Avalanche Forecast for Wednesday, December 26, 2018
This information was published 12/26/2018 at 6:57 AM.
The Bottom Line
Isolated wind slabs exist on the steepest wind-sheltered areas on aspects facing away from a northwest wind. These smooth, pillowy looking areas are small and most likely stubborn to a human-trigger but are not entirely harmless due to the icy old snow that they are resting on. Fresh wind slabs may develop quickly this afternoon as wind speeds and the rate of snowfall increases. The hard and fast surface of rain-soaked and refrozen wind slabs in steep terrain create a risk as great as the wind slab avalanches. Crampons and an ice axe will be key safety tools for those braving the frigid temperatures and high winds today.
No new snow fell in the mountains during the past 24 hours. We are starting the day at -6F with 55 mph NW winds, clear skies and good visibility. Cold conditions will continue today, with strong NW winds on the increase. Windspeeds will ultimately reach the 60-80 mph range later this afternoon as clouds thicken and lower. Another inch or two of snow is possible as upslope snow showers begin later today. Light, dry snow and high winds will create a recipe for wind transported snow and more wind slab development. Tomorrow will be slightly warmer, with diminishing winds and clear skies. The next chance for precipitation comes Thursday night and Friday which should start as snow but end with rain.
Primary Avalanche Problem – Wind Slab
Assess the isolated pockets of wind slab on the steepest areas of wind sheltered slopes before you commit to walking or climbing on them. These smooth, pillowy looking areas are likely to be small but not entirely harmless due to the icy old snow that they are resting on. Wind slabs developing later this afternoon are likely to be more sensitive to triggering. Keep an eye on the rate of snowfall and snow blowing on the wind.
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.
After an exceptionally snowy November, December seems particularly….un-snowy. Just 23.3” of snow has fallen this month, though if the 3” of rain had fallen as snow that total snowfall would be more than double, bringing us back in line with the 45.5” average for the month. That rain event undermined snow and ice, opened up streams and generally caused mayhem in the steep terrain. The now icy surface has set us up for some challenging times for skiers, and created either good cramponing or long sliding fall conditions, depending on whether you are a glass half-full or half-empty kind of person. With any luck, this next storm on Thursday will spare us much rain or at least deliver a snowy refresh before switching over.
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 12/26/2018 at 6:57 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest