Today should feel like a pleasant winter day, a break after two cold, windy days. Today, after nearly 48 hours of NW wind 50 – 70 mph, the wind shifts W and eases to 25 – 40 mph. Temperatures will also warm a little to the single digits F above zero. Skies will be clear to partly cloudy. Overnight and tomorrow temperatures will rise further to around 20F as W wind increases slightly 30 – 45 mph. Looking forward, there is no forecasted precipitation until Sunday.
Primary Avalanche Problem – Wind Slab
Wind slabs formed from the weekend’s storm will be stubborn to a human trigger and generally firm, with a few exceptions being softer in sheltered terrain. Terrain most exposed to wind will exhibit scouring to or near to the January 13th rain crust. You are most likely to encounter this problem on steep easterly slopes and cross-loaded gullies above 3500 feet.
Today’s avalanche problem of stubborn wind slabs is low probability but high consequence, meaning that complacency due to the lower likelihood of avalanches may lead you to travel in terrain which still could produce a large avalanche.
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.
Tuckerman Ravine, January 20, 2019
Field observations yesterday combined with the summit weather history of sustained 50 – 70 mph wind leads us to believe the relatively large wind slabs formed since the weekend’s storm are generally strong and stubborn (OBS1, OBS2). The supportive nature of these slabs can offer substantial bridging strength, reducing the likelihood of a human triggered avalanche. However, slow bonding due to cold temperatures, the presence of a weak (4F) layer sitting above the January 13 rain crust, and well developed slide paths are important factors to keep large avalanches a possibility today. Please be mindful that strong winds such as in recent days, create spatial variability making it less appropriate to apply stability test results across the terrain. You can find thick – stiff slabs, softer shallow slabs and scoured bed surface all in reasonably close proximity.
The largest slabs can be found well below the tops of avalanche paths, notably the lower half of Chute, Center Headwall, the Lip, and Sluice in Tuckerman Ravine.
Tuckerman Ravine, January 20, 2019
The Sherburne and Gulf of Slides ski trails are snow covered.
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 01/21/2020 at 7:07 AM.
USDA Forest Service
White Mountain National Forest
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