This information was published 02/09/2020 at 7:10 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
The avalanche danger is MODERATE today in areas of wind drifted snow. Human triggered avalanches are possible. The most likely places to trigger an avalanche today are on steep slopes and cross loaded gullies in eastern ravines above 3500’. While skies remain clear, these areas of concern will be easy to see as smooth pillows of snow and will be dull in appearance. Evaluate snow and terrain carefully, using safe travel practices by traveling one at a time. A sliding fall hazard may exist in areas of wind scoured, frozen snow. Likely areas for this include the tops of gullies in the eastern ravines or anywhere that wind has scoured snow from the ice crust. Protect yourself with crampons and ice axe in steep terrain.
Cold and strong wind yesterday. Strong 75+mph WNW wind affected the 7.5” of snow that fell Thursday and Friday. The day started at -9F on the summit and dropped to -17F in the afternoon. Blowing snow was reported by the OBS until 5pm, coinciding with the wind settling down.
Today, wind is from the WNW at 30 mph and will shift to the SW increasing to 45-60 mph. Temperatures will slowly warm to 10F. Clouds increase with a chance of afternoon snow showers: trace to 1”. Steady snow overnight may bring 1 to 3” on W wind blowing 50-70 mph.
Tomorrow snow continues with an additional 1 to 3” expected on SW & W wind at 50-70 mph. At this time, forecasts agree that temperatures will remain cold enough that all precip will fall as snow. Avalanche danger is likely to increase tonight and tomorrow with the new snow.
Primary Avalanche Problem – Wind Slab
Sustained strong winds have created stubborn hard slabs primarily in eastern ravines, but also any cross loaded gully in the range. These slabs will feel firm, but may still crack and fail under the weight of a skier/climber by finding a thin spot. Given the mixed precipitation during the recent storm, and wind patterns, there is a possibility these slabs rest on a weak interface or soft weak layer of snow.
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 20 hours of high winds, the recent wind slabs will be firm and very likely stubborn to a human trigger. The question remains: how well are these wind slabs bonded to the bed surface? Looking back at the hourly weather observations from the summit observatory, the light snow falling on 2/6 turned to ice pellets, then freezing drizzle, rain then back to freezing rain and heavy snow on 2/7. Looking at the hourly record from 2/7 at 3:47 pm during the period of heavy snow the wind was very light before ramping up, leading to the many hours of strong winds. From observations, we know a 1cm ice crust may be widespread. This suggests we may find a weak layer of soft snow beneath firm wind slabs. If you are out today, spend some time digging down with your hands or probing with your pole handle or ice axe. Let us know what you find with an observation.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. Beware of breakable crusts off trail.
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. Clickhere to check it out.
Recent snowpack and avalanche observations can be foundhere and on Instagram. Your observations help improve our forecast product. Please take a moment andsubmit 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 02/09/2020 at 7:10 AM.
USDA Forest Service
White Mountain National Forest
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