Avalanche Forecast for Tuesday, April 2, 2019
This information was published 04/02/2019 at 6:58 AM.
The Bottom Line
Small wind slabs formed since late Sunday could still produce a human triggered avalanche, and large areas of hard, refrozen snow make long, sliding falls a crucial risk to manage. The recently formed wind slabs should be avoidable in most terrain. Look for any new wind drifted snow in the alpine as the avalanche problem. While human triggered avalanches are unlikely today due to the isolated and avoidable nature of our current wind slabs, they are not impossible and you may be drawn to travel on these areas of softer snow. All forecast areas have LOW avalanche danger. A small avalanche or stumble on today’s hard refrozen crust could cause a high consequence, long sliding fall. Bring crampons, an ice axe, and your ability to use them to prevent a fall.
A trace of new snow yesterday morning was followed by clearing through the day. Wind on the summits decreased and shifted slightly from WNW at 70 mph to W at 40 mph. Temperatures remained below freezing in all of our terrain, with the Summit hovering around 0F. Today should be 15-20 degrees warmer at all elevations, increasing towards 20F on the summits and 35F at 3,500’ elevations. Decreasing wind may drop below 30 mph by this afternoon while shifting S. Below freezing temperatures tonight should refreeze any melting that occurs at middle and low elevations before tomorrow brings temperatures similar to today. Clouds move in overnight and will bring a chance of light precipitation tomorrow which should fall as snow at high elevations but as mixed precipitation and rain at middle and low elevations. Wind will increase significantly late tomorrow.
Primary Avalanche Problem – Wind Slab
Wind slabs from the 1-3” of snow since Sunday can be found in the terrain and especially on the eastern half of the compass rose. These small slabs can likely be avoided in many areas by travelling on the hard, refrozen crust. While we expect these pockets of wind slab are becoming stubborn to a human trigger, human triggered avalanches are not impossible and could cause a high consequence sliding fall. Variable recent snowfall across the range, with the Northern Presidentials receiving a little more snow, means that your evaluation of actual location and size of these wind slabs will be important 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.
Small amounts of snow fallen since Sunday has been affected by wind and presents the only distinct layer of concern in our present snowpack. Warming over the weekend thoroughly moistened the pre-existing upper snowpack which has since refrozen. Expect to find a snow surface of this robust melt freeze crust with areas of wind slab that formed in the past 24 hours. We expect the largest, though still relatively small, wind slabs to be in areas with a significant upwind fetch like the Headwall of Tuckerman Ravine and possibly in the Northern Presidential Range which has received slightly more new snow since Sunday. These wind slabs are gaining stability but should be respected and possibly avoided in high consequence terrain. Exposed melt freeze crust may see a little softening on sun exposed slopes this afternoon at middle and low elevations, but this softening is unlikely to be enough to for wet loose sluff to become a problem. Our lowest elevations like Crawford Notch are losing snow rapidly and some areas lack sufficient snow to have any avalanche problem.
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. Click here to check it out.
Recent snowpack and avalanche observations can be found here and on Instagram. Your observations help improve our forecast product. Please take a moment and submit 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 04/02/2019 at 6:58 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest