Avalanche Advisory for Monday, February 23, 2015

This advisory expires tonight at 12:00 midnight.

All forecast areas of Tuckerman Ravine have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. The only exception to this is the Little Headwall, which has Low avalanche danger. Natural and human triggered avalanches are unlikely.

Huntington Ravine has Considerable and Moderate avalanche danger. North, Damnation, Yale, Central, and Pinnacle gullies have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Odell, South, and Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.

AVALANCHE PROBLEM: Our avalanche concerns today are focused on recently developed wind slabs as strong winds mix and redistribute a small amount of new snow with previously existing snow sitting above treeline. This will create new slab instabilities throughout most of our forecast areas; however, the most significant loading and hazard is centered in the vicinity of the Sluice, Lip, and Center Bowl. In addition to new wind slabs, there is an increasingly complex snowpack around the ravines (particularly Tuckerman) that may allow for avalanches to step down into older layers, creating larger more damaging slides.

WEATHER: The big story for weather today is the falling temperatures and increasing wind speeds. This will make travel in alpine areas very inhospitable. Read the full summits weather forecast, plan and pack accordingly, and make conservative decisions today. As for avalanche related weather, we have received about 1” of snow early this morning. Winds have already risen to their forecasted speeds of 60-80mph with higher gusts. In our field observations yesterday, we found ample snow on the summit cone on E and NE aspects that will be blown around on these winds, making visibility poor and contributing to stability problems.

SNOWPACK: The number one thing you’ll want to be thinking about is the new snow loading taking place today, creating potential for naturally triggered avalanches and increasing the likelihood of human triggered slides. Prior to this, there was a wide range of conditions in Tuckerman. Right Gully had been cleaned out of the 20” of snow that fell over the last week, leaving firm but skiable conditions for several people to enjoy yesterday. The SW winds are to blame, but they also loaded and cross-loaded other slopes such as the Center Bowl, Chute, and Left Gully. In these areas you can expect to find a mix of hard and soft layers sitting on top of the very hard slab formed on 2/16. The potential exists for this hard slab layer to be triggered if the load is great enough (e.g. an avalanche runs over it). If this happens, you will want to be nowhere near the runout of the Center Bowl in floor of Tuckerman.

Yesterday I observed what I think may have been a long stauchwall on the summit cone, in the same slope as last year’s March 29th close call. I was able to safely get to a small section of crown and found very poor structure in the top 30cm of snow. I have a low degree of confidence that this was anything more than just a small 20’ long avalanche on a rollover, but it may have been a large soft slab avalanche if the whole snowfield slid the way I think it might have. I’m thankful that no one was up there skiing yesterday, because the stability would earn a poor to fair rating on that slope. Remember, just because a slope isn’t forecasted or doesn’t regularly slide does not mean it cannot avalanche.

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 7:45 a.m. February 23, 2015. A new advisory will be issued tomorrow.

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