Posted 8:20a.m., Wednesday, March 2, 2011
Tuckerman Ravine has CONSIDERABLE, MODERATE and LOW avalanche danger today. Center Bowl, Lip, Sluice and Right Gully have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Hillman’s Highway, the Lower Snowfields, Left Gully, the Chute and Lobster Claw have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The Little Headwall has Low avalanche danger. Natural and human-triggered avalanches are unlikely.
Huntington Ravine has LOW avalanche danger today. Natural avalanches are unlikely and human-triggered avalanches are possible. Watch for unstable snow on isolated terrain features.
Hard slabs, soft slabs and the potential for additional wind loading are the three main issues today. It has been a dynamic few days and the snowpack is complex. Monday’s storm system deposited increasingly dense snow on the mountain and was accompanied by increasing winds that were out of the S, W and NW respectively. This resulted in numerous natural avalanches in both ravines. The winner for the best runner from this event was Hillman’s Highway with Left Gully in close second. Hard slabs left over from this event exist in many areas and fall within the Moderate rating. Stability tests performed yesterday showed failure on weak layers within these slabs to be around 60 cm deep on a less consolidated layer. Extended column tests showed a reluctance to propagate across the weak layer leaving us to believe that it would be difficult to get one of these to go but if it did it would probably be a major problem for the instigator. The second issue you will find today is soft slab (1 finger to 4 finger) that developed when temperatures fell on Monday night and Tuesday morning and light density snow accumulated on the mountain. While this didn’t add up to much on the storm boards, NW winds did a great job at depositing it into some specific locations, creating new soft slabs that are several feet deep in places. The most notable places we found these are in the Lip, Sluice and Right Gully in Tuckerman Ravine. I think this development was also responsible for instability that a skier found in the Gulf of Slides yesterday. He triggered a sizable avalanche in a start zone and was caught and carried down the entire path. It seems that the fracture line ranged between 1 and 3 feet deep and propagated about 400′ across the slope. Lucky for him he was able to fight his way back to the surface as it came to a stop and escaped uninjured. YIKES! You may also find some of these softer slabs in Huntington Ravine, though much of Huntington did get scoured out by strong winds. Some places to look out for in particular are in the start zone of Damnation, the middle of South Gully and the Escape Hatch. The third issue today is new snow and wind loading. New snow is currently falling but is only expected to accumulate to around one inch (2.5 cm). Today’s summit winds are forecasted to be out of the west between 70 and 90 mph (113 and 145 kph) before decreasing slightly to 60 to 80 mph (97 to 129 kph) later today. These winds will transport any new snow into the ravines and may create new snow stability issues. Given the light totals, we don’t think this will have a major impact on the avalanche danger but we do think it will have some. Expect new wind slabs to form today, even in areas forecasted at Low. (Remember, Low doesn’t mean no avalanche danger.) If we exceed the forecasted snow totals expect increasing avalanche danger that could push forecast areas into the next higher danger rating. The areas posted at Considerable are the ones most likely to collect problematic amounts of new snow and they harbor the most soft slab that I mentioned above. In conclusion, today’s is not a straight forward day as far as the snow pack goes. If you plan on being in avalanche terrain you should have solid snowpack evaluation skills, along with good route finding and safe travel techniques.
- 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