This information was published 02/03/2019 at 7:17 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
The chance of triggering an avalanche today is unlikely, but the risk of triggering an avalanche large enough to hurt and possibly bury you remains. Wind slabs are primarily in terrain with some degree of an easterly aspect. These can be easily identified from afar by their smooth white appearance or up close by their hollow sounds under your skis or feet. With a mid-winter snowpack now in place on the east side of the range, larger and more connected slopes are creating the potential for large avalanches today. The probability is low, though consequences could be dire. Due to the potential to find and trigger a thin spot in a large wind slab, MODERATE avalanche danger exists today. Some terrain, such as Left Gully and Hillman’s Highway may offer terrain with a degree of scouring that will allow you to avoid today’s avalanche problem. The Northern Gullies in Huntington are a good example of this as well and receive LOW avalanche danger. Smaller and more reactive wind slabs may also be found in isolated, wind sheltered areas.
Yesterday saw temperatures on the summit hover around 0F. West shifting WNW wind was in the 60-70 mph range with a 5-hour period late in the day when speeds increased to 85 mph. Observed snowfall in the afternoon brought a total of 1” of 10% snow to the summit with elevations at 3800’ receiving a trace. The current WNW wind of 54 mph will gradually shift due west and decrease to the 30-45 mph range by mid-morning. Temperatures will see a sharp increase today. The current temperature of 0F on the summit will reach into the teens F by noon, the 20sF by dark and likely above freezing by Monday morning. Elevations below 3500′ will see temperatures reach near freezing by early afternoon. As moisture moves into the region, clouds should develop through the day with precipitation possible late. Liquid precipitation equivalents will be low, under 0.1”, with a mix of freezing rain, sleet and snow likely.
Primary Avalanche Problem – Wind Slab
Firm wind slab exists in terrain on the eastern half of the compass. Areas in the direct lee of west wind and larger fetch contain wind slabs that could produce a large avalanche, particularly slopes that did not avalanche late last week (see observations of natural activity in Tuckerman, Huntington, and no activity in the Gulf of Slides). While these wind slabs have displayed signs of being stubborn to a human trigger, the cold temperatures have slowed the sintering process and instability lingers. Variability in thickness of the wind slab exists, leaving thin spots that will be hard to discern or areas of softer snow that skiers will likely be drawn toward. These are the places that provide the possibility of triggering today’s low probability, high consequence avalanche problem.
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.
The melt/freeze crust that formed January 25 has proven itself as a planar bed surface for avalanche activity. While natural activity has not initiated on the interface of this crust and snow above, many avalanches have stepped down to the crust, leading to the potential for large avalanches today. The wind slab that can be found is generally firm (finger to pencil hard) and supports a skier but may not support bare-booting. This wind slab has bridging strength, but it sits on top of a layer of soft snow (fist hard) that climbers have been plunging into. While the wind slab is strong, thin or softer areas that will provide trigger points do exist and may be places that you are drawn to today for quality of skiing or ease of uphill travel. Continuously evaluating the snowpack you are on and being prepared to alter plans will likely provide a good time in the mountains today.
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 02/03/2019 at 7:17 AM.
USDA Forest Service
White Mountain National Forest
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