This advisory expires at 12:00 midnight, February 25, 2013.
Tuckerman Ravine will have CONSIDERABLE and MODERATE avalanche danger today. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. Lobster Claw, Right Gully, Sluice, the Lip, Center Headwall have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Chute, Left Gully, Hillmans Highway, Lower Snowfields and Little Headwall in Tuckerman have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.
Huntington Ravine has MODERATE avalanche danger today. Natural avalanches are unlikely and human triggered avalanches are possible in all forecast areas. Evaluate snow and terrain carefully to identify features of concern.
It is important to note that low visibility will challenge your ability to perform snow stability evaluations on the mountain today as it has challenged ours. What we know about current avalanche concerns is developed from weather observations. The key information is that we received 6 inches additional new snow on light winds from midnight to midnight yesterday with another ½” from midnight to 6am today. Remember that 3” of snow fell prior giving us almost 10” of snow to deal with. Winds also increased for a period last night. So, several conditions lead us to formulate the ratings that we have today.
- New snow has accumulated most everywhere in our forecast area which has created a widespread thick soft slab of varying thickness laying over softer, weaker snow deposited earlier in the storm.
- Wind gusts increased during the overnight and morning hours today to a point where wind slabs of increasingly dense snow have formed in the higher start zones of our gullies as well as in other high, wind sheltered terrain features. These wind gusts came from the North and transported snow from drifts that were formed earlier yesterday when the wind was from a more southerly direction. The snow was light enough to be carried by these moderate winds.
- A slippery interface exists on south facing aspects in the form of a sun crust which formed on Friday. This sun crust will make for poor bonding of the new snow and will form the bed surface for any avalanches triggered in Lobster Claw, Right Gully, the Sluice and the Lip. South facing gullies in Huntington have a similar crust but new snow there did not accumulate in the upper start zones to as great a depth as in Tuckerman. Where this poor bonding surface exists in smooth areas of older snow, sensitive slabs may exist on fairly low angle slopes. I would be heads up in areas such as the approach to Right Gully and the slope beneath Harvard Bulge below Yale and Damnation buttress.
- Though the forecast is for a cloudy summit today, filtered sunlight through thin cloud cover can create a greenhouse effect which may warm the slab just enough to reduce its strength and lead to failure. The same process would make it more likely for slabs to be triggered by a skier or climber. The sun is currently barely obscured and it is bright outside at Hermit Lake and has been for half an hour which leads me to this concern.
Though the overall trend now is moving towards stability due to diminishing winds and no current snowfall, a lot of factors are at play today which can change this. Don’t let the calm winds and warm temperatures lure you into complacency.
- 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 8:45 2-25-2013. A new advisory will be issued tomorrow.
Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2817