Avalanche Forecast for Saturday, March 9, 2019
This information was published 03/09/2019 at 6:59 AM.
The Bottom Line
It is possible for a skier or climber to trigger an avalanche today in wind loaded terrain. Natural avalanches are unlikely, but consider the increased power from the sun as spring approaches. Wind slabs on steep slopes with a southerly aspect can weaken subtly as winds diminish and temperatures warm. Wind slabs exist primarily on slopes with a degree of easterly aspect at mid-elevations, including some terrain and micro-features on the west side of the range. A MODERATE rating is given to today’s avalanche problem due to the possibility of human-triggering combined with the potential size of an avalanche. The exception to this is the Northern Gullies in Huntington which have LOW avalanche danger. Careful terrain selection that combines terrain management with the human factor (within your party and others) will improve your odds for a safe day in avalanche terrain today.
Friday was a great winter day for those who took advantage of it. Temperatures moderated to around 10F with W and WNW wind in the 40-55 mph range. Clear skies allowed great visibility and the blowing snow that contributes to our wind slab problem could be seen at times streaming down from our alpine fetch. High pressure cresting over the region today will continue this trend with temperatures on the summit reaching into the teens F, skies remaining clear, and wind decreasing from the current NW 60 mph to 15-30 mph by the end of the day. The approaching warm front will arrive after dark tonight, with precipitation starting in the wee hours of Sunday morning. By Monday morning, 6-8” is possible, though expect sleet to mix in at higher elevations and maybe rain below 3500’.
Primary Avalanche Problem – Wind Slab
Wind slab is prevalent on easterly aspects at mid-elevations. The structure is fairly simple: firm slab that is 5-15” thick over a thin layer of much softer snow acting as the weak layer, with a variety of smooth bed surfaces underneath. Shooting cracks and whumphing have been absent for the past several days, but tests are producing fairly clean shears with some indicating the ability to propagate a crack. While ambient air temperatures will stay below freezing today, clear skies will allow ample solar radiation as the day progresses. Steep slopes that have a degree of southerly aspect will likely see warming effects today. This red flag is hard to gauge the impact of and has produced some strange avalanches. The best way to treat the first real warming of a wind slab like we will see this afternoon on slopes such as The Lip and Sluice is to give them a wide berth of respect, minimizing any time you choose to spend on or beneath them.
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.
Hard bed surfaces that range from ultra-firm wind slab to melt-freeze crusts are exposed in places that wind has been able to scour. While edgeable, the widespread distribution of some sort of firm layer makes bringing your crampons today a no brainer. This is also providing the bed surface for our avalanche problem. Skiers and climbers yesterday found that the wind slab was in places supportable while booting, but more often punching through. With skis on, this wind slab offered decent skiing, but where the slab was thinner, it was described as punchy. In addition to providing more challenging skiing, these thin areas also proved more capable of producing an avalanche as one skier found in Right Gully. Terrain management may prove challenging today with the combination of good weather and the Mount Washington Backcountry Ski Festival. Expect crowds and skiers to drop in from above with no warning.
The Mount Washington Backcountry Ski Festival is going off this weekend! Funds raised at the event support the efforts of the Granite Backcountry Alliance along with our efforts here at the Mount Washington Avalanche Center where we are facing increased costs associated with snow and weather data collection along with a general budget squeeze. Go check out a clinic or the presentations tonight at Theater in the Woods! We’ll see you there!
Are you in need of a new airbag backpack? We’re auctioning off two Black Diamond Saga 40 Airbag packs. Check out the auction here!
The Gulf of Slides and Sherburne ski trails are snow covered to Pinkham Notch. Please be courteous and don’t walk on these trails or in any other skin tracks without snowshoes or some kind of flotation on your feet.
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 03/09/2019 at 6:59 AM.
USDA Forest Service
White Mountain National Forest