Avalanche Forecast for Sunday, January 5, 2020
This information was published 01/05/2020 at 7:00 AM.
The Bottom Line
The avalanche danger will be CONSIDERABLE today in terrain currently loading with wind driven snow. Natural avalanches are possible and human-triggered avalanches likely in steep, wind loaded terrain.
- Strong winds are building slabs which could be triggered by skier or climber.
- Wind slabs may be on the small side but could be large enough to carry a person and bury them in a terrain trap.
- These slabs are reloading an already icy bed surface across some areas such as Chute to Sluice in Tuckerman Ravine.
- The potential exists for an avalanche to trigger naturally due to continued wind loading or by a person from well below the starting zone.
The Lion Head Winter Route is open and remains the safer choice for accessing the summit of Mount Washington from the east. An ice axe and crampons are needed near treeline and above with micro-spikes useful in wind scoured areas.
The summit recorded about 3” of snow Saturday which fell on light winds through the day. Wind velocity increased rapidly around 4am this morning and will continue to blow from the northwest through the day in the 55-75 mph range with higher gusts. This is an ideal wind speed and direction for loading our prime avalanche terrain. Temperatures will remain in the teens on the summits today with the potential for another 2” of snow to fall.
Primary Avalanche Problem – Wind Slab
New wind slabs began to form early this morning and may be at peak instability and a dangerous size mid-day. Carefully evaluate the terrain and snow pack and give a wide berth to avalanche paths. Best to keep the angle low and avoid any overhead hazard if skiing. Continuous sluffing from steep pitches of ice and cliff bands will grow these wind slabs as well.
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.
It has been three days since any reported avalanche activity that followed the snow and wind loading event around the New Year. There have been many observations of clean shears in the moderate range at various depths in that snow though. New snow falling yesterday and today could lead to more avalanches despite the small amount of new snow fall. History has shown that a northwest wind can quickly turn small amounts of snow falling onto the plateau-like feature above the east facing ravines and gulfs into thick and dangerous slabs. The new snow which fell yesterday may have bonded to the various textures of existing snow surfaces but that is not relevant when considering a wind slab growing on top. That new snow is more likely to be the soft, weak layer that is unable to support the wind slab growing above.
Conditions on the Sherburne ski trail have improved with the recent snowfall though a few rocks and ice patches have emerged after heavy holiday traffic. A few partly open water bars remain.
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 01/05/2020 at 7:00 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest