This information was published 12/24/2018 at 6:52 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Pockets of small wind slab that a human could trigger can be avoided by travelling on our widespread refrozen snow surface. All forecast areas have LOW avalanche danger. The hard, slick, refrozen snow present in our steep terrain makes long sliding falls a significant hazard today. Crampons, an ice axe, and your ability to use them effectively to avoid a fall are crucial for safe travel in the alpine. On our ice climbs, continue to be mindful of possible ice dams, or flowing water building pressure beneath recently frozen ice that could break with the placement of a tool or crampon.
Clear skies and temperatures in the teens F yesterday have given way to a weak low pressure system that is bringing cloud cover to the Presidential range. Clouds should persist all day, though we may see a few breaks this afternoon. Minimal to no precipitation is forecast as temperatures remain within a few degrees of the current 11F on the summit. Current summit wind is 25 mph from the W and may increase slightly while holding this general direction. For those planning to get into our mountains on Christmas, expect similar temperatures and slightly stronger wind than today under clear skies.
Primary Avalanche Problem – Wind Slab
Isolated wind slabs exist in the terrain and can generally be found on the eastern half of the compass rose. Formed Saturday night and into Sunday morning, these new pockets should range from stubborn to reactive to a human trigger. Plenty of opportunities exist to avoid these isolated slabs on our larger slopes, but it’s possible that our narrowest gullies could hold sections of wall to wall wind slab.
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.
The 3” of rain and sustained above freezing temperatures last week were followed by the current cold temperatures that have solidly refrozen our snowpack. The Lip in Tuckerman Ravine produced a large wet slab avalanche sometime during the rain storm, possibly late Friday or early Saturday. Our refrozen hard snow surface is actually quite smooth in many areas. The minimal new snow Saturday had enough ability to stick to the older snow to make most of our snow surfaces bright white in appearance, but recently formed wind slabs are the exception rather than the rule.
The Sherburne and Gulf of Slides ski trails are mostly snow covered to Pinkham Notch, but expect melted out areas to provide challenging conditions.
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 12/24/2018 at 6:52 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
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