This information was published 01/26/2019 at 7:03 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Small pockets of wind slab that you may be able to trigger can be found in our terrain, but refrozen icy snow presents an equal or greater travel concern today. Arresting a fall in steep terrain may not be possible. As you choose terrain today, consider the consequences of a long sliding fall, which could be caused by a simple stumble or even a very small avalanche. Crampons, ice axe, and strong ability to use them are essential tools for our current conditions. Refreezes also result in variable conditions on our ice climbs. Brittle ice and ice dams are likely. Avalanche danger for all forecast areas is LOW.
Increasingly cold temperatures and small amounts of snowfall have occurred since Thursday’s significant rain and warming event. Approximately 1” of new snow has been recorded at our snow plots in the past 24 hours. This snow has been affected by W wind blowing up to the 50-70 mph range for several periods. We should see a wind decrease from the current 40 mph by this evening, with temperatures on the summit remaining in the single digits below 0F. Partially to mostly cloudy skies with summit fog may produce a few snow showers today with little if any accumulation. Tomorrow is forecast to be a few degrees warmer, with a weather system arriving to bring 3-5” of snow on S wind.
Primary Avalanche Problem – Wind Slab
Wind slabs that are small in size may be reactive to a human trigger, but should be sufficiently isolated in distribution to be easily avoided We expect that west wind has scoured the small amounts of recent snowfall from much of our terrain and built these isolated slabs. This avalanche problem will not be present in most terrain. Realize that a small avalanche in the wrong place, which could simply be a steep and slick snow slope today, can still have big consequences.
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.
1-2” of snow has been recorded at our manual snow plots in the past 48 hours. In the same period, our snowpack has been refreezing in the wake of Thursday’s wetting and warming event. Visibility has been limited at best since before Thursday, but we’re confident that the refrozen snowpack is quite stable. Small wind slabs formed on westerly wind in the past two days are our only avalanche concern. You’ll likely find the refrozen snow to be quite supportable in the alpine, where hard snow preceded the rain event, and a breakable crust at lower elevations. Climbers will find good cramponing conditions, while skiers might be better served by machine groomed slopes today. Be on the lookout for any drifts of new snow that are today’s avalanche problem and be sure to respect the slide for life conditions.
The Sherburne and Gulf of Slides ski trails are icy but with coverage 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 01/26/2019 at 7:03 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
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