Avalanche Advisory for Friday, December 29, 2017

Huntington Ravine has Moderate and Low avalanche danger. Central, Pinnacle, Odell, South, and Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully, identify features of concern. North, Damnation, and Yale gullies 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. Sluice, Lip, Center Bowl, Chute, Left, and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully, identify features of concern. Lobster Claw, Right Gully, Lower Snowfields, and the Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

 AVALANCHE PROBLEM: Firm and relatively stubborn to trigger wind slabs that exist over much of our terrain are our primary avalanche problem today. Realize that this layer will be easiest to trigger in thinner and/or softer areas, which is difficult to visually discern when route finding. Today remains a low probability, high consequence risk situation for a number of reasons. Bitterly cold weather will complicate any problem and a number of our avalanche paths continue to have nasty runouts. Continue to realistically consider “what if” scenarios in your travel planning.

 WEATHER: It’s cold and will remain so through the forecast period. The summit is currently experiencing a slight respite from negative double digits, with temperatures hovering just above 0F, though the mercury will drop towards the teens below zero through the day. NW wind below 30 mph will push higher this evening, possibly exceeding 50 mph overnight. Increasing clouds should produce snow showers that will bring a trace to 2” of new snow. Tomorrow will bring similar temperatures and NW wind with a lesser chance of snow accumulation.

SNOWPACK: Precipitation and wind over the past week has resulted in further progression of our terrain towards full winter snow cover. Wind loading and the resulting avalanches have contributed significantly towards filling in the lower portions of our avalanche paths. We expect that many of the avalanches in the past week wiped out the 1-2 cm crust which formed last Saturday, though exceptions can likely be found. Where avalanches did not occur, the crust which lies over soft snow (4F-F hardness) still exists under our current firm surface slabs. These current firm and relatively stubborn slabs are our primary avalanche problem today. We do still harbor concern for deeper instability in the form of the soft layer under last Saturday’s crust. If the surface slab was triggered, the possibility remains for an avalanche to step down and entrain significant snow.

The Lion Head Winter Route is open and the preferred route to the summit from the east side.

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 8:00 a.m., Friday, December 29, 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

2017-12-29