This information was published 03/07/2019 at 7:14 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Winter weather, with regular snowfall and cold temperatures, keeps wind slab avalanches on the list of mountain hazards that you will face today. These slabs have not had enough time or warm temperatures to settle and bond so evaluate the snow carefully today if you plan to venture on or below steep, wind loaded terrain features. While natural avalanche activity is unlikely, poor visibility will make it hard to tell what kind of snow exists above you or who may be in position to trigger an avalanche onto you. A mix of soft and firm wind slabs and scoured or wind-packed snow or ice exist throughout the range with the latter often present at or near the tops of gullies, making crampon use a good idea. MODERATE avalanche danger exists with human-triggered wind slab avalanches possible in primarily east facing, mid and upper elevation terrain. Snow stability will improve through the next couple of days.
Cold temperatures continue today with wind remaining strong from the west. The current temperature on the summit is -18F with winds near 60 mph from the west-northwest. Summit high temperature will reach only -10F today though winds will diminish slightly to 30-45 mph mid-day before increasing again into the 40-55 mph range with higher gusts. A trace of snow fell early yesterday morning with another trace to an inch possible this afternoon. Visibility will again be challenged by summit fog today. Temperatures will moderate significantly over the next couple of days.
Primary Avalanche Problem – Wind Slab
You are most likely to find reactive wind slabs in well-sheltered areas and beneath steep terrain features where 6” of snow has accumulated into thick slabs due to wind transport and sluffing action. Firm wind slabs that are likely to be stubborn but potentially much larger are also a concern in areas with greater exposure and a larger upwind fetch, such as across the east facing Headwall of Tuckerman Ravine and the major gullies of the Gulf of Slides.
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.
Runouts like this in Gulf of Slides are among the worst of the terrain traps that our range has to offer. Deep debris and flow fingers into adjacent trees combine to make this type of terrain trap as consequential as being swept off a cliff.
Natural avalanche activity on Monday, some of it large, highlights the fact that there are other slopes that are loaded but did not slide. These slopes and gullies, among other reloaded ones, contain larger slabs like the ones observed in Gulf of Slides yesterday that were firm (1F+) over much softer (F) snow. At risk of beating a dead horse, the snowfields and gullies around Mount Washington are really well developed. A topic of conversation with a solo skier yesterday highlighted the complexity of aggressive decision making in avalanche terrain. The intended target for him was Lobster Claw, presumably due to it’s safer or at least less-intimidating reputation than other objectives in the Bowl. As we sorted through list of concerns, such as the continued though minor wind loading and low visibility at the time, we also discussed the obvious disadvantages of solo travel. The other less obvious factor we talked about was that Lobster Claw, along with most gullies in Gulf of Slides, have what are likely to be some of the worst terrain traps in the range. These gullies all have constrictions that funnel debris deeply just before the debris spills out onto what is essentially flat ground. Observing these slide paths over the years has led me to understand that larger slopes with fanned out debris are preferable to the ugly death traps that exist beneath our less active avalanche paths, some of which, like the Lower Snowfields, have been running larger the past several weeks. Along with low angle traps, these less active paths also have more trees to run into if caught than more frequent runners like those across the Headwall. Long lived players in the avalanche arena consider the consequences of a slide and develop habits that will improve their chances of surviving an inevitable mistake in stability assessment or travel techniques.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. Thanks to those who have been submitting observations this week. These are very helpful to our forecast and the community so please keep them coming.
The Mount Washington Backcountry Ski Festivalis going off this weekend! Funds raised at the event support the efforts of the Granite Backcountry Alliance along with our efforts here at the Mount Washington Avalanche Center where we are facing increased costs associated with snow and weather data collection along with a general budget squeeze. Go check out a clinic or the presentations on Friday and Saturday night! We’ll see you there!
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 03/07/2019 at 7:14 AM.
USDA Forest Service
White Mountain National Forest
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