Posted 8:30a.m., Friday, February 18th, 2011
Tuckerman Ravine has CONSIDERABLE avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. The only exception to this rating is the Little Headwall which has Low avalanche danger. Natural and human triggered avalanches are unlikely.
All forecast areas of Huntington Ravine have MODERATE avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.
The key factor for snow stability in the ravines today is free water in the snowpack. Temperatures in the ravines have been hovering in the 35-40F (2-5C) range for more than 24 hours now. This is causing the snowpack to melt away, and as this happens the water has to go someplace. Wet slabs can be fickle beasts, and knowing exactly how much water is needed to weaken a slab to the point of fracture and failure is more or less impossible. You’ve got to rely on the factors you can measure or observe, and make educated decisions from there. In this case, we know the temperatures in the ravines have been above freezing for a period of time, and we know that prior to the warm-up there were existing wind slabs with underlying layers that ranged from facets under eroding crusts to wind-hammered hard slabs. Today’s weather forecast leads me to believe temperatures will be warmer today than yesterday, and remain above freezing at the ravine elevations until sometime after dark. Free water will continue to percolate into the snowpack until we move below freezing later tonight. The combination of all these factors leads to the conclusion that natural avalanche activity is possible in Tuckerman Ravine. In Huntington Ravine, the weather factors will be the same as in Tuckerman, the difference between the two is predominantly related to the existence of slabs prior to the warm-up. Huntington had less new surface slabs and much more wind-hammered surfaces. The bump up to Moderate today reflects the continued application of heat to the snowpack and the increase in size and distribution of potential avalanches that goes along with it. In other words, although naturally triggered avalanches remain unlikely, you can expect avalanche danger to be relatively greater than what you’d find under a Low rating. Furthermore with Huntington, you’ll want to pay attention to the increased potential for falling rock and ice. Wet slabs being what they are, I would not recommend relying too heavily on snowpit stability test results as an indicator of stability today.
The upcoming weekend is a holiday weekend, and the following week is a school vacation week. These are two factors that typically combine to put lots of people out and about in the mountains. If you’re going to be one of them, be sure to check the latest weather forecasts before heading above treeline or the latest advisory before heading into avalanche terrain. Tonight I expect temperatures to drop well below freezing, which will turn much of the water-logged snowpack into something akin to polished concrete, particularly in steep terrain. In other terrain, such as down lower in the flats or in transitions from flat to steep, you might find nasty breakable crusts in one location and rock solid hardpack a few feet away. Winds tomorrow will be raging on the mountain, and a little bit of snow can be expected. If you’re thinking of doing a run on a backcountry ski trail, consider sharpening your edges or else bringing along a full set of hockey pads; it’ll be challenging conditions after it all freezes solid. All in all it’s going to be a tough day in the mountains tomorrow. We’ll get into more detail tonight in the Weekend Update section of our website.
- 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.
Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856