Avalanche Forecast for Tuesday, March 26, 2019
This information was published 03/26/2019 at 7:06 AM.
The Bottom Line
Wind slabs formed since Saturday remain possible for you to trigger today. Small wind slabs formed early yesterday are isolated but more likely to produce an avalanche, with large slabs formed over the weekend continuing to gain stability though still a concern. Keep the possibility of a human triggered avalanche in mind as you evaluate snowpack and terrain and continue to use safe travel practices of moving one at a time from safe zone to safe zone. Where the skiing and riding is good, you probably won’t be able to avoid the larger, older, and stubborn wind slab avalanche problem. The Presidential Range and most of Tuckerman Ravine has MODERATE avalanche danger. Huntington Ravine and the Left Side of Tuckerman Ravine have more scouring to older crust and have LOW avalanche danger.
One to two inches of new snow fell early yesterday in our middle and upper elevation terrain. West wind with a few hours of WNW blew in the 50-70 mph range, with clear skies for most of the day and summit temperatures hovering around 0F during daylight hours. Today is forecast to be similar, with clear skies and temperatures only a few degrees warmer. Wind will shift NW and may briefly decrease to under 40 mph on the summit before ramping up towards 60 mph this afternoon and evening. Temperatures should be around 15 degrees warmer tomorrow, with slightly decreasing wind, clear skies, and no precipitation.
Primary Avalanche Problem – Wind Slab
Large wind slabs formed primarily on Saturday continue to gain stability but still should be respected, while smaller wind slabs formed early yesterday are more likely to be human triggered. East and south facing terrain with an upwind fetch zone for wind transport, like much of Tuckerman Ravine, Gulf of Slides, and Oakes Gulf have very little scouring and essentially no opportunities to avoid the older large wind slabs. You’ll find pockets of the newer, smaller, and more reactive wind slab in the same terrain. Below 3,500’ in elevation, you’re unlikely to find unstable snow, but regardless of where you travel be sure to make good snowpack observations to guide your travel decisions.
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.
Wind slabs formed mostly since Saturday are above a substantial melt/freeze crust which formed just over a week ago. Good bonding to the crust was observed the past two days, with weak layers of concern generally limited to interfaces between layers above the crust. On the SE half of the compass rose you’ll find around one to four feet of snow above the crust, with a few thicker areas of wind slab and some scouring in particularly wind exposed terrain like Huntington Ravine. These now older wind slabs are stubborn and trending towards unreactive to a human trigger. Newer pockets of wind slab formed since early yesterday are more reactive to a trigger though isolated and not observed at more than a foot thick. As is typical with our heavily wind affected terrain, you’ll find spatial variability with the most consistent areas providing great turns to those who evaluate snow and terrain carefully.
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 03/26/2019 at 7:06 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest