This information was published 01/06/2020 at 7:43 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Human triggered avalanches are possible where the wind has drifted recent snowfall. Any new snow later this afternoon will be blown by the wind to form new slabs of drifted snow. Cliffs, trees, and terrain traps can increase the consequence of being caught in a slide. Picture where an avalanche would carry you before skiing or climbing steeper slopes. The avalanche danger is MODERATE today.
The 2.6” of snow Saturday and the 2.2” of snow Sunday was transported, drifted, packed and scoured (depending on where you look) by WNW wind in the 60-70 mph range on Sunday. Today, we start the day with a rare zen-like calm and clarity with a summit temperature of 7F and SSW at 6mph. Clear skies won’t last long, clouds and the chance for snow showers return early this afternoon. Wind will shift west and increase through the day to 45-60 mph. Up to 1” of new snow is possible by the end of the day. Tonight 1 to 2 more inches of snow are possible on continued W wind of 50-70mph. Tomorrow is forecast to be clearing with decreasing wind.
Primary Avalanche Problem – Wind Slab
New wind slabs formed from yesterday’s strong wind will generally be stiff with good bridging strength especially where most exposed to the strongest winds. However, even a stiff wind slab can be triggered to slide if you find a weak point in the form of a convex terrain feature, or a thin spot over buried rocks or bushes. Be alert to the consequences of triggering an avalanche and evaluate the terrain as you move about the mountains today. Watch for additional snow this afternoon and tonight drifting into new and possibly more sensitive 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.
It has been 4 days since the last known avalanche activity (link 1, link 2) and we expect the snow from the New Year’s Eve storm to be largely settled and likely unreactive. As predicting the stabilization of wind slabs includes a fair bit of uncertainty, and the fact that it’s been just 4 days, it would be wise to respect these older but larger wind slabs. With yesterday’s strong wind, new slabs will be mixed in with scoured terrain and feel stiff and supportive, while still susceptible to a human trigger.
The Lion Head Winter Route is open and remains the safer choice for accessing the summit of Mount Washington from the east. An ice axe and crampons are needed near treeline and above with micro-spikes useful in wind scoured areas.
Conditions on the Sherburne ski trail have improved with the recent snowfall though a few rocks and ice patches have emerged.
Details on daily snowfall totals, precipitation type, total depth of snow and other information can be found on our page devoted to snow study plot data. Clickhere to check it out.
Recent snowpack and avalanche observations can be foundhere and on Instagram. Your observations help improve our forecast product. Please take a moment andsubmit a photo or two and a brief description of snow and avalanche information that you gather in the field.
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 01/06/2020 at 7:43 AM.
Jeff Fongemie, Snow Ranger
USDA Forest Service
White Mountain National Forest
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