This information was published 01/28/2019 at 6:53 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Ideal wind speed and direction for loading easterly terrain has created wind slabs overnight that will continue to grow today. You are likely to trigger these slabs which are becoming large in size. Look for pillowy wind drifts and continued wind loading today to identify this avalanche problem. Some terrain, particularly at upper elevations on the west side of the range, may be scoured to the hard January 25th rain crust, which presents a long sliding fall hazard in addition to today’s avalanche problem. We have CONSIDERABLEavalanche danger today, with the Northern Gullies of Huntington Ravine and the Right Side of Tuckerman Ravine being the exceptions at MODERATE avalanche danger. Avalanches will be unlikely at lower elevations where today’s avalanche problem is generally absent.
Six inches of snow accumulation was recorded at the summit of Mount Washington yesterday, with 5” at our snow plots. This snow initially fell on S and SW summit winds in the 40-50 mph range. Wind shifted W and increased to 50-70 mph as snowfall tapered after dark yesterday. Wind should remain westerly around 60 mph before tapering off this evening. Summit temperatures will increase slowly though the day from the current -8F to the single digits above 0, and continue to rise through tonight to peak in the teens tomorrow. Cloud cover will decrease through the day today but increase again by tomorrow afternoon as another winter storm arrives. We may receive double digit snow totals by Wednesday.
Primary Avalanche Problem – Wind Slab
Wind slabs, which will continue to grow in size today, will be reactive to a human trigger. West winds loading lee terrain and cross loading other terrain will make this avalanche problem relatively widespread on the eastern half of the compass rose. New slabs will be largest in areas with large upwind fetch zones for wind to pull snow from, like the Headwall area of Tuckerman Ravine and east facing terrain in the Gulf of Slides. Be sure to account for this variability in size that is common with wind slabs as you make snowpack observations today.
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.
Five to six inches of new snow in the past 24 hours, which resulted from upsloping snow showers at higher elevations, has been affected by W wind in the 50-70 mph range since last night. These conditions produce wind slabs which can be much thicker than storm snow totals, often by a factor of 5 or more. Wind transport continues currently and slabs will continue to grow at least some through the day, though it is likely that instability peaked overnight. Instability in these new wind slabs, which continue to be stressed by new wind loaded snow, are the primary concern today with a few pockets of wind slab on similar terrain existing prior to the current storm above the melt/freeze crust formed last Friday. Stability concerns are limited to snow above this crust. This crust may be a player in potential avalanches today, but generally good bonding to the crust makes the weak layer of concern a density change or interface within snow deposited in the past 3 days.
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 01/28/2019 at 6:53 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
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