Avalanche Forecast for Wednesday, February 19, 2020
This information was published 02/19/2020 at 7:05 AM.
The Bottom Line
Howling wind will move snow from the ground into eastern ravines and gulfs. Wind slabs will exist today on multiple aspects due to the shift in wind direction. CONSIDERABLE avalanche danger exists on northerly through easterly aspects of the range. Very large and far running dry slab avalanches are possible in Tuckerman Ravine, Hillman’s Highway and to a lesser extent in the Gulf of Slides. In these and similar locations, slopes could avalanche naturally due to the stress of continued wind loading.
- Dangerous avalanche conditions exist in and below wind loaded terrain.
- Human triggered avalanche are likely today.
- Keep your terrain choices conservative, or better yet ski, ride or climb in wind sheltered lower elevation areas.
- Avalanche danger is likely to be reduced by tomorrow as slabs become stubborn.
Yesterday, the passing low favored the southeastern part of the range 7” or more snow falling there, 4” recorded on the summit of Mount Washington and 5” at Hermit Lake. Wind yesterday was from the south in the 50-70 mph range from noon to midnight but was much lighter in the 20-40 mph range at the beginning of the snowfall.
Today, howling winds which shifted from the south to the west around midnight, will shift again to the northwest and increase in speed even more mid-day. Wind is currently blowing near 80 mph with gusts over 100 mph. Continued snow showers and blowing snow will reduce visibility with another inch or so expected to fall. Temperatures are currently cool but will grow much colder, bottoming out at -21F on the summit tomorrow morning. Currently it is 8F on the summit and 30F at Pinkham Notch.
Tomorrow, wind will continue from the northwest and will subside to the 70-90 mph range in the morning, 50’s mph around midday.
Primary Avalanche Problem – Wind Slab
The wind speeds that are forecast will eventually pound snow into stubborn, hard wind slabs but not until we pass through a period of peak instability. Wind slabs exist on multiple aspects due to the southerly wind direction followed by a shift to the west and northwest. Blowing snow will make it challenging to identify areas of scouring versus loading. Hollow snow or areas of deep accumulation could fail under your weight.
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.
Snow rangers responded yesterday to a solo hiker in Tuckerman Ravine who sprained his ankle after a night out on Nelson Crag. This person hiked down Right Gully and beneath the Lip of the Tuckerman Ravine headwall. I bring this up because vacation week and Presidents Day weekend brings lots of visitors to the area who may not know the area very well. If you decide to brave the wind today in an attempt to thread the proverbial needle of our avalanche paths, remember that there may be other triggers on slopes above you. The bright and shining red flag signaling avalanche danger today may not be noticed by the unaware. Today isn’t the day to go have a look around and put yourself in the crosshairs of avalanches from above.
The Sherburne and Gulf of Slides ski trails are snow covered with fine riding 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 02/19/2020 at 7:05 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest