This information was published 01/11/2019 at 7:14 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Continued wind loading raises the threat of large natural avalanches in specific east facing areas of the range today. Avalanche danger is teetering between ratings with the potential large size of natural avalanches pushing the rating to CONSIDERABLE in a few areas with the largest wind slabs. Human triggered avalanches remain possible in MODERATE rated areas due to the potential for reactive but smaller wind slabs. Remember that active wind loading can be the heavy trigger needed for a large slab to fail but the weight of a passing skier or climber may also be enough. Cautious route finding will be required to evaluate snow and terrain today.
In the past 24 hours, 7.5” of new snow brought our three day total to 21” at higher elevations. Yesterday’s new snow was accompanied by strong winds averaging around 70 mph from the NW. New snow shut off shortly after dark last night but wind slowly increased through the night and is currently blowing in the 80-90 mph range. Wind seems likely to increase further with gusts over 100 mph. Skies may clear but count on blowing snow and passing fog and clouds to create challenging conditions for gathering visual observations. The current summit temperature is -9F and won’t warm much before falling further overnight.
Primary Avalanche Problem – Wind Slab
The strongest wind since Wednesday evening will add more snow load to existing wind slabs today. Confidence is high that these wind slabs will be firm and stubborn in most areas but continued snow loading keeps the threat of large natural avalanches real, particularly in specific areas like the Headwall of Tuckerman Ravine. Other east facing terrain with sufficient fetch downwind could also harbor these large but stubborn wind slabs.
What is a Windslab Avalanche?
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Three days of snow, wind loading and zero visibility have left us with little direct observation of our avalanche paths. A history of observations of our primary forecast terrain leads us to our current forecast. The strong wind on tap will scour and wind pack some zones while further loading sheltered areas. Continued sluffing will also build wind slabs beneath steep features like the approach to Pinnacle, the big ice slab in Odell and below chokepoints in the Chute. Both loading conditions will occur in the Headwall area of Tuckerman Ravine.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
Safe travel in avalanche terrain requires training and experience. This forecast 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.
Avalanche danger may change when actual weather differs from the higher summits forecast.
For more information contact the US Forest Service Snow Rangers, AMC visitor services staff at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or seasonally at the Harvard Cabin (generally December 1 through March 31). The Mount Washington Ski Patrol is also available on spring weekends.
Posted 01/11/2019 at 7:14 AM.
USDA Forest Service
White Mountain National Forest
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