Avalanche Advisory for Friday, December 22, 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. Heightened avalanche conditions will exist on specific terrain features. Evaluate snow and terrain carefully. North, Damnation and Yale Gullies have Low avalanche danger. Natural and human-triggered avalanches are unlikely.

Tuckerman Ravine has Moderate and Low avalanche danger. Sluice, Lip, Center Bowl, Chute, Left Gully and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions will exist on specific terrain features. Evaluate snow and terrain carefully. Lobster Claw, Right Gully, Lower Snowfields and Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: New wind slabs are the primary avalanche problem today. 3-5” of new snow will likely be blown into relatively thin but potentially reactive wind slabs in areas lee of a light southeast wind. Additionally, anticipate dry loose avalanches or sluffing from steep terrain. This will build piles of sluff debris which behave as a wind slab. Both of these problems will develop later in the day. The size and ease of triggering of these avalanches is highly dependent on localized wind speed and direction. Summit wind speeds are generally much higher than those in our start zones so assess conditions carefully through the day. The likelihood and size of a natural or human-triggered avalanche will increase through the day and push the avalanche danger up, especially after dark as snow continues.

WEATHER: Light snowfall has begun on the summit this morning. Snowfall will begin at lower elevations as the cold, dry air in place begins to saturate. The current temperature on the summit is 6F with a light west wind at 22 mph. Temperatures will rise to the lower teens F as winds shift to the southwest by nightfall. Expect 3-5” of new snow by the end of the day. Visibility will be reduced as summit fog builds through the day.

SNOWPACK: Successive Canadian clippers this week delivered 19” of snow (2.23” water) to the higher terrain since Sunday. Thursday, signs of natural avalanches were observed in Hillman’s, Pinnacle, Odell and possibly high in the exit of Damnation. These areas likely slid Wednesday. Field work yesterday in Tuckerman showed that this snow was hammered by wind on Wednesday and early Thursday. The currently firm and heavily textured surface snow should form a reasonably good bonding interface for new snow today in all but the steepest areas. As noted above, expect avalanche danger to rise through the night and anticipate elevated danger tomorrow as snow continues and then turns wetter as temperatures warm. Wet snow or sleet will likely overload the new dry snow during the day tomorrow.

Due to this week’s snow filling things in and expanding the start zone on the Lion Head Summer trail, the Lion Head Winter Route is open and the preferred route to the summit from the east side. The John Sherburne Ski Trail will be great skiing today but there are still rocks in the usual wind scoured areas that will be barely submerged by new snow. Daylight hours are short today…don’t forget to adjust your turn around time!

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., Friday, December 22, 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

2017-12-22