Avalanche Forecast for Thursday, December 27, 2018
This information was published 12/27/2018 at 7:03 AM.
The Bottom Line
Lingering pockets of wind slab exist scattered across the hard, refrozen surface snow in our steep terrain. The hard surface will require crampons, an ice axe and good climbing technique to avoid a slip which could quickly turn into a long, sliding fall. Ice climbs were damaged by the recent rain so be on the lookout for pressure building behind ice with the potential for rupturing.
2cm of new snow fell at Hermit Lake with half an inch recorded on the summit of Mt. Washington during snow shower activity in the past 24 hours. Around 4.5” of snow has fallen on the summit in the past five days. Current temperature on the summit is -2F with wind from the NW at 56mph. Temperatures will warm to the teens on the summits through the day as wind subsides and shifts west at 30-45 mph, and even lower in the afternoon. The next round of precipitation arrives tonight and continues through tomorrow with 4-6” of snow falling overnight on increasing south west winds before a transition to sleet, freezing rain and finally rain by afternoon all the way to the higher summits.
Primary Avalanche Problem – Wind Slab
Wind slabs built over the past few days are likely to be stubborn but assess them before committing to steep slopes with newer snow. Even a small avalanche can have significant consequences in steep terrain, particularly with our currently icy surface conditions.
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.
There has been no reported avalanche activity since the 3” of rain fell December 21-22 and “reset” our snowpack. New snow and mixed precipitation coming tonight and tomorrow will be arriving with building winds and increasingly dense snow before changing over to sleet and rain. The window of enough snow to slide on without avalanches due to building wind slab or wet slab danger seems tiny if it exists at all.
The Sherburne and Gulf of Slides ski trails have snow and ice coverage to Pinkham Notch. Heavy rain on December 21-22 did some damage and melted snow in some waterbars.
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 12/27/2018 at 7:03 AM.
USDA Forest Service
White Mountain National Forest