Avalanche Advisory for Wednesday, January 3, 2018

All forecast areas in Huntington Ravine have LOW avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

Tuckerman Ravine has MODERATE and LOW avalanche danger. Lip, Center Bowl, and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully. All other forecast areas have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: Firm and generally stubborn wind slabs are the primary avalanche problem today. These firm slabs have good bridging strength in lots of areas but realize that thin spots, convexities and other trigger points may still be lurking.  Evaluate snow and terrain carefully as you move around the terrain today. You’ll find mostly firm and fairly smooth slabs in terrain that hasn’t seen the scouring or sastrugi building action of the wind. Low rated areas have fewer areas of concern and provide more terrain opportunities to avoid potentially unstable firm wind slabs.

WEATHER: A tenth of an inch of snow fell yesterday after a cloud cap and summit fog enveloped the high peaks in the afternoon. Summit temperatures have risen to a balmy -6F this morning following the protracted arctic cold spell. Today looks like the nicest day to get into our terrain with a high of 3F, clearing skies and westerly winds in the 25-35 mph range. The real weather story lies in the approaching low pressure system. The track of the storm changes with each model cycle but generally closer to shore. It is safe to say that we will see avalanche danger rising, with storm slabs building, through tomorrow with peak natural wind slab avalanche activity likely to occur Thursday evening. Westerly winds will build additional wind slabs Friday but to what extent depends on the amount of total available snow.

SNOWPACK: A mix of surfaces is waiting to receive the new snow, with rough rimed ice crust in some upper start zones, heavily textured sastrugi lower and large smooth wind slabs and sluff piles mid-slope. Minor wind loading has continued off and on through the past several days despite little or no new snow over that time. Between the frigid temperatures and less than ideal skiing conditions in steep terrain, only a few areas of our wind hammered slopes were tested. The slopes that were tested by foot traffic such as the Lip, Sluice and Left did not avalanche in spite of the minor faceting that occurred in our mid-upper snowpack. This is attributable to the strong bridging power and propagation resistance of these firm slabs, the spatially variable bonding surfaces and to some degree, the abundance of anchors still unburied. Given the overall good stability, today would be a reasonable day to move around in most of our terrain using safe travel practices.

The Lion Head Winter Route is the safer route to the summit on the east side. Both the Tuckerman and Huntington Ravine Trails pass through several avalanche paths and are challenging mountaineering routes with significant hazards.

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 Harvard Cabin.
• Posted 7:42 a.m., Wednesday, January 3, 2018. A new advisory will be issued tomorrow.

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

2018-1-3