General Bulletin for Wednesday, December 7, 2016

This bulletin will expire at 12:00 midnight on Friday, December 9, 2016.

General Bulletins are issued when isolated areas of unstable snow exist within our forecast areas. Forecasts using the 5-scale danger rating system will be issued when snowfields and bed surfaces develop further. Please remember that avalanches can occur before a 5-scale forecast is issued. A new General Bulletin will be issued if conditions warrant or within 72 hours.

Winter delivered 27.8″ of snow to the summit of Mount Washington since December 1. For comparison, last December the summit recorded 29″ over the entire month. Over the past two days, 7.5″ fell on NW winds averaging 34 mph.  Late on Sunday, winds diminished to the teens and swung to the south, eventually regaining strength and returning to NW, maxing out at 67 mph early on Tuesday, December 6.This shift in winds is evident in the current snowpack with multiple fist to finger hard layers under wind slabs which formed on lee slopes. Field work Tuesday showed lingering instabilities that make safe travel in our forecast area challenging at the moment. Snowfields are growing, but are still broken up by rock buttresses and ice floes in some areas. With the snowpack that currently exists, triggering a small pocket in either ravine would have dire consequences due to rocky and shrub filled runouts. Snowfields are currently the largest in Left Gully and the Chute in Tuckerman and North, Damnation, Yale, and Central in Huntington. Debris under Left and the Chute is clear evidence that avalanches can occur under a General Bulletin and that travelers should have their avalanche skills in hand when entering terrain.

Low pressure building from the Great Lakes will send a cold front toward New England over the next few days that should deliver another round of snow. Ten inches of new snow on the summit by Friday is forecast with conditions prime for upslope snow events. Winds will be starting today, Wednesday, SW 15-30 mph shifting to the W by nightfall. By Friday morning, we may see winds increasing to 70 mph, bringing us up to and through the prime speeds for loading slopes. As the Bigelow Lawn and Alpine Garden are well filled in right now, this smooth fetch will allow snow to blow into our forecast areas, creating an upside down windslab. These wind slabs will sit atop a buried layer of graupel that can be found on multiple aspects in both ravines.  Snowfields will continue to grow and will become capable of larger avalanches. Just a week ago, it still seemed like fall; now it’s looking like we’re moving quickly into full-blown winter.

Below Hermit Lake, travel is still affected by the construction taking place on the Tuckerman Ravine Trail. The trail remains closed for a section and it is recommended that hikers use the detour on the lower Huntington Ravine Trail and Raymond Path. For those skiing and riding the Sherburne, be prepared for variable conditions (powder, scoured old surface, open water bars, mud, and ruts and rocks turned up from the snowcat in operation for the construction crew.) Please be on the lookout for heavy equipment traveling to and from the construction site. Also be aware of the old bridge debris temporarily piled at the junction of the Sherburne and #7 Crossover.

Please Remember:
• Safe travel in avalanche terrain requires training and experience. This bulletin 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.
• Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast. For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin.
• Posted 7:30a.m. December 7, 2016. A new General Bulletin will be issued when conditions warrant.

Helon Hoffer/Frank Carus
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2016-12-07