Posted 9:15 a.m., Saturday February 5th 2011
Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. The Lip, Chute, and Hillman’s Highway have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Expect heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully. Anticipate the potential for large avalanches in isolated areas. The only exception to this rating is the Little Headwall which is Low.
Huntington Ravine has MODERATE and LOW avalanche danger. Central, Pinnacle, Odell, and South have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. All other forecast areas have Low avalanche danger. Watch for isolated pockets of instability in these areas.
It’s been an interesting couple of days since Wednesday’s storm with a lot of avalanche activity, some locations sliding repeatedly. Most notably are Hillman’s Highway and Dodge’s Drop which ran again yesterday morning due to high winds reaching 65-75 mph (105-121kph) and the main Tuckerman Center Bowl that avalanched this morning between 8:45 and 9:00am. Plumes of snow have been the norm now for over 24 hours as some loading continues up high in several start zones. In general new loading should remain light across the mountain though a few locations of note will be easy to pick out this morning as blowing snow swirls over the ridge. Since yesterday some strong lee areas have continued to grow, most notably in the Tuckerman Lip and under the Headwall ice. Obviously under the Headwall ice these slabs became overwelmed this morning with a large natural avalanche propagating very well in new hardslab. This is a substanial piece of information and should be the main driver for decisions today. Natural avalanche activity is a clear indication that unstable slabs exist. Taking these facts as well as my field experiences yesterday with settlement cracks in hard slab, I believe in areas posted at Moderate we are on the absolute upper end of the ratings defintion particularly in Tuckerman. I would have the most conern about the hang fire above the new avalanche in the Center Bowl and everything from the Chute to just past the Lip.
The main issue we are dealing with is a layer of weak low density unconsolidated snow that fell during a period of very low wind following the main storm. Because of this I have some concern that if slabs fail under new load, like you, they could propagate into a sizable avalanche. In some locations where hard slabs are thick I believe they have bridged over the weak layer of unconsolidated snow, but as you move to the thinner edges it may become easier for your weight to impact these weaknesses. So pay attention to the variability out there as it is a heads up day and remember a few key points. New loading has been occurring over the past 24 hours; natural avalanche activity has occurred during this same timeframe; hard slabs have formed over 6% snow that fell at the end of Wednesday’s storm; and it has remained cold over the past 72 hours allowing slabs to retain their elastic energy and propagation potential.
Now for the WINTER STORM WARNING that goes into effect tonight into Sunday morning. Talk about a flip flop storm track. Our mountains were expecting about 2” (5cm) until last night’s model run which showed a more inland track for the weathermaker. Expectations are up to a foot in the higher terrain of the Whites with snow anticipated to be wet and heavy due to a very thick layer of warm air. Light snow should begin moving in this afternoon, but should not affect avalanche danger much during daylight hours. As we move through the evening intensity will pick up and precipitation should be falling in earnest by midnight. Although this advisory expires at midnight today’s ratings do not reflect what might be developing between 9 and 11:59pm
- 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.
Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856