability is solar gain on S-facing slopes; its effect dissipates some of the stored elastic energy and reduces the potential for a fracture to propagate. Remember though that it works from the surface downward so deeper instabilities may not be affected. The areas posted at Moderate have numerous layers and I do not expect solar gain today to be sufficient to eliminate the possibility of human triggered avalanches. The areas posted at Low danger today, namely Left Gully, Hillman's, and all of Huntington, have a lot of exposed hard rain crust with good stability. Climbing conditions on this surface are great, but be ready for a quick self arrest if you should slip. Also be watchful for isolated pockets of newly developed unstable slabs created from Sunday night's snowfall. The Lion Head Winter Route is open. It is a steep route and an ice axe and crampons are recommended for safe travel. The John Sherburne Ski Trail has variable conditions with some packed snow and long stretches scoured down to the rain crust.
PLEASE REMEMBER:
• Natural events such as avalanches are impossible to accurately predict in every instance. This Advisory is one tool to help you make your own decisions in avalanche terrain. It should be used along with safe travel techniques, snow stability assessments, an understanding of weather's effect on the snowpack, and proficiency in avalanche rescue.
• You should obtain the latest weather forecast before heading into the mountains. Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast.
• For more information, contact the U.S. Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center or Hermit Lake Shelters or the HMC caretaker at the Harvard Cabin. A new avalanche advisory will be issued tomorrow and this advisory expires at midnight.
Jeff Lane, Snow Ranger• Natural events such as avalanches are impossible to accurately predict in every instance. This Advisory is one tool to help you make your own decisions in avalanche terrain. It should be used along with safe travel techniques, snow stability assessments, an understanding of weather's effect on the snowpack, and proficiency in avalanche rescue.
• You should obtain the latest weather forecast before heading into the mountains. Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast.
• For more information, contact the U.S. Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center or Hermit Lake Shelters or the HMC caretaker at the Harvard Cabin. A new avalanche advisory will be issued tomorrow and this advisory expires at midnight.
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856
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U.S. AVALANCHE DANGER SCALE
LOW: Natural avalanches very unlikely. Human triggered avalanches unlikely. Generally stable snow. Isolated areas of instability. Travel is generally safe. Normal caution advised.
MODERATE: Natural avalanches unlikely. Human triggered avalanches possible.. Unstable slabs possible on steep terrain. Use caution in steeper terrain on certain aspects (defined in accompanying statement).
CONSIDERABLE: Natural avalanches possible. Human triggered avalanches probable. Unstable slabs probable on steep terrain. Be increasingly cautious in steeper terrain.
HIGH: Natural and human triggered avalanches likely. Unstable slabs likely on a variety of aspects and slope angles. Travel in avalanche terrain is not recommended. Safest travel on windward ridges of lower angle slopes without steeper terrain above.
EXTREME: Widespread natural or human triggered avalanches certain. Extremely unstable slabs certain on most aspects and slope angles. Large destructive avalanches possible. Travel in avalanche terrain should be avoided and travel confined to low angle terrain well away from avalanche path run-outs.
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