This information was published 02/14/2020 at 7:08 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
While triggering a small avalanche is possible in areas of sheltered, pillowed snow, it is the outside chance of a larger avalanche breaking wider and bigger than expected that is of main concern. Today is a good day to ease into terrain, evaluating the snowpack as you move through it. It is possible that a small avalanche could provide the mass needed to trigger a deeper weak layer. While unlikely, thin spots exist on large slopes that could act as trigger points for a larger avalanche. Identify these features of concern and manage them to your group’s ability. The avalanche danger today on slopes that contain wind drifted snow is MODERATE.
Yesterday, intermittent snow showers throughout the day delivered 2.1” of snow to the summit. West wind hovered around 35mph until mid-afternoon when speed increased overnight.
Today will be cold and grow colder, reaching -15F, with clearing skies. Early AM snow showers should abate with little accumulation. Wind is from the NW, blowing 70mph, and should decrease to 35-50mph later.
Tomorrow will be clear with highs on the summits around 10F. Wind from the west will start around 40mph and increase toward 80mph in the afternoon.
Primary Avalanche Problem – Wind Slab
Wind slabs exist in much of the terrain that is in the lee of a west wind and have been growing in size over the past 7 days. Wind speeds have remained below the scouring threshold, leaving a mix of firm, stubborn slabs in locations exposed to the wind while sheltered locations will have softer slabs that appeal to skiers. Changes in ski or boot penetration is a cause for concern and should indicate time to evaluate the snowpack, particularly when approaching steeper terrain, a convex feature, or a change in slope aspect.
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.
A week ago today was the most recent rain event that left a widespread breakable crust. Since that crust formed, 15” of snow has fallen on terrain above 3500’. This snow has fallen gradually with 1-4” each day on moderate wind from the western half of the compass. Looking above this crust, here are some observations that give us a degree of uncertainty today:
After an avalanche cycle occurred Monday, we have not observed or had any avalanche activity reported.
The structure of the snow has an inverted nature.
Digging in the snow will reveal many layers and clean interfaces.
Sheltered areas with softer snow contain enough energy to produce propagation.
The above points indicate bridging strength is winning over concerns of instability, but this could change due to the human factor running around the mountain. Good visibility today should aid in route-planning and help ensure you avoid traveling underneath another party.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch and offer great skiing and riding.
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 02/14/2020 at 7:08 AM.
USDA Forest Service
White Mountain National Forest
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