Avalanche Forecast for Friday, March 8, 2019
This information was published 03/08/2019 at 7:06 AM.
The Bottom Line
Wind slabs exist in many places in mid elevation and primarily east facing terrain. The potential to trigger one of these slabs remains. A small amount of new snow yesterday afternoon combined with west winds blowing at loading speeds added to existing wind slabs. A MODERATE rating remains in all areas where wind slabs have grown this week. Careful evaluation of the snow and terrain should allow you to avoid triggering a large avalanche that could come from a few isolated areas in the steepest, most wind loaded terrain. Wind sheltered terrain on the west side is likely to have a similar wind slab problem though should be more isolated.
Cold temperatures, strong wind and another inch of snow on the summit kept winter firmly rooted in the high country. Wind gusts transported snow off and on through most of the day yesterday while summit fog allowed only brief views of more than a few hundred feet. The summit temperature will warm today to 5F from the current -11F. This morning’s west wind is blowing around 60 mph and will slacken for a while this afternoon as skies clear through the day. Overnight wind will be strong again in the 70’s mph but temps should remain above zero. Tomorrow looks to be sunny and clear with relatively balmy temperatures in the mid-teens with light NW winds.
Primary Avalanche Problem – Wind Slab
Cold temperatures and low visibility have kept folks from testing larger slopes, but limited ski and foot traffic have shown the wind slabs to be largely unreactive. Yesterday, the spooky structure of these slabs showed clean shears but no running cracks or other signs that propagation was likely. Very smooth and hard bed surfaces lie beneath the new wind slabs which complicates travel and reduces bridging opportunities for slabs in steep gullies or on unsupported slopes.
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.
Some early faceting was observed in sheltered terrain alongside a gully feature in Gulf of Slides. Though these grain types aren’t likely to be widespread enough to create a stability concern, their existence does point to the fact that cold temperatures have not been improving stability and may even be reversing the sintering process. As noted above, a hard bed surface is lurking beneath the patchwork of new wind slabs formed this week, creating skinning challenges at times and making crampon use a good idea lower on a slope than you might think. These bed surfaces are by and large edgeable but will have me carefully considering my runout should I trigger a pocket or even pre-release from a binding on the variable and sometimes grabby snow. Sheltered areas of snow provided some good turns yesterday but scouring will continue to keep things technical in steeper terrain.
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 on Friday and Saturday night! We’ll see you there!
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 floatation 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 03/08/2019 at 7:06 AM.
USDA Forest Service
White Mountain National Forest