This information was published 04/11/2019 at 6:59 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Temperatures have continued to fall since yesterday resulting in a sketchy mix of wind scoured, bulletproof ice crust and fresh wind slabs. Areas that contain these wind slabs have MODERATE avalanche danger due to the possibility of a human triggered avalanche. Steep terrain without well-bonded new snow will have a significant sliding fall hazard. Don’t count on arresting a fall on the icy surface beneath this new snow. Even a small avalanche can cause a significant problem today. A brief window of sunshine and warm temperatures may bring some softening this afternoon but consider your options if it does not. And bear in mind that the new wind slabs will weaken if and when they warm today.
Snow showers continued yesterday and overnight, depositing another inch of snow at higher elevations for a 48 hour total of 3”. During that time, WNW and NW winds continued to transport snow on 45-60 mph winds. Skies have cleared today after two days of fog. Wind will diminish as well, possibly all the way down to 15-20 mph by afternoon. The current temperature on the summit is 5F with 13F at Hermit Lake. The forecast high temperature for the summit is 23F. Warming will continue overnight and tomorrow as southwest flow brings rain by tomorrow night.
Primary Avalanche Problem – Wind Slab
Wind slabs up to size D1.5 or even size 2 may be possible in east facing bowls like Tuckerman, Huntington, Gulf of Slides and possibly the Great Gulf. They’ll be thickest in upper start zones and will likely be in the stubborn to reactive range. Expect a poor bond to the icy bed surface until proven otherwise, especially in steeper terrain and on unsupported slopes.
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.
True to form, the expansive fetch of the Bigelow Lawn and Alpine Garden produced ample amounts of snow to build wind slabs out of a paltry amount of snow. Forty eight hours of W and NW winds efficiently moved this snow around the mountain and refreshed our still wintry snowpack. Limited visibility and active wind loading kept us out of steep start zones yesterday but the feedback we received while standing in boot-top drifts was sufficient to develop a wait-and-see opinion on skiing anything steep. The icy bed surface from Monday’s sleet, snow and freezing rain mix was well on it’s way to a deep solid freeze with -7C on the surface gradually warming to 0C down 15cm. At this point, it’s locked up tight. As temperatures warm, the new wind slabs will weaken, ultimately passing through peak instability as a wet slab avalanche problem tomorrow before becoming a part of an isothermal snowpack.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
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 tosubmit 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 04/11/2019 at 6:59 AM.
USDA Forest Service
White Mountain National Forest
Sign up to get the daily MWAC avalanche forecast in your inbox