Avalanche Forecast for Wednesday, March 11, 2020
This information was published 03/11/2020 at 7:13 AM.
The Bottom Line
The snowpack in our forecast area refroze overnight leaving a sliding fall hazard in steep terrain. The half inch of snow that fell last night is unlikely to do much more than obscure the frozen surface. In wind sheltered terrain, the new snow may have accumulated into small pockets of wind slab which will contribute to what is largely a long sliding fall hazard kind of day. With the summit temperature remaining in the mid-teens through today, the freeze line is likely to remain below ravine elevations despite some sunshine in the forecast mid-day. Crampons, an ice axe and a strong conviction to avoid a slip and fall will be more than useful if you choose to poke into mid and upper elevation terrain. Avalanche danger is LOW today with natural and human-triggered avalanches unlikely.
Yesterday, temperatures at ravine elevations remained above freezing for a total of 36 hours of melting and settlement. In the past 12 hours or so, .45” of rain fell followed by 0.5” of snow.
Today, temperatures are much cooler with freezing temperatures from Pinkham Notch to the summit where the current temperature is 10F. Hermit Lake and Gray Knob each reported a trace of snow with current snow temperatures of -7C 20cm down from the surface at Gray Knob and -1C at Hermit Lake. Summit temperature today will remain in the mid-teens F with winds diminishing to the mid-30mph range under partly sunny skies. Clouds will begin building again mid-afternoon.
Tomorrow brings clear skies in the morning with temps in the teens F and building cloud cover in the afternoon that could bring another inch of snow. Wind will be from the west 20-35mph.
Primary Avalanche Problem – Wind Slab
A small amount of new snow last night may have formed thin wind slabs in sheltered, east facing terrain creating a mosaic of softer new snow and icy refrozen crust. Any wind slabs will be small and probably fairly well bonded but will do little to improve skiing conditions in steep terrain where the new snow will be easily scraped off.
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.
This is the time of year when our snowpack becomes more unpredictable. As any veteran backcountry skier can tell you, a difference of a few degrees Fahrenheit can make a world of difference in skiing quality and level of hazard. We made it through the first warming in a while yesterday with no avalanches reported though snow was reported to be sloppy in some areas and some minor wet loose activity. This is a good clue that frozen chunky snow, a.k.a. death cookies, are also on tap today. Though valley temps may become spring-like this afternoon, an analysis of modeled cloud cover and timing makes it doubtful that temps will rise enough to create enjoyable skiing at ravine elevations. Cramponing and climbing conditions will likely be fine, though plan to rope up early since very firm conditions will exist in steep, mid and upper elevations such as Huntington Ravine.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
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. Click here to check it out.
Recent snowpack and avalanche observations can be found here and on Instagram. Your observations help improve our forecast product. Please take a moment and submit 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 03/11/2020 at 7:13 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest