Avalanche Forecast for Wednesday, March 6, 2019
This information was published 03/06/2019 at 7:23 AM.
The Bottom Line
Slopes with large areas of wind drifted snow could produce an avalanche from a human trigger today though natural avalanches are unlikely in all areas. The Headwall of Tuckerman Ravine and the Southern Gullies in Huntington hold the largest of these new wind slabs. These slabs are likely to be stubborn though a human-triggered avalanche on the larger side remains possible here following the wind loading that occurred yesterday and overnight. All forecast areas have MODERATE avalanche danger, with the Northern Gullies in Huntington Ravine as the exception with LOW avalanche danger. Be mindful that the soft snow you may be seeking is the avalanche problem today, and the old bed surface is firm requiring careful footwork with crampons.
Just under and inch of new snow fell at higher elevations overnight on 40-50 mph W wind with cold temperatures that bottomed out at -15F. Today will be another unseasonably cold day with a high temperature in the teens below zero. The current 35-50 mph W wind will increase later this afternoon with gusts to 75 mph. Summits will remain mostly in the clouds with a chance of snow showers and up to an inch of new snow. Tomorrow is forecast to be cold as well with a high of -10F and another chance for snow showers.
Primary Avalanche Problem – Wind Slab
Wind slabs formed in the last 24 to 48 hours are the primary avalanche concern today. These slabs are generally firm and stubborn with softer and reactive pockets in wind sheltered terrain. These new slabs will be found primarily in start zones in the middle or lower areas of slopes and gullies in the ravines on the east side of the range.
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.
Our snowpack is a mix of new wind slab, and old bed surface. Stability tests yesterday low in Huntington Ravine and Tuckerman Ravine demonstrated moderate results, though only in the most wind protected locations. Generally the new slabs were firm (P) to the bed surface and likely to be unreactive in all but isolated areas in steepest terrain. Many places in our terrain are also wind scoured making skinning difficult and crampons useful. Pockets of wind slab can be a problem especially over steep or rocky terrain or terrain traps like you might find in west side gullies.
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.
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 03/06/2019 at 7:23 AM.
USDA Forest Service
White Mountain National Forest