Avalanche Forecast for Saturday, March 14, 2020
This information was published 03/14/2020 at 7:04 AM.
The Bottom Line
The snowpack in our forecast area was wetted at most elevations yesterday before refreezing under falling temperatures creating a sliding fall hazard in steep terrain. Watch for isolated pockets of wind slab in sheltered terrain that will be masking the icy surface below. Stiff boots, crampons, ice axe and the skills to use them are required basic tools to be safe today. Avalanche danger is LOW. Natural and human triggered avalanches are unlikely.
Yesterday, the summit of Mt Washington recorded a mix of precipitation types including snow, ice pellets, and freezing rain resulting in just 1.4” total snowfall from the 0.43” of liquid precipitation that fell. Hermit Lake recorded 2.3” of snow, noting precipitation went from snow to sleet to rain then back to snow/sleet with a 2cm ice crust. Temperatures peaked at 32F around 3pm on a 70-90 mph W wind, before falling sharply as wind shifted W at 70-100 mph through the night.
Today, west wind will shift NW and continue to rage at 70-90 with gusts up to 120 mph early, then ease off slightly through the day. Temperatures will remain in the upper single digits F with a chance of snow showers producing a trace to 1”.
Tomorrow, expect clearing skies with continued cold temperatures in the single digits above. North west wind at 50-60 mph. No snow is forecast.
Primary Avalanche Problem – Wind Slab
Small wind slabs formed from the 1.4” of new snow yesterday may be found in sheltered terrain and are likely unreactive. While this is a seemingly small avalanche problem, it can be a big hazard when barely covering a slick bed surface in steep terrain.
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.
Yesterday’s mixed precipitation at mid and upper elevations was unlikely to eliminate the frozen surface, sliding fall hazard since Tuesday’s warm rain and the subsequent re-freeze. It’s likely that patches of new snow can be found, and while in some places the snow may be thick enough to hold an edge, in others the snow will be thin and barely covering the icy surface. With strong wind trying to push you off your feet, and the fact that a stumble can result in a sliding fall, today is a good day to dial back expectations.
The Sherburne and Gulf of Slides ski trails remain 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 03/14/2020 at 7:04 AM.
USDA Forest Service
White Mountain National Forest