This information was published 02/02/2020 at 7:11 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Areas of drifted snow with an upside down structure can be found that could produce an avalanche today and exist mostly beneath the steepest slopes and cliffs. These places will likely draw skiers due to the better skiing quality. Remember that even a small avalanche in extreme terrain can have serious consequences. A busy weekend = watch for other parties traveling above you.
Today’s avalanche danger is MODERATE due to the unlikely chance a deeper instability is triggered, producing an avalanche capable of real harm. This is not a widespread issue and can easily be avoided by choosing terrain that is comfortable for your group and evaluating the snow. The largest areas of snow, east facing ravines, are where you will find this issue. Areas that are scoured to a crust have LOW danger today.
Yesterday, intermittent snowfall delivered 0.5” to the summit of Washington with a trace of accumulation below at 4000’. West wind calmed through the day with temperatures in the high teens to 20sF.
Today, lingering low level moisture will keep fog above 5500’ as well as the possibility of occasional snow showers, though expect similar totals to yesterday’s snow. West wind will increase to 35mph with temperatures staying below freezing at all elevations.
Looking ahead, we may see upslope snow showers dust our mid and high elevations tonight and tomorrow. Expect up to an inch by Monday night. Wind will begin a slow increase tonight from the west, blowing steadily around 60mph Monday morning where it should remain for the day.
Primary Avalanche Problem – Wind Slab
Our post-January 13 snowpack contains ice crusts that are resisting propagation. Currently these icy layers are found mixed with wind slabs sitting over a weak layer. Thin, soft wind slabs that formed over the past week can be found that may be possible to trigger, but the overall size of these will be small. All this snow sits on the January 13 melt/freeze crust that is still lingering in the back of our minds as a possible bed surface for a large avalanche, though triggering this would take more mass than a single skier can produce unless you find the trigger point over a thin spot.
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.
As we work through the conceptual model of determining avalanche hazard, our final comparison is looking at the likelihood of triggering an avalanche versus the destructive force of what could be produced. Much of our terrain, including areas where the wind slab problem currently exists, could produce a D1 sized avalanche which is defined as relatively harmless to people, a mass of less than 10 tons and a typical path length of 10 meters. Bear in mind this does not take into account the type of terrain you are in (getting knocked over a cliff, taken into a terrain trap, etc). Current surface wind slabs that are soft and thin and formed after January 25 fall into this category. Shift gears and now think about all the snow that sits on top of the January 13 crust. In isolated areas, this snow exceeds a meter in depth, places like below the headwall of Tuckerman, some of Gulf of Slides, areas of Oakes, think the direct lee of N through W wind. Should we see ice crusts lose some of their strength, the avalanche produced here would easily exceed the D1 category and produce an avalanche that runs a 100 meters and could bury, injure, or kill a person, a D2 avalanche by definition. While the likelihood of this avalanche occurring is unlikely, we feel that this possibility keeps our avalanche danger rating at Moderate today though in isolated areas.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch with good skiing most of the way down. 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 02/02/2020 at 7:11 AM.
USDA Forest Service
White Mountain National Forest
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