Avalanche Forecast for Saturday, February 1, 2020
This information was published 02/01/2020 at 7:10 AM.
The Bottom Line
Wind blown snow drifted down the steepest slopes and gullies and built wind slabs this week. You can avoid this potentially unstable snow by staying on the January 26 freezing rain crust that glazes much of the terrain. While no avalanches have been reported this week, the upside down nature of the snow and the large size of some of these isolated slabs leads us to a MODERATE danger rating again today. Evaluate the snow and consider your terrain before committing to skiing this snow. Large areas of accumulated snow, like below the cliffs of the Headwall of Tuckerman Ravine, have the largest slabs and greatest consequences. Areas scoured to the freezing rain crust have LOW avalanche hazard but create a long sliding fall concern. While generally breakable, this crust is very slick.
Ice climbing venues are going to be busy today. Lots of injuries have occurred due to icefall caused by climbers above other parties. Consider the value of choosing another route if folks are above you.
Mild, stable weather continues today with summit temperatures in the high teens. Cloud cover will persist, with summits likely shrouded in fog throughout the day. Flat light may make route-finding a bit challenging since it will be hard to tell the difference between the ice crust and newer wind packed snow surfaces. Wind from the west will diminish from 25-50 to 15-30 mph. Wind transported snow is unlikely today.
Primary Avalanche Problem – Wind Slab
Field work and observations indicate that the layers of ice and melt freeze crusts reduces propagation potential in the thickest slabs. Thin and mostly harmless surface slabs are more reactive on shady aspects. The snow structure leads us to believe a very large trigger would be required to trigger a deep slab on the January 13 ice crust a meter or more down. Sunshine and low winds have helped settle many south facing slopes.
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.
The complexity of the snowpack makes recreation challenging today. The softest snow for skiing is riddled with wind pressed surface snow that grabs your boots. The freezing rain crust that supports a skiers weight creates a tilted ice rink experience while skinning in scoured areas….leave your wide skis at home. Climbers will find the northern gullies in Huntington Ravine largely scoured while more wind sheltered climbs contain firm, stubborn wind slabs that may rest on a much softer layer of rimed snow. Though none of the slabs appear to be able to carry a crack any distance, it is worth considering the terrain configuration that they rest on. Dig frequently and avoid slabs in very steep or unsupported areas.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch with good skiing to about 2500’ where there is less snow and more ice. 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. 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 02/01/2020 at 7:10 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest