This advisory expires tonight at 12:00 midnight.
Tuckerman Ravine has Moderate and Low avalanche danger. The Sluice, Lip, Center Bowl, and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. All other forecast areas have Low avalanche danger. Natural and human-triggered avalanches are unlikely, although unstable snow in isolated terrain features may exist.
Huntington Ravine has Moderate and Low avalanche danger. North Gully, Damnation, Yale, Central, and Pinnacle have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Odell Gully, South, and Escape Hatch have Low avalanche danger. Natural and human-triggered avalanches are unlikely, although unstable snow in isolated terrain features may exist.
AVALANCHE PROBLEM: Persistent Slabs are the #1 avalanche problem today. Wind slabs laid into the Ravines at varying times over the past 10 days have all transitioned to being “Persistent”. These slabs are sitting on weak faceted crystals that are advanced in some areas depending on the specific layering unique to that location. We are not finding these weaknesses consistently across the terrain, but in varying degrees so expect a lot of spatial variability in how these facets effect the Persistent Slab issue. The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. The slabs can propagate in surprising ways making this problem more difficult to predict, assess and manage than wind or storm slabs requiring a wide safety buffer to handle the uncertainty.
WEATHER: A chance of snow showers today should remain light and not contribute to snow instability, but will hover over the mountain effecting visibility for a while. Temperatures will drop rapidly from positive territory deep into negative terrain through the day, perhaps hitting -30F tonight. This will be associated with a mean, ripping wind, gusting to 115mph (185kph) around midnight. By dusk today expect winds to be approaching the century mark. Saturday morning will start out rugged with full arctic conditions, but temper through the day due to dropping winds and rising mercury.
SNOWPACK: Moving around in the Fan of Huntington Ravine to the ice bulge in Central Gully yesterday was a good way to drive home the point that our snowpack is highly diverse from one point to another. Boot and ski penetration varied from place to place, but the opportunity to travel in boot height snow was plentiful. The ice crust vapor barrier that is contributing to the development of our faceted weak layer was found at varying depths and thicknesses. At times it was near the surface and highly fragile. We dug numerous hand pits in areas of softer snow in the Fan, beneath the Central bulge and along the way over towards Harvard Bulge. This route confirmed the presence of the weak layer of advanced 1-2mm facets. The good news is the slab on top is stubborn and not very reactive in most locations. The concern and uncertainty lie in those locations where the slab is under greater tension, i.e. really steep, convex or in locations where there are thin spots that would be more reactive to a human trigger. Stability tests that demonstrate “good stability” can trick people into thinking persistent slabs are fine, until someone hits one of these “sweet spots” due to the current spatial variability. Safe travel techniques are warranted, whether the rating is Low or Moderate, particularly when dealing with Persistent Slabs. Looking ahead, sustained cold could set us up for problems when this snowpack gets stressed with more snow or rapid warming.
The Sherburne ski trail is a nice alternative for people looking to ski without exposing themselves to this today’s high winds and cold. The summer Lionhead trail remains open. Look for our Weekend Update this afternoon.
- Safe travel in avalanche terrain requires training and experience. This advisory 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.
- Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast.
- For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin.
- Posted 7:45 a.m. January 16, 2015. A new advisory will be issued tomorrow.
Christopher Joosen/Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856