Avalanche Advisory for Tuesday, 2-21-2012

Expires 12:00 midnight, February 21, 2012

Tuckerman Ravine has MODERATE and LOW avalanche danger.  The Sluice, Lip, Center Bowl, and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The Lobster Claw, Right Gully, Left Gully, and Hillman’s Highway have Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features. The Lower Snowfields and the Little Headwall are not posted due to an overall lack of snow. Forecasts for these locations will begin when conditions warrant.

All forecast areas of Huntington Ravine have LOW avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features.

Stability is improving from day to day since the weekend snow stopped falling. Yesterday was a tough day to be in Tucks or up on Lion Head, due to almost constant blowing snow swirling around. The groups that did come out and braved the conditions seemed to be having a good time, with most of the traffic heading into Right Gully. Although there was a lot of snow being blown about, it didn’t build up into very reactive slabs. Rather, it would build to a critical point then release a small sluff down into lower angle terrain. This was going on everywhere from the Chute across to the Sluice. The dominant surface layer in these areas was a mixture of the sluffed-off snow and wind-effected snow. Digging pits was a futile exercise yesterday, since snow would fill them in just as quickly as I could shovel it out. But I was able to find the crust deeply buried with a light density layer above it, and above this is the aforementioned mixed surface layer. Overall depths of these layers is highly variable depending on your location. For example, where I dug in the Sluice the surface layer was about 70-80cm, the lighter layer was about 20cm thick, and the crust was 2cm. As mentioned, stability is getting better, but I don’t think it’s dropped enough that we can call any of the Moderate areas anything different today. Additionally, light winds may allow solar energy to rapidly warm the snowpack if clouds today do not materialize until later, which could lead to greater instability. Currently, the Sluice and Chute have lesser stability issues than the Lip and Center Bowl, but the degree of variability out there may put you into snow that is more unstable than anything I saw yesterday. As with yesterday, the areas of greatest concern are in the Lip and Center Bowl. If you trigger an avalanche today, it’s most likely to fail at the interface of the sluff/wind-effected layer and the lighter density slab below. There is generally good adhesion of the light density snow to the buried crust.

Huntington Ravine, Left Gully, and Hillman’s Highway all have similar conditions. You’ll find a lot of older surfaces. How do you know if it’s old? One key piece of evidence is a set of old bootprints that had the surrounding snow eroded out from around them. These things look like dinosaur spines from a distance, and they can be found in most of these forecast areas. Other than that, you’ll find strong stiff windslabs that make for good climbing conditions. You also might find areas of exposed old crust. This is likely to be found on S-facing slopes (such as below and near the top of Right Gully) and climbing it without crampons can be like trying to kick steps into a steel plate.

The brief sunny break in the weather will be coming to a close tonight. Some new snow is expected to fall overnight and into tomorrow, with unsettled and warm weather through the rest of the week. Keep your plans flexible and be sure to check the avalanche advisory before heading up into the ravines.

Please remember:

  • 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 7:45am. 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

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