Avalanche Advisory for Tuesday, December 19, 2017

This advisory expires at Midnight.

Huntington and Tuckerman Ravines have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. The only exception to this rating is the Little Headwall, which still lacks significant snowpack development. It is rated Low for the possibility of small avalanches in isolated terrain.

 AVALANCHE PROBLEM: Newly formed Wind Slab that will be soft and reactive to a human trigger this morning is our primary avalanche problem. New snow in the past 24 hours on a consistent W wind has and is still loading our terrain. Continued and increasing wind through the day has the capacity to further decrease stability. We expect areas not yet reaching today’s Considerable danger rating to reach Considerable later today. Areas experiencing the greatest loading could surpass this rating by the time this advisory expires at midnight.

 WEATHER: The summit and much of our terrain has received at least 5” of snow in the past 24 hours on a consistently W wind hovering near 50 mph. We are currently seeing a brief lull in precipitation before snowfall begins again on increasing W wind that should shift NNW and gust to around 100 mph by tomorrow morning. Temperatures will remain at least a few degrees below freezing. Forecast snowfall totals are mixed, so we’re expecting new snow in the 3-10” range in the coming 24 hours.

SNOWPACK: This morning’s relatively soft wind slab problem will be most pronounced on aspects lee to a W wind, where a thinner slab formed Sunday into Monday exists that is similar in density. Wind transport continues currently. Remember that wind deposits can easily quadruple actual snowfall totals, or more. We expect this layer to be quite reactive to a human trigger. Natural avalanches are possible as wind ramps up through the day, and by tomorrow morning we’ll likely see these new slabs largely eroded and/or hardened by this wind. Beneath these softer surface slabs, our more developed paths hold firm (1F+) snow that is not likely to pose a stability concern. Less developed paths will hold a mix of hard and soft snow, rocks, ice, and vegetation beneath the recent deposits. With many hazards exposed or thinly veiled, realize that the consequences of capture by an avalanche remain in an elevated early season state.

The summer Lion Head Trail is the safer route to the summit than trails through Tuckerman and Huntington. The Lion Head Winter Route will open when snow fills in avalanche paths on the summer trail and fills in the winter route enough to cover rocks, mud and bushes. Coverage on the John Sherburne Ski Trail continues to improve but there are still rocks barely submerged by new snow. We love to ski, and we haven’t yet skied it.

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 8:20 a.m., Tuesday, December 19, 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