Avalanche Forecast for Friday, January 10, 2020
This information was published 01/10/2020 at 7:12 AM.
The Bottom Line
Wind driven snow that accumulated through the week remains a concern in steep terrain. Evaluate snow carefully and understand that these slabs may be firm underfoot but could crack and fail under your weight. Thin spots in the slab such as over a boulder or the ice bulge in the Main Gully in Gulf of Slides can be the weak spot where a crack develops. Move one at a time and avoid pillows of hollow snow when you can. Human triggered avalanches remain possible today giving us a MODERATE avalanche danger rating.
An approaching weather system will bring warming temperatures and frozen forms of precipitation turning to freezing rain and rain by day’s end. The temperature at 3-4,000 is already above freezing with much colder air pooling in the valleys below. Precipitation falling today should not affect snow stability but will certainly make skiing or hiking unpleasant. Wind will be from the west at 60-80 mph with summit temperature reaching 30 by the end of the day.
Primary Avalanche Problem – Wind Slab
Wind slabs exist in many areas after the wind loading that occurred through the week. These slabs have not settled and bonded yet. Most of these will appear hard and stubborn underfoot but they contain weak layers of softer snow and rest on an icy and flat (though coarse from riming) bed surface that has proven itself to be a contributor to what is a lingering avalanche problem. Look for and avoid wind driven snow piled up at the base of steep areas such as low in Chute and Right Gully as well as in sheltered locations like Odell Gully and mid-slope in the south snowfields of Gulf of Slides.
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.
Field reports are limited but good visibility allowed some observations yesterday in a few areas. The most recent avalanche cycle is a good reminder that small amounts of snow can build large slabs and can produce natural avalanches. The large avalanche in Tuckerman Ravine is dramatic and it’s location high across the Headwall and into the upper Lip is not typical and likely a result of the low wind speeds that allowed snow falling earlier in the week to accumulate higher in the terrain than it usually does. Two other field reports indicate avalanches occurred low in the exit from Diagonal, above the Harvard ice bulge and also a report from outside our forecast area on North Baldface.
There is no hard evidence as to where exactly the college group triggered the avalanche in Tuckerman Ravine for those of you wondering. Suffice it to say that crown lines weren’t visible in the locations that could have produced an avalanche with no injuries from the Lip or Sluice. Perhaps things reloading and an exceptional degree of luck played a role or perhaps the group wasn’t where they thought they were. In any case, inexperience and unfamiliarity with the terrain combined to create a significant close call that could have ended tragically. Please do your homework, navigate carefully or hire an experienced guide. Mount Washington may be short but it is fierce.
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 01/10/2020 at 7:12 AM.
USDA Forest Service
White Mountain National Forest