Avalanche Forecast for Tuesday, January 14, 2020
This information was published 01/14/2020 at 7:01 AM.
The Bottom Line
Warm rain this past weekend followed by two days of cold temperatures created a hard slick crust as our primary snow surface. While you may be able to find isolated and small pockets of wind slab from the .8” of new snow yesterday, long sliding falls on the refrozen snow surface are the greater concern. The avalanche danger is LOW today.
The term Long Sliding Falls is mentioned in this forecast from time to time when a wet snow surface refreezes. The significance and danger of a small stumble on seemingly benign terrain cannot be overstated. If you have not practiced self arrest with an ice axe you should. If you have practiced, know that the effectiveness of this skill is limited in the hard icy snow you’ll encounter in the mountains today. Self arrest is a last resort and may only serve to slow you down on your way to the floor of the ravine. In these conditions, very careful movement is necessary to prevent a fall from happening in the first place. Put crampons on before slopes steepen and get your ice axe out and ready before you expect to need it.
Just under an inch of snow was recorded on the summit yesterday afternoon on a WSW wind and 1cm at the Harvard Cabin snow plot. Today we’ll see temperatures in the upper teens F under cloudy skies with SW winds at 15 to 30 mph. Lingering moisture may result in afternoon snow showers: trace to less than an inch. Overnight, 1 to 3 inches of snow are possible as 30-35 mph SW wind shifts to the NW increasing to 50-70 mph. An additional inch of snow possible Wednesday morning, then 2 to 4 inches Wednesday night into Thursday.
Primary Avalanche Problem – Wind Slab
You may be able to find small isolated pockets of wind slab today but should be sufficiently isolated in distribution to be easily avoided. If you are brave enough to be on skis today, you may be drawn to these smooth fresh snow wind slabs; keep in mind a small seemingly inconsequential pocket of new snow may trip you up and result in a high consequence sliding fall.
Looking forward, new snow tonight and the next few days will be affected by NW wind, likely resulting in increasing avalanche danger. Watch for small, isolated pockets of wind slabs becoming larger, thicker, more widespread and a more significant avalanche problem than we have today.
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 recently wetted snowpack is refrozen. The crust on the surface is likely to be strong and supportive in steep, open terrain, though may remain breakable in the trees and at lower elevations. This rain freeze crust will be a factor in future snow pack stability. Avalanche paths in eastern ravines are well developed and now have a widespread smooth bed surface for future avalanches.
The Sherburne ski trail is a refrozen mess, though still mostly snow covered. Expect hard snow, water ice, rocks and even frozen mud.
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 01/14/2020 at 7:01 AM.
USDA Forest Service
White Mountain National Forest