Avalanche Advisory for Sunday, December 17, 2017

This advisory expires at Midnight.

Huntington Ravine has MODERATE and LOW avalanche danger. Central, Pinnacle, and Odell Gullies have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Evaluate snow and terrain carefully. North, Damnation, Yale, South and Escape Hatch have Low avalanche danger. Natural and human-triggered avalanches are unlikely.

Tuckerman Ravine has MODERATE and LOW avalanche danger. The 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.

AVALANCHE PROBLEM: Despite 3” (6.9 cm) of new snow at Hermit Lake yesterday afternoon, our wind slab avalanche problem is manageable with careful assessment and cautious travel. Moderate rated areas likely contain more softer slabs that may be susceptible to human-triggering but also contain enough areas of firm snow to provide for safer travel options. Remember that the scattered slabs that exist can still knock you off your feet and push you around so consider the consequences when micro route-finding. Low rated areas contain a mix firm, chalky slabs and heavily textured sastrugi. 

WEATHER: A series of Canadian clippers is affecting our weather for a while, separated by brief spells of clearing as high pressure tries to take control. Yesterday’s clipper brought steady moderate snowfall for a couple of hours in the afternoon along with lighter snowfall for most of the day. Winds out of the west-northwest during the period of moderate snow shifted to the NNW overnight. Though only reaching to the 60 mph range for a brief period, this fluffy snow was scoured out of the terrain more than deposited in any significant quantity from the Alpine Garden. NNW are continuing to blow some snow around but there isn’t a whole lot of snow left to be moved and certainly not with the diminishing wind speeds forecast for today. Overall, a nice chilly day at higher elevations, with temps climbing to 7F from the current -6F.

SNOWPACK: Ryan and Sarah dug pits in the Left Gully and Chute areas. Their findings match up with other observations that the firm slabs built on the Tuesday/Wednesday storm are pretty well glued to the older bed surface. Moderate to hard shears coupled with solid bridging power in that slab lower our concern for triggering something larger in that slab. That generally leaves us with the more recent wind slabs that have developed since the 16” storm on Tuesday. These slabs are the more triggerable, but are widely scattered in the terrain and not very thick. Be sure to poke and probe the snow as you move around to know which type of slab you are dealing with. The weather this week brings more clippers and more snow. These light snowfalls can bring really variable avalanche danger depending on wind speed, direction, snow density and other factors. Be sure to check the weather and this advisory as you formulate your plans.

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. The John Sherburne Ski Trail has improved but there are still rocks barely submerged by new snow and wind scoured bare areas. Solid skiers were walking parts of the trail yesterday.

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 8:17 a.m., Sunday, December 17, 2017. 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

2017-12-17