Avalanche Forecast for Monday, March 16, 2020
This information was published 03/16/2020 at 7:10 AM.
The Bottom Line
Conditions that create a long sliding fall hazard persist. Warm rain followed by a re-freeze Friday night has left most of the open snowpack firm, icy and smooth where an unexpected stumble can lead to sliding downhill at an accelerating rate that quickly becomes too fast to self arrest. Mitigate this hazard in steep terrain by using tools that keep you firmly connected to the snow including crampons, ice axe, and rope belay where appropriate.
For skiers and snowboarders looking for sun softened snow, south aspects may soften today, or they may not. If they do soften a little, it may not be enough to eliminate the sliding fall hazard, and remember that once the afternoon sun passes the softened snow will very quickly flash freeze. Avalanche danger is LOW today.
Yesterday, an overcast morning cleared to blue skies with temperatures reaching 7F on the summit of Mt Washington and 28F at Hermit Lake. Wind from the NW was moderate and consistent at 35 to 45 mph for the daylight hours. Bright sun may not have been enough to soften snow on southern aspects.
Today, another day of clear skies and temperatures in the single digits F. North west wind will shift SW midday at 15-25 mph and increase to 30-45 mph and higher after dark. Up to an inch of snow is possible tonight from snow showers.
Tomorrow snow is forecast to begin before sunrise and continue through the day with 1 to 3” or more at higher elevations from almost 0.5” of water. Wind is expected to be from the S for roughly the first half of the storm, shifting W for the second half of the storm. Temperatures on the summits will reach the lower 20sF. At this time, it looks like the freeze line will be around 3500’. Locations below 3500’ will see some rain as temperatures warm midday. Avalanche danger will increase if we see the upper end of possible snow totals.
Primary Avalanche Problem – Wind Slab
Thin wind slabs can be found in locations that were protected from the extreme winds Friday and Saturday. In some areas these wind slabs will be firm and unreactive, and in other locations they will be encased in an ice crust with a softer layer of snow beneath. Areas that were scoured from the wind will be very firm, icy and smooth.
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.
Long sliding falls are a significant hazard in our terrain after a rain and re-freeze. We include a list of accidents on our website as a learning tool for others. It’s helpful for all of us to read about the mistakes of others, reflecting on the decisions we make, and maybe even exposing a bad habit or two such as not putting crampons early or leaving your helmet on your pack for the climb. We also have a separate list for long sliding falls, since we see them often, and can be especially dangerous:
Yet to be added to this list: yesterday afternoon the Hermit Lake Caretaker and a Snow Ranger assisted a skier who fell and slid the full length of Right Gully in Tuckerman Ravine. His injuries required transportation to the road and an ambulance to a local hospital.
Please take a few minutes to read through this list and remember that the simple steps we talk about often, including using crampons, stiff boots, ice axe and understanding the limits of practiced self-arrest can help keep you safe, making your day more fun.
Thanks to this observation that pointed out slick conditions above the ravines.
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 03/16/2020 at 7:10 AM.
USDA Forest Service
White Mountain National Forest