This information was published 03/16/2019 at 7:09 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
New snow and wind will build small wind slabs through the day today at mid and upper elevations. These wind slabs should remain unlikely for you to trigger in much of our terrain, but watch for these areas of new wind drifted snow to develop quickly with today’s weather. The wet slab avalanche problem of the past several days remains relevant today but will gain great stability as our snowpack refreezes. All forecast areas except the Headwall of Tuckerman Ravine have LOWavalanche danger, with MODERATEavalanche danger in and below the Headwall area.
This morning, watch for rockfall and icefall that will become less likely as the refreeze occurs. This refreeze will make long sliding falls a key hazard that demands respect. If you plan to travel on a snow slope today, be sure that your crampon and ice axe skills are dialed. Take care to not fall as our snow becomes increasingly hard and slick through the day, knowing that self arrest is at best difficult on refrozen snow.
Below freezing temperatures are returning to our terrain, though elevations well below 3500’ should hover right around 32F today. Summit temperatures will drop through today to 10F by dark and 0F by dawn tomorrow. This is a stark change from the past two days with high temperatures of 40F on the summit and close to 50F at our snow plots at 4000’ in elevation. A trace to 2” of snow, mostly at high elevations, may fall today with a greater chance at another 2” or more tonight. Snowfall amounts are uncertain but should taper by tomorrow morning. Wind is currently near 80 mph from the W on the summit and is forecast to shift NW and peak at slightly higher speeds this evening before slackening slightly by tomorrow morning.
Primary Avalanche Problem – Wind Slab
New snow today will be affected by W and NW wind. This wind slab problem does not exist this morning and will develop through today and more so tonight. Uncertainty in today’s snowfall amount and timing lend uncertainty to the timing, size, and sensitivity to triggers of developing wind slabs today. Watch for these small slabs on isolated terrain features and elevated avalanche danger tomorrow.
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.
Secondary Avalanche Problem – Wet Slab
Our snowpack is refreezing slowly today, but wet slab avalanches remain an unlikely though relevant avalanche problem this morning for middle and lower elevations. By late today or tonight, a solid refreeze at all elevations will stabilize our currently wet snowpack.
What is a Wet Slab Avalanche?
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
The period of melt since Thursday morning comes to an end with a refreeze and increasing stability today. Our wet upper snowpack will refreeze through the day by elevation, with colder temperatures up high freezing the snow sooner than low elevations. We expect a full refreeze at low elevations to occur tonight, making both flotation and traction devices advisable today. Stability concerns are becoming limited to the new snow arriving today. New wind slabs may develop from the several inches of snowfall today and tonight, though we expect these to be isolated in distribution with hard crust remaining the dominant snow surface. Long sliding falls have again become the key hazard to recognize and manage on snow slopes.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
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 03/16/2019 at 7:09 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
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