Avalanche Forecast for Tuesday, December 4, 2018
This information was published 12/04/2018 at 6:34 AM.
The Bottom Line
Areas of newly formed and relatively small wind slab are today’s avalanche problem, but long sliding falls on hard refrozen snow may be of greater concern to travelers in the alpine today. Watch for unstable snow on isolated terrain features. If you’re on soft snow in steep terrain, you’ll almost certainly be on the avalanche problem. Be sure you have an ice axe, crampons, and a strong skill set using them if you plan to travel on snow slopes today. Similarly, realize that even a small avalanche can easily cause a fall with potentially high consequences. All forecast areas have LOW avalanche danger today, due to the generally small size of new wind slabs.
Snow showers, sustained 60-80 mph NW and W winds, and dropping temperatures made yesterday a stark change from the previous warm and wet period. Snow totals ranged from 3.3 inches recorded on the summit to just over an inch at Hermit Lake. NW wind should continue and remain in the 50-70 mph range for the higher summits today. Temperatures are forecast to be steady through today and tonight at right around 0F on the summits. Cloud cover should decrease through the day, and we don’t expect any measurable precipitation. Tomorrow is forecast to be around 10 degrees warmer, with lighter wind and clearer skies.
Primary Avalanche Problem – Wind Slab
Areas of wind slab from snow which has fallen in the past 24 hours continue to develop on strong wind blowing from the NW today. These wind slabs will likely be small but reactive to a human trigger. With good visibility, avoiding these areas of soft, white new snow should be possible against the backdrop of hard, grey, refrozen snow in all but the most constricted terrain.
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.
Our upper snowpack has solidly refrozen following the warmup and rain of Sunday and Monday. Stability concerns are limited to the snow which fell yesterday and has been affected by predominantly NW wind, with several hours of W wind also recorded. This wind, which continues this morning, was strong enough to scour much of our terrain of new snow, leaving pockets of fresh wind slab that may be sensitive to a human trigger. Provided good visibility, it should be possible to travel on the refrozen old snow and generally avoid the avalanche problem today. Skiers and snowboarders seeking good turns will likely be drawn to the avalanche problem. Today is a great day to consider the consequences of an avalanche or fall in any terrain you consider travelling in.
Long sliding falls on the refrozen old snow surface may be of greater concern than avalanches in many areas of our terrain. Crampons, ice axe, and your knowledge of how to use them on steep hard snow will be essential for travel in the alpine today.
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 12/04/2018 at 6:34 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest