This information was published 02/10/2020 at 6:55 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Avalanche danger will increase throughout the day. Expect human triggered avalanches to become likely. Forecast snow totals vary, but if we see the upper end of accumulation, natural avalanches will become possible. Poor visibility from blowing snow will make terrain management difficult unless you have an intimate knowledge of your surroundings. Conservative decision making today is recommended. As the snow accumulates, we will see avalanche danger increase to CONSIDERABLE.
Yesterday, snow started falling mid-afternoon on a west wind. Continued light snow showers produced 1.1” of 4.5% snow on the summit (closer to 2” at Hermit Lake) while wind shifted between W and SW blowing 35-55mph.
Today, snow will continue to accumulate through the day. Moderate snowfall rates (1” per hour) are expected at times this morning tapering off this afternoon. MWObs is calling for 2-4” and NWS forecasts the higher side of that figure. Current SW wind in the 45-60mph range will soon shift to due W and increase to 50-70mph. While they valleys may see rain, temperatures in avalanche terrain should stay below freezing.
Tomorrow may bring another round of snow, with up to 2” possible. The greatest chance of visibility tomorrow will be early morning. Temperatures may rise above freezing below 3500’.
Primary Avalanche Problem – Wind Slab
Wind slabs are forming and will be reactive to human triggers. This type of avalanche problem is most unstable when forming and can often break above you. These will rest on a variety of bed surfaces, including wind slabs that formed Saturday and a melt/freeze crust from Friday. The depth of today’s wind slabs will depend on the amount of snow we actually get; four inches of snow on forecast wind could produce wind slabs over two feet thick quickly, enough to bury a person.
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.
Field observations Sunday in Tuckerman and Huntington revealed a widespread melt/freeze crust that formed on Friday. The crust was topped with wind slabs in specific locations, the lee of a W wind as well as some crossloaded aspects. These wind slabs were firm and stubborn, though upside down in structure. Snow arriving today will form reactive wind slabs on top of this. It’s possible that an avalanche could step down into wind slab that formed Saturday, but this stepping-down should not really factor into decision making as the real driver of instability today is the rapidly forming wind slabs.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch and will provide a good alternative for those who want to keep it conservative today.
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 02/10/2020 at 6:55 AM.
USDA Forest Service
White Mountain National Forest
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