Avalanche Forecast for Tuesday, February 11, 2020
This information was published 02/11/2020 at 7:08 AM.
The Bottom Line
Human triggered avalanches remain likely today in areas of wind drifted snow. The most likely places to trigger an avalanche today are on steep slopes and cross loaded gullies. Evaluate the snowpack carefully as you move through the terrain. Watch for signs of recent wind loading: smooth snow surface, pillows of new snow and deep sluff-pile aprons of snow at the bottom of steep gullies. Avalanche danger is CONSIDERABLE.
Yesterday, overnight light snow that began Sunday evening continued into the early afternoon for a storm total of 5.2” on the summit. Hermit Lake Snow Plot recorded 3.5” of 14% snow. During the hours of snowfall, a 50-60 mph SW wind transitioned to the W mid-morning and remained, finally transitioning NW in the early evening. Temperatures warmed to the teens F.
Today, temperatures will rise to the lower 20sF. SW wind at 20-35 mph will slowly shift W and increase to 45-60 mph. A trace to 2” of new snow is possible this afternoon & overnight. Tonight wind from the NW will increase to 65-85 with gusts reaching 100 mph.
Tomorrow, NW wind 65-85 will shift W and decrease to 45-60 mph. Trace to 1” new snow possible as morning snow showers.
Primary Avalanche Problem – Wind Slab
Recent snow and wind has formed slabs that are likely sensitive to human triggers, and deep enough to bury a person. Instabilities are most likely to be found in steep slopes and cross loaded gullies above 3500’. Pay attention to surface textures and how “slabby” the snow feels and watch for shooting cracks underfoot as a red flag for sensitivity.
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.
Of the many factors used to determine the danger rating today, sensitivity to a human trigger was a sticking point in the discussion this morning. Looking back at the hourly records from the MWObs, we can see that the new snow was affected by 50-60 mph wind during almost the entire storm. Wind speeds directly influence the sensitivity of a wind slab. Light winds will create a softer, more sensitive wind slab while strong winds will pack the snow particles down forming a less sensitive wind slab. Based on recorded wind speeds alone, we were leaning towards the slabs being more stubborn than reactive, however due to the recency of these new slabs, and observations late afternoon and this morning we concluded there’s still a good chance that the slabs could be reactive to a human trigger. As always, please let us know what you find today by posting an observation.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
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 02/11/2020 at 7:08 AM.
USDA Forest Service
White Mountain National Forest