This information was published 01/13/2020 at 7:06 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Refrozen, icy snow presents an equal or greater danger than the small drifted pockets of wind slab that may be found in the terrain today. Arresting a fall in steep terrain may not be possible. As you choose your terrain today, consider the consequences of a long sliding fall, which could be caused by a stumble, or even a very small avalanche. Crampons, an ice axe and well practiced skills to use them are essential tools for our current conditions. Warm rain events often add challenges to ice climbs, including undermined ice and ice dams with pressured water behind.
Temperatures have returned to seasonable teens F after this weekend’s warm rain. The half inch of new snow that fell at the tail end of this system yesterday was affected by W wind blowing for several hours at 70-80 MPH. Mostly cloudy skies are forecast today with temperatures in the 20s F and W wind will increase through the day to 45-60 mph. Up to 1” of snow is possible this afternoon. A continuous chance for light snow showers for the next 48 hours with more significant snow Tuesday night may bring increased avalanche danger by Wednesday.
Primary Avalanche Problem – Wind Slab
Wind slabs that are small in size may be reactive to a human trigger, but should be sufficiently isolated in distribution to be easily avoided. Any new snow today will fall on strong west wind adding to this avalanche problem. Keep in mind a small avalanche on a steep and frozen snow slope today can bring big consequences.
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.
Mount Washington Observatory recorded 1.38” of rain this weekend, with daily high temperatures of 42F on Saturday and 45F early Sunday. The ravines likely experienced 36 hours of above freezing temperatures. The Hermit Lake snow plot was 0 C at -20cm Sunday morning with 25cm settlement since Friday. This was a significant warming event and once this snowpack refreezes will be the new bed surface for future avalanche problems.
Visibility has been limited, though with the return of seasonably cold temperatures we can expect the snowpack is well on the way to a refrozen state of stability and the small wind slabs which may have formed overnight and later today are our only avalanche concern.
The Sherburne and Gulf of Slides ski trails are heavily damaged by rain and warm temps.
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 01/13/2020 at 7:06 AM.
USDA Forest Service
White Mountain National Forest
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