Avalanche Advisory for Monday, February 8, 2016

Tuckerman Ravine has MODERATE and LOW avalanche danger.  Center Bowl and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Evaluate snow and terrain carefully to identify features of concern.  Right Gully, Sluice, Lip, Left Gully and Hillman’s Highway have Low avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features. Lobster Claw, Lower Snowfields, and the Little Headwall are not posted due to lack of snow cover.

Huntington Ravine has MODERATE and LOW avalanche danger. Central Gully has Moderate avalanche danger.  Natural avalanches are unlikely and human-triggered avalanches are possible. Pinnacle, Odell and South have Low avalanche danger. Natural and human-triggered avalanches are unlikely. North, Damnation, Yale, and the Escape Hatch are not posted due to lack of snow cover. Exercise caution in these areas and expect the potential for isolated patches of instability.

AVALANCHE PROBLEM: Wind slab is the primary avalanche problem today. WSW winds the day before yesterday built wind slabs in wind sheltered, lee areas. These wind slabs were not particularly touchy, thick or widespread but still deserve caution. Moderate rated areas have the largest expanses of these wind slabs with low rated areas having similar slabs but to a more limited extent. Late in the day, new snow will reduce visibility and obscure surface snow, making it more challenging to stay on the older, more stable snow. Expect new snow starting this afternoon to lead to elevated avalanche danger overnight and into tomorrow.

WEATHER: Temperatures were in the upper teens F overnight with very light easterly winds. Cold northern air will move in and drop temperatures to the single digits F (5F/-15C) this afternoon with wind speeds rising to the 25-40mph range on the summit. A low pressure system passing well off shore will send snow showers our way this afternoon with bands of precipitation producing heavier snow after dark. Expect anywhere from 4 to 9” of new snow by tomorrow with more snow showers to follow through the day. Another low pressure system could produce more snow on Tuesday.

 SNOWPACK:  The old surface snow in the Ravines is the melt-freeze crust formed from the warm spell this past Wednesday and Thursday.  We found the crust to be 25cm thick and knife (K) hard.  Snow that fell on Friday, Saturday, and Sunday, about 3.3″, lies on top of this.  We found this newer snow forming a one-finger (1F) hard wind slab that varied greatly in depth, from close to 30cm thick to non-existent less than 5m away.  Shear quality was resistant but smooth (Q2) within the wind slab.  This slab began to form on lighter winds from the W and WNW on Friday, providing the weak layer for the slab that formed later on Friday through Sunday.  This wind slab is discontinuous in many areas like Left and Right Gully in Tuckerman as well as the Sluice and Lip.  The Chute and Center Bowl have the largest areas of this wind slab.  In Huntington, Central Gully has the most developed snowfield and also received the greatest amount of snow compared to the rest of the routes in Huntington.  Areas below the ice bulges of Pinnacle, Odell, and South will also likely harbor this wind slab, although these areas tend to offer easier alternatives to avoid instability.

An injury requiring litter evacuation occurred in Huntington Ravine yesterday due to a long sliding fall on the hard, old surface snow. Use caution, and a belay when necessary, on steep terrain. Self-arrest is not a substitute for a belay rope, particularly in hard snow conditions. The John Sherburne Ski Trail is passable, but just barely, with water ice being the dominant sliding surface. Expect very challenging, dust on crust, conditions later today.

Please Remember:

· Safe travel in avalanche terrain requires training and experience. This advisory 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 7:55a.m. February 8, 2016. A new advisory will be issued tomorrow.

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

2016-02-08