This information was published 01/05/2019 at 7:07 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Slopes holding large areas of wind drifted snow could produce an avalanche from a human trigger today. Warming may ultimately contribute to human triggered avalanches being likely in these recently formed wind slabs. The Headwall of Tuckerman Ravine holds the largest of these slabs and therefore has CONSIDERABLE avalanche danger. All other areas have MODERATEavalanche danger, with the Northern Gullies of Huntington Ravine as the one exception with LOW avalanche danger. Be mindful that the soft snow that you will likely be drawn to is today’s avalanche problem in most of our terrain.
Several hours of sustained 70 mph W wind yesterday morning has slowly decreased to the current 35 mph. Wind today will continue to diminish, ultimately to around 10 mph on the higher summits. Tonight wind will remain calm from the SW before shifting NW and ramping back up. Minimal precipitation occurred yesterday and none is expected today. Partly cloudy skies this morning should become increasingly cloudy through the day. It’s currently 25F on the summit and temperatures should push above freezing in all of our terrain. Tomorrow brings a chance at 1-3 inches of snow falling on our typical strong NW winds.
Primary Avalanche Problem – Wind Slab
Wind slab that formed since Thursday should remain reactive to a human trigger today. Warming today may increase the likelihood of a human triggered avalanche. Areas of this slab do vary significantly in size. Terrain with smaller and thinner pockets will present a more manageable avalanche problem than places where the slabs are large and possibly several feet thick. Realize that today’s danger ratings are based primarily on potential size of an avalanche, and that a small avalanche in the wrong place can be a big deal.
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 multiple recent melt freeze events have created robust crusts that keep our stability concerns focused on snow which has fallen and been wind transported since Monday night. Terrain with a significant upwind fetch area for wind loading, like Tuckerman Ravine, have large areas of new wind slab that may be quite thick. The wind slab formed since Thursday tends to be cohesive and often layered over less cohesive snow. This poor structure was touchy yesterday and is likely present in large and small slabs alike. Wind has also scoured to crust in many locations across many aspects, though the crust appears bright white and can be difficult to visually identify. A solid partner and dialed snowpack evaluation skills will be essential to managing the current avalanche problem and scoring good turns.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
Sustained above freezing temperatures at low elevations today may make icefall a concern, particularly in lower elevations.
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 01/05/2019 at 7:07 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
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