Avalanche Forecast for Wednesday, January 29, 2020
This information was published 01/29/2020 at 7:06 AM.
The Bottom Line
New snow in the past three days has created wind slabs that may be reactive to a human trigger. Evaluate the snow carefully as you choose your line and recognize that while these wind slabs may be stubborn and firm in places, they sit on a freezing rain crust, and are closer to reactive than stubborn in sheltered locations. Unsupported slopes or rollovers in gullies and steep areas below frozen waterfalls or cliffs in mostly east facing terrain are at the top of the list of concerns for triggering. Be watchful for signs of wind transported snow today as wind speeds increase. If snow begins to load slopes this afternoon, the danger rating will increase beyond the current MODERATE rating.
The wind shifted to the north this morning and will increase in speed today, possibly during daylight hours. This shift will move any snow remaining in alpine fetch areas. This is most likely to occur as the wind increases to the 40 mph range. Any remaining snow that is available for transport will likely blow into the terrain overnight as wind increases further into the 60’s mph. Temperatures will be seasonably cold today, around 10F on the summits, under clear skies. Generally a nice, cold day with good visibility.
Primary Avalanche Problem – Wind Slab
Be wary of the largest slopes with an eastern aspect. Wind slabs will be largest there and sit on an icy crust that developed Saturday. Natural avalanche activity yesterday morning on the slope below Duchess is a reminder that this snow can slide. Use the terrain to your advantage and consider staying on the ice crust if you are climbing as the crust is likely to reduce fracture potential. Keep a close eye on the ridge tops for wind blown plumes and on the ground for cascading sluffs of snow. Both are signs of increasing avalanche danger.
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.
The cycle of melt freeze crusts and new wind slabs continues to make our forecast a broken record, replaying the tired, old chorus over and over on a weekly, if not daily, basis. The ice crusts and wind slabs do not play well together and continue to create a lingering hazard that resists neat categorization into the avalanche problem continuum. These wind slabs have lingered frequently over the past 6 weeks or so and left folks wondering if they will ever be considered persistent slabs. This semantical difference is just that, a question of semantics. Since these wind slabs are generally easily identifiable in the terrain if you know what you are looking for, it would be misleading to call them persistent slabs since the avalanche problem is localized and remains consistent with the travel advice most useful when dealing with wind slabs. They aren’t time bombs resting on thick layers of persistent faceted grains, they are just the same old wind slabs that stubbornly resist change. Like any good, stubborn old New Englander, they won’t do what we want them to do, but at least they are consistently stubborn. Clear, cold nights with their hallmark, radiational cooling seem likely for the next couple nights so be prepared for more of the same stubborn old wind slabs hanging around in steep terrain.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. A generally warm winter has left open water in many areas, including water bars and often skiable drainages.
Details on daily snowfall totals, precipitation type, total depth of snow and other information can be found on our page devoted to snow study plot data. Click here to check it out.
Recent snowpack and avalanche observations can be found here and on Instagram. Your observations help improve our forecast product. Please take a moment and submit a photo or two and a brief description of snow and avalanche information that you gather in the field.
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 01/29/2020 at 7:06 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest