Avalanche Advisory for Sunday, December 24, 2017

Huntington and Tuckerman Ravines have MODERATE avalanche danger. All forecast areas have Moderate avalanche danger. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully to identify features of concern. Lower Snowfields and Little Headwall in Tuckerman are the exception with Low avalanche danger due to lack of a developed snowpack. Natural and human triggered avalanches are unlikely there.

 AVALANCHE PROBLEM: Previously existing wind slab and sluff piles beneath steep features were encased in ice yesterday afternoon. A brief visit to Hillman’s this morning in low visibility conditions revealed that you could find, and posthole into, areas of soft, dry snow beneath a glaze of ice in lots of areas. One of the concerns that would be on my radar today would be some of the large piles of sluff sitting beneath funnel points in our steepest terrain. An outside chance of perforated the ice and being the trigger on one of these wind slab/sluff piles would be enough to keep me from traveling alone or leaving my beacon, probe and shovel in the car. Additionally, light snow fall continues this morning and may build small wind slabs in lee areas.

 WEATHER: It should be no secret that we saw a mixed bag of precipitation yesterday. At Hermit Lake, around 5” of snow fell before the storm switched over a crust building rain and frozen precipitation mix in the afternoon. Temperatures hovered just below freezing with southerly wind around 40 mph through the bulk of this storm. Precipitation tapered off overnight, summit temperature dipped to the current single digits above zero F, and wind shifted through W to NW increasing to the current 70 mph. Today’s break between storms should be accompanied by temperatures in the teens, mostly cloudy skies, and a wind that will eventually decrease as it shifts through W and S to SE as snowfall begins tonight. A significant storm in the next 36 hours looks to bring a storm total of around a foot of new snow on southerly wind that will shift NW and elevate as snowfall tapers off. It certainly looks like a white Christmas!

SNOWPACK: A breakable freezing rain crust of 1-2 cm thickness is our primary surface from the lower mountain up to the floor of the ravines. We believe that this crust is pervasive through our upper terrain, though visibility limits our current ability to confirm this. Beneath this crust formed yesterday afternoon much of our terrain will hold the comparatively dry snow that fell prior to crust formation. This snow will vary in thickness from several inches to more than a foot. Though you would be hard pressed to trigger an avalanche today in this snow it will likely be a player in tomorrow’s avalanches. The significant snow and wind coming Monday could produce avalanches on this crust that would ultimately break it apart and entrain the soft snow below.

The Lion Head Winter Route is open and the preferred route to the summit from the east side. Daylight hours are short today…don’t forget to adjust your turn around time and headlamp. Expect to posthole into soft snow beneath the crust if travelling off the beaten path.

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 8:00 a.m., Sunday, December 24, 2017. A new Advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2017-12-24