Avalanche Forecast for Thursday, January 17, 2019
This information was published 01/17/2019 at 7:03 AM.
The Bottom Line
Wind slabs in steep terrain should remain on your radar today. Older, stubborn and large slabs plus newer but smaller wind slabs are the main avalanche concern and earn a LOW danger rating. Both wind slabs are stubborn to a human trigger, but some exceptions may exist in the form of softer pockets. All of these slabs are resting on a smooth ice crust on which the last avalanche cycle occurred. If you brave the frigid and windy weather, bring your avalanche rescue gear along with crampons and an ice axe.
An arctic clipper brought an inch and a half of snow to higher terrain yesterday, with west wind averaging 60 mph and gusting to 108 mph. The temperature dropped 25 degrees in the past 24 hours to a brisk -17F. The mercury will rise to, but fall short of, the 0F mark with wind remaining in the 55-70 mph range under clear skies through the daylight hours. No snow is forecast today, though more snow may fall late tonight with more tomorrow which may bring 1-3” total.
Primary Avalanche Problem – Wind Slab
Wind slab that formed on January 10th and 11th remain a concern, primarily due to the icy bed surface that they are resting on. Though it would be unlikely for a person to trigger one of these slabs, the resulting avalanche could be large. Isolated pockets of wind slab formed yesterday due to new snow and a strong west wind. Areas in the Gulf of Slides and the Headwall of Tuckerman Ravine are most likely to contain the greatest concentration of this wind slab. These will be mostly firm and stubborn to trigger.
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.
Cold, clear conditions and a strong ice crust from Dec 23rd should keep you thinking about low probability and high consequence hard slab avalanches if you brave the cold weather and head into steep, high elevation terrain today. Triggering any type of firm slab that we grow so readily here usually takes some bad luck to find the thin spot in the slab. Stability tests of this type of avalanche problem generally show moderate strength weak layers but little propagation potential. Continue to dig but remember to limit your exposure to the risk by managing your terrain, moving one at a time and carrying your avalanche rescue gear. As we move forward in the season, realize that all our main avalanche paths are now fully developed with around 5’ of snow on the ground and multiple avalanche cycles filling in our paths.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
Come to a free avalanche awareness presentation at the LL Bean store in Freeport tonight, 7-8:30pm. Frank will be presenting a Know Before You Go program followed by information on the new forecast area with time for a Q&A session.
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 01/17/2019 at 7:03 AM.
USDA Forest Service
White Mountain National Forest