Avalanche Forecast for Saturday, March 7, 2020
This information was published 03/07/2020 at 6:56 AM.
The Bottom Line
You will find a variety of wind slabs in avalanche terrain on many aspects of the compass. Generally safe avalanche conditions exist. Watch for unstable snow on isolated terrain features today as yesterday’s inch of snow will have formed small wind slabs. Skiers should recognize that softer areas of snow are these isolated pockets. Long, sliding falls are possible today thanks to midweek wind scouring some of our terrain to icy surfaces or depositing pencil hard wind slabs that may require crampons for ascending. Even a small avalanche today could have severe consequences if you are unable to arrest a fall. Avalanche danger today is LOW: watch for unstable snow that could produce a small avalanche on isolated terrain.
Yesterday, the summit of Washington recorded 1.2” of snow with less than half an inch being recorded at each of our snowplots at lower elevations. This arrived during the late afternoon/evening and fell as wind direction shifted from S to NE. Wind speeds were around 20mph mid-afternoon and increased during hours of snowfall to the 40mph range.
Today will be clear with wind shifting from the current NE to NW by mid-afternoon. The current wind speed of 40mph should increase to 70mph and then drop back below 50mph for the evening. No snow is forecast today.
Tomorrow will be clear and windy, with gusts possibly exceeding 100mph in the morning. A slight chance of upslope snow exists in the afternoon.
Primary Avalanche Problem – Wind Slab
Small wind slabs formed from Friday’s inch of snow. These formed on easterly wind and will be found primarily on W through S aspects, but beware cross loading on other aspects. Watch for thin spots in the slab or softer snow that may be found near buttresses, rock outcrops, or trees as isolated pockets that could produce a small avalanche. Older wind slabs that formed mid-week have proven unreactive and lie primarily on easterly aspects. While these older slabs are largely hard, some softer areas can be found; that being said, the strength, structure, and energy of this older snow all point to good stability.
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.
First and foremost, today marks the start of the season for the Mount Washington Volunteer Ski Patrol. These volunteers provide rescue assistance, first aid, and skiing information to the public on weekends from now through Memorial. If you see a red jacket in the courtyard or in Tuckerman, please thank them for their time and be sure to ask for stories as many of these folks started patrolling when rear-entry boots were cool and 205 was a ski length, not a width.
Second, wind from the east is not rare for us, but certainly not the norm. The inch that fell on the summit yesterday fell on increasing wind from the NE. As you head into terrain today, bear in mind that routes normally used to manage wind slab formed on a westerly wind may be places that have isolated pockets of concern today. Good visibility today will either prove or disprove this theory as it was only an inch of snow, but as we all know, Low avalanche danger does not mean no avalanche danger.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. New snow from the week will provide good turns with some scoured sections.
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 03/07/2020 at 6:56 AM.
USDA Forest Service
White Mountain National Forest