This advisory expires at midnight, Tuesday 3-6-2012.
Tuckerman Ravine has Considerable and Moderate avalanche danger. The Sluice, Lip, Center Bowl, Chute, and Left Gully have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. The Lobster Claw, Right Gully, Hillman’s Highway, and Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely; human triggered avalanches are possible. The Little Headwall has Low avalanche danger. Natural and human triggered avalanches are unlikely.
Huntington Ravine has Moderate and Low avalanche danger. Central and Pinnacle gullies have Moderate avalanche danger. Natural avalanches are unlikely; human triggered avalanches are possible. All other forecast areas have Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features.
It’s pretty amazing what a small amount of moisture in the atmosphere can accomplish. Two nights ago, an unexpected upslope snow event took place, laying down about 7” of very light density snow across the higher terrain. This has since been subjected to W to NW winds blowing 35-50+mph (56-80kph), which has moved a lot of snow into Tuckerman Ravine. Across the upper rim of the ravine, the winds have scoured away the new snow, pushing it into stronger lee areas such as below the Lip, below the ice in the Center Bowl, and above the narrows of Left Gully. Other locations have also accumulated a significant amount of snow; the areas mentioned are just some of the most notable ones. This morning, skies are clear and temperatures cold. The NW 50mph (80kph) winds are currently at the upper end of what they were forecasted to be, and due to the winds there is a consistent ground blizzard bringing additional snow into Tuckerman. Today’s Considerable ratings are in large part due to the threat of naturally-triggered avalanches, but we are also thinking about how it would be likely for a person to trigger an avalanche in these newly developed slabs. In addition to the most recent snow, field work over the weekend gave us some concerns about underlying stability in the 12” snowfall from last Thursday. Recent weather has been preventing that dry, light snow from stabilizing in many areas.
Huntington Ravine was affected differently by the new snow. The northern gullies (North, Damnation, and Yale) were mostly scoured down. This is unusual with wind speeds being on the lighter side, but with such light density snow, it is not unreasonable. Central and Pinnacle were obscured by constant plumes of blowing snow. We suspect less scouring took place here than the northern gullies, but the airborne snow prevented us from confirming this. Odell, South, and Escape each have some localized areas of concern, but these are small enough to be considered “isolated terrain features.” If you pay attention in there, you can stick to areas with old surface or a thin veneer of new snow on top of the old surface. However, in the isolated areas you may find unstable new slabs that can avalanche underfoot as well as hard wind slabs that are thin enough to crack and avalanche.
Solar energy today might be a double-edged sword. One the one hand, it can help snow become more stable, if the energy it provides is strong yet gentle. On the other hand, if it’s too strong and not gentle enough, the stability trend can quickly stop and the snow can rapidly become unstable. Southerly-facing slopes will receive the most solar gain, while E and N facing slopes won’t be affected much. The next couple days are looking pretty warm, with temperatures heading above freezing all the way to the summit. Our field work today will be focused on how this might impact stability in the next couple 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.
- 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