Avalanche Forecast for Sunday, March 3, 2019
This information was published 03/03/2019 at 7:09 AM.
The Bottom Line
Wind slabs remain our primary avalanche problem today. LOW avalanche danger exists throughout the forecast area though the potential for small avalanches remains in isolated areas. Human triggered avalanches in these wind slabs are unlikely but not impossible. Normal precautions in your terrain management as well as in the gear that you carry is advised. The firm slabs in steep open terrain present a long sliding fall hazard so crampons, an ice axe, and an honest assessment of the consequences of a slip will also be useful today.
Around an inch of low density snow fell on the summit overnight and early this morning on moderate (40’s mph) summit winds from the WNW. Temperatures are starting in the single digits above zero and will rise to the teens on the summit and around freezing in Crawford Notch. Skies will clear and winds will diminish further today as high pressure passes by before tonight’s storm. Snow will begin shortly after dark tonight. Though most weather models show the low pressure tracking far enough off shore to keep snow totals on the modest side, between the storm and the upslope snow that follows we will have elevated avalanche danger tomorrow, especially as the west and northwest winds increase.
Primary Avalanche Problem – Wind Slab
Wind slabs may also be found at lower elevation locations and have presented clean shears though no sign of propagation has been evident since their formation in the extreme wind event on Feb 25th. At mid elevation areas, most of these wind slabs are firm and unreactive. There have been multiple observations of an upside down snow structure, particularly at lower elevations or some wind sheltered locations, but with no reports of significant cracking or collapsing. Wind sheltered terrain may contain softer wind slabs that are more stubborn than unreactive, so be increasingly cautious where hollow sounding snow and steep terrain intersect.
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 that fell at higher elevations last night, like the light snowfall on Wednesday night, is unlikely to improve skiing conditions. The softest snow is found either at lower elevations or wind sheltered areas. Snow coverage has improved on the west side with an avalanche observation in the main gully of the Ammo recently which helped to fill in and cover some obstacles. The snowpack there remains thin with open water and the typical terrain traps in place. Lots of lines have been skied this week throughout the range, though no huge, soft snow induced grins have been observed. Technical ski mountaineering with careful crampon and ice axe equipped ascents, followed by cautious, short radius turns on the way down paints a clearer picture of what’s been happening. It’s not even close to spring yet at any elevation with a dynamic snowpack that continues to demand respect. Crowds of people on the Lion Head winter route are being reported so factor in wait times on the steep sections into your itinerary or consider an alternate route.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. Thanks to those who have been submitting observations this week. These are very helpful to our forecast and the community so please keep them coming. Some issues involving iPhone photo uploads have been resolved so the sideways photo problem is no longer a problem.
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 03/03/2019 at 7:09 AM.
USDA Forest Service
White Mountain National Forest