Avalanche Forecast for Friday, February 21, 2020
This information was published 02/21/2020 at 7:05 AM.
The Bottom Line
While human triggered avalanches are possible today, snowpack evaluation and terrain management will provide ample recreation for those looking to ski and climb. Wind drifted snow exists on many aspects and has a MODERATE rating for the day. Be wary of convex or unsupported snow slopes as you move around. If the snow underfoot changes from supportable to postholing or “grabby” skiing, it’s probably time to take another look at where you are and investigate why the snow structure suddenly changed. Places that have been scoured by this week’s wind may lack today’s avalanche problem and offer generally safe conditions.
Yesterday, no snowfall was recorded. Temperatures remained below 0F above 4000’. Wind shifted between W and WNW, starting the day at 70mph and gradually decreasing to 35mph, where it currently sits.
Today, expect mostly sunny skies. Current below 0F temperatures should gradually warm through the day to 5F on the summits by sunset. Wind will increase to above 50mph from the W.
Tomorrow should start clear with strong wind from the W. Upslope snow showers may produce a measurable amount of snow in the afternoon and nighttime. Temperatures will increase significantly on Sunday. It is possible that everything under 5500’ will go above freezing.
Primary Avalanche Problem – Wind Slab
Firm, stubborn wind slabs exist on many aspects due to varying wind direction mid-week. Expect to find several interfaces and layers of new snow when you dig today. While propagation was minimal in limited field time yesterday, the spatial variability encountered demanded getting hands in the snow to see what each slope consisted of. You may find thinner wind slabs in protected areas that are more susceptible to triggering. The outside chance of a large avalanche is unlikely today, though the size of the natural avalanche cycle that occurred Tuesday into Wednesday should provide a reminder of what is possible and that we are finally in a fully developed snowpack.
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.
It’s been a rough past few days to get in the field thanks to the combined forces of wind and cold. Because of this, a degree of uncertainty exists in today’s avalanche forecast. History has shown us that when wind blows as long and as strong as it did, we are usually left with a mix of scoured ice, sastrugi, and unreactive wind slab. A brief trip into terrain yesterday afternoon confirmed some of these suspicions, but not enough for us to say unreactive with confidence. Today’s improved weather will likely drive people into terrain and hopefully you send us your feedback through our observations page.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch and are skiing just fine.
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 02/21/2020 at 7:05 AM.
USDA Forest Service
White Mountain National Forest