This information was published 02/28/2020 at 7:00 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Dangerous avalanche conditions exist.
Natural avalanches are possible due to continued snowfall and wind loading today.
East-facing ravines that contain large, open snow slopes, like Tuckerman Ravine and Gulf of Slides, have the potential today to produce very large avalanches that could damage trees.
Limited visibility today will make just “going for a look” tough to pull off safely. If venturing into avalanche terrain today, an intimate knowledge of where each avalanche path can deposit debris will be crucial.
Avalanche danger is CONSIDERABLE. Cautious route-finding and even more so, conservative decision-making, is recommended today.
Yesterday was snowy with shifting wind. Snow totals from the around the Presidential Range were:
Washington summit: 9.5” with a SWE of 1.58”
Gray Knob: 7.8” with a SWE of 1”
Hermit Lake: 9.5” with a SWE of 1.7”
Wind yesterday started from the ESE with speeds around 90mph. Around 2pm yesterday, wind shifted to the W and has been stuck in the 70-90mph range since.
Today, snow showers will likely continue for the mountains, producing 1-3”. Wind will blow hard from the W, sitting at 60-80mph for the most of the day, perhaps decreasing slightly at times.
Tomorrow, it looks likely that upslope snow showers will continue, producing another 1-3”. Wind will start from the W and then shift NW, blowing 35-50mph for the day. Expect elevated avalanche hazard to persist.
Primary Avalanche Problem – Wind Slab
All snow at mid and upper elevations has been affected by wind, including sheltered areas in the trees like the Hermit Lake snowplot. Wind slabs have formed on terrain in the lee of our overnight W wind as well as cross-loaded into slopes that face N and S and will present with an upside down structure. Careful snowpack evaluation and stability tests are not really needed today. Instead, pay attention to the obvious red flags as more snow and more wind continue to stress these slabs today, possibly producing natural avalanches. Less snow in our lower elevation band lessens these concerns below 3500’, but watch out for wind slab development in Willey’s Slide and the top of Willard or Webster Cliff climbs today.
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.
Our wind affected snowpack often has short windows of peak instability. This recent storm was no different and we believe peak instability likely occurred last night. If you had whiteout vision goggles and could see terrain from afar today, it’s likely you would see evidence of an avalanche cycle in many places. In addition to debris piles and crowns, you’d also see significant wind loading and refilling of avalanche paths that already slid. Just because peak instability may have passed last night, this doesn’t exclude the possibility of avalanches today. Today will be a good day to let the Presidential Range adjust to the new load and do it’s thing while enjoying lower angled terrain.
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. 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 02/28/2020 at 7:00 AM.
USDA Forest Service
White Mountain National Forest
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