This information was published 02/03/2020 at 7:19 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Human triggered avalanches are possible today where wind will combine with new snow, and possibly existing snow above treeline, to form new wind slabs. You are most likely to encounter this avalanche problem on steep slopes and cross loaded gullies in eastern ravines above 3500’ elevations. Evaluate snow carefully as you move through the terrain. Blowing snow will make identifying new wind slabs challenging from a distance. Today’s hazard rating is MODERATE.
Yesterday, 0.2” of snow was recorded on the summit of Mt. Washington with a trace recorded at Hermit Lake. North west wind remained fairly steady during daylight hours at 15-20 mph. Temperatures hovered around 10 F.
Today, 1 – 3” of snow is forecast. Higher intensity snow showers are more likely in the afternoon hours. West wind at 60-80mph and temperatures in the lower teens F. Chance for a trace to 1” of snow overnight.
Tomorrow, in the clouds with snow showers accumulating to 1-2”. Temperatures in the lower 20sF and west wind 35-50mph.
Primary Avalanche Problem – Wind Slab
Several inches of snow above 5500’ is likely available for transport by the increased wind today, and up to 3” of new snow will provide enough raw materials to build wind slabs. These new wind slabs forming today may be reactive, especially in locations that avoid the strongest wind. Melt freeze crusts on the snow surface may exacerbate this problem by providing a icy bed surface.
The existing snowpack structure leading into today remains a concern, though less so as more observations come in suggesting settlement and unreactivity. The possibility exists for an avalanche today to trigger deeper into the existing snowpack.
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.
Today’s avalanche problem is largely driven by the new snow expected today and any remaining snow above treeline available for transport into the ravines. Both factors include a level of uncertainty: new snow from snow showers can result in much less than predicted, and also significantly more than predicted. The OBS hints at the possibility of exceeding expected snow totals today, while the NWS is predicting less than 2” and much of that later this afternoon. Information from hikers, and relatively slow wind speeds recently leads us to believe that there may be several inches of snow available for transport, though ice crusts may or may not keep that snow locked to the ground.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch with good skiing most of the way down. Beware of breakable crusts off trail.
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 02/03/2020 at 7:19 AM.
USDA Forest Service
White Mountain National Forest
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