Avalanche Advisory for Monday December 29, 2014

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. The Sluice, Lip, Center Bowl, Chute, Left Gully, and Hillman’s have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Careful snowpack and weather evaluation, cautious route-finding, and conservative decision making are essential.  All other forecast areas have Moderate avalanche hazard. Natural avalanches are unlikely and human-triggered avalanches are possible. Evaluate snow, weather, and terrain carefully.

Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger. North, Damnation, Yale, Central, Pinnacle, and Odell have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Careful snowpack and weather evaluation, cautious route-finding, and conservative decision making are essential. South Gully and the Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow, weather, and terrain carefully.

AVALANCHE PROBLEM: We have the potential for additional snowfall and strong consistent winds leading to the development of wind slab in lee areas. Winds today will remain quite strong, which should allow loading to continue throughout the day. This wind loading and subsequent slab development will keep the snowpack trending toward worse stability.

WEATHER: Since the thaw ended and snow began to fall, Mt. Washington Observatory has recorded 5.1″ (12.5cm) of roughly 11% density snow with winds holding strong from the W and NW. Due to temperature differences, elevations below Hermit Lake received wet snow and rain instead of the snow that landed in the alpine zone. After the bulk of the snow fell, there was a modest lull yesterday afternoon before winds cranked up again to 60-80mph (95-130kph). This morning the strong W and NW winds will continue and there are some snow squalls expected. This may bring another 1-3″ (2.5-7.5cm) of snow to upper elevations.

SNOWPACK: We are still in recovery mode from the Christmas rain event. If we had a full mid-winter snowpack, 5″ of new snow with another 1-3″ on the way, coupled with these winds, would make for pretty simple forecasting and hazard assessment. It would scream “Danger! Danger!” with red lights flashing — or at least that’s how it would look to me. In the current situation, we have a more discontinuous snowpack and smaller bed surfaces. Avalanche tracks and runout paths are less developed. Many locations have numerous anchors still well exposed. The alpine zone in not fully encased in snow, so there are lots of locations for snow to get “trapped” instead of  blown into the ravines. All these factors do contribute to the nature of the avalanche potential being such that we expect relatively smaller sized avalanches and the likelihood of a naturally triggered avalanche falling somewhere on the line between Moderate and Considerable (i.e. unlikely vs. possible.) The primary factors that tipped the scale toward the Considerable ratings include the total amount of snow available for wind loading and the ability of the winds to move large quantities of snow in to the ravines. This data is difficult to ignore. Other factors come into play, such as the lull in winds and slight shifts in direction leading to variations and potential weak interfaces within the new slab. We believe that a savvy traveler who is very observant might be able to thread the needle through the terrain today, but it would not be without risk and uncertainty. If you intentionally seek to find softer snow, you won’t be threading the needle, you’d be sticking yourself right in the thumb with it, as you will be seeking the areas with the same new slab we are concerned about today. With a little luck, visibility will improve late today and more visual clues will help with decision making. Unless this happens, keep in mind that 8″ can translate to a lot of wind slab!

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 8:00 a.m. December 29, 2014. A new advisory will be issued tomorrow.

Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2014-12-29