This information was published 04/28/2019 at 7:04 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Snow that fell Saturday combined with increasing wind to create wind slabs that will be possible to trigger and could produce an avalanche large enough to fully bury a person. Cold temperatures have refrozen our previously wet snowpack, creating the potential for long, sliding falls that make bringing an ice axe and crampons as important as avalanche rescue gear. If you find good skiing today, it means you are on a wind slab and in the the middle of today’s avalanche problem. Further complicating travel today will be the glide cracks and moats that formed over the past week. New wind slabs will likely have covered some of these open holes in the snowpack, but not bridging the hazard, meaning they’re now just hidden from view. With the trifecta of hazards in play today, keep terrain simple and realize that an avalanche today has more potential to result in harm than on a mid-winter snowpack.
The Mount Washington Avalanche Center will no longer issue daily avalanche forecasts for the 2018/19 season. Instead, we will post an updated General Bulletin as needed, in case of significant snow or weather events that might vary from the typical daily changes that come with spring weather. We will also keep you informed about the official closure of the portion of the Tuckerman Ravine Trail where it passes by Lunch Rocks and through the Lip and above the Headwall as well as the switch from the Lion Head Winter Route to the summer trail. Observations from the field will continue to be a valuable resource, so please keep submitting photos, videos and observationshere and we will do the same. Check the Forecast page for update on Sherburne Trail closures, which are imminent as spring snowmelt continues.
The switch to a General Bulletin does NOT mean that the mountains are now a safe place to ski. The hazards which emerge in the spring are significant and require careful assessment and strategic management. If you have never skied Tuckerman, peruse our Incidents and Accidents pages for spring related incidents involving avalanches, long sliding falls, icefall, crevasse and moat falls, and other incidents related to diurnal changes in the snowpack. These will help you understand and plan for these hazards.
After a rainy start to the weekend, snowfall at high and mid elevations Saturday produced 2.3” at Hermit Lake, 4.3” at Gray Knob, and 3.8” on the summit. During the period of snowfall, wind started from the west at 30mph and increased to 70mph, still from the west. Currently, Sunday morning, wind direction is shifting to the NW and should decrease through the day. Cloudy skies should linger Sunday with a chance of snow, but visibility should improve. Temperatures should stay below freezing above 3500’. Monday looks to start with sunny skies and then develop clouds with ambient air temperatures staying below freezing. Tuesday and Wednesday will see a possible round of precipitation, though temperatures will be pushing toward the freezing mark.
Primary Avalanche Problem – Wind Slab
Wind slabs will be possible to trigger and in places have the potential to produce a large avalanche. Keep in mind that wind can transport snow very efficiently and we often see wind slabs 5 to 10 times thicker than the amount of snow that fell from the sky. These will thinly cover previously existing glide cracks and moats, hiding these holes from view but not providing any bridging over the underlying hazard.
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.
Despite a snowpack laden with glide cracks, moats, and undermined snow, winter in the high country is not over yet. Significant melting over the past two weeks has allowed the multitude of springtime hazards to present more challenges to recreationalists than avalanche hazard. Below freezing temperatures at upper elevations will slow the rate of melting and reduce the likelihood of some hazards, but the following should play into travel decisions, particularly those which are now covered with newly formed wind slabs:
Steep snow and ice in gullies and trails, such as the Lion Head Winter Route, becomes very hard when the lower snowpack layers emerge with melting or when we see a hard refreeze of the snowpack like Sunday is presenting. Currently, the Winter Lion Head route as well as areas of the snowpack that were scoured by the wind are icy and require crampons and an ice axe to climb with any security.
The Sherburne and Gulf of Slides ski trails are no longer completely snow covered to Pinkham Notch. Expect ice, open stream crossings, rocks and bare patches. We will likely be closing a lower section of the Sherburne soon in order to prevent destructive erosion of the trail. When we do, please do your part to preserve the quality of the trail by removing your skis and hiking the rest of the way down to Pinkham on the Tuckerman Ravine Trail.
The young man who was last seen heading up the Winter Lion Head Route on March 8 remains missing. It is thought that he may have been intent on taking his own life. If that is the case, his remains may be somewhere with the Cutler River Drainage, around the summit or within a few hours hike on the steep part of Lion Head Winter Route. Please report any potential clues to the NH Fish and Game officers at 603-271-3361 or to USFS Snow Rangers at firstname.lastname@example.org or via AMC Front Desk staff at Pinkham Notch Visitor Center. If it is clear that you have found him, please call 911.
Details on daily snowfall totals, precipitation type, total depth of snow and other information can be found on our page devoted to snow study plot data. Clickhere to check it out.
Recent snowpack and avalanche observations can be foundhere and on Instagram. Your observations help improve our forecast product. Please take a moment andsubmit a photo or two and a brief description of snow and avalanche information that you gather in the field.
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 04/28/2019 at 7:04 AM.
USDA Forest Service
White Mountain National Forest
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