This information was published 03/01/2019 at 7:19 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Cold temperatures have slowed settlement of the large wind slabs formed during Monday’s snow & wind storm. Generally speaking, these wind slabs are firm enough to support the weight of a skier or climber and triggering an avalanche is unlikely. The avalanche danger is LOW in all forecast areas today. However, unlikely does not mean the same as impossible so it is worth considering today that our steepest and most sheltered areas hold thick, wide wind slabs that push the upper end of the LOW rating due to their size. You’ll find the largest of these slabs in the usual east facing places including the Headwall of Tuckerman Ravine and the Gulf of Slides.
Tuckerman Ravine 2/27/2019. Wind slabs appear smooth and pillowy in some areas, heavily wind textured in others.
Be mindful that our deep snowpack has allowed the normally smaller snowfields to grow in size and should be on your radar. If you’re out today, enjoy the nice weather but don’t let your guard down. Also, bear in mind that the snow is really firm so the potential for long sliding falls should have you thinking about crampons, and an ice axe. Moving carefully and assessing obstacles in your fall line will reduce your risk to this hazard.
Today is forecast to be another pleasant day with light W winds of 20-30mph and a summit high temperature of 10F, a nice increase from yesterday’s high of 3F. A low pressure system to our south will slide in, increasing overhead clouds through the day with the summits expected to remain in the clear. Tomorrow will be slightly warmer with temperatures in the teens, continued low wind speeds and increasing clouds leading to a chance of light snow in the afternoon.
Primary Avalanche Problem – Wind Slab
Wind slabs formed from the three days of high of wind following Monday’s snow are generally firm in middle and upper elevations. Expect them to be unreactive to a human trigger, but look for exceptions to help guide your terrain choices. Be especially careful of smooth slabs that sound hollow or are soft underfoot. These slabs vary in size and are quite large in some terrain, particularly the Headwall of Tuckerman Ravine. This avalanche problem should be generally absent on the western half of the compass rose. In lower elevations you’ll find pockets of snow with a poor structure that may be more reactive to a human trigger though smaller in size.
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.
Lower Snowfields. 2/27/19. Snow sloughing from Dutchess collecting under the gully on the left side of the Lower Snowfields. Sections of the crown from a recent natural avalanche in the Lower Snowfields still visible.
Some say that wind is the architect of the snowpack, and nowhere is this more true than on Mount Washington. The 8” of new snow on Monday has been ravaged by consistent wind as high as 171 mph. In the aftermath we find areas of smooth and hard (1F – P) wind slab, heavily wind textured snow, and scouring. When we see wind speeds this high, the slabs tend to form much lower on the slopes and this was evidenced by crown lines remaining from natural avalanches in the Lower Snowfields and a very low snow slope on the north side of Raymond’s Cataract. Interestingly, field observations did not show signs of natural avalanches from the usual performers. With plump slabs below many of our large avalanche paths it appears more likely that they continually sluffed snow throughout the storm, possibly due to such high wind speeds.
Wind sculpted sastrugi in the drainage as you exit the floor of Tuckerman Ravine.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. The Little Headwall filled in during the storm though it is guarded by large and aggressive sastrugi snow in the drainage.
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 03/01/2019 at 7:19 AM.
USDA Forest Service
White Mountain National Forest
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