Avalanche Advisory for Saturday, February 28, 2015

This advisory will expire tonight at 12:00 Midnight.

Tuckerman Ravine has Moderate and Low avalanche danger. Sluice, Lip, Center Bowl, and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully. Lobster Claw, Right Gully, Left Gully, Hillman’s Highway, the Lower Snowfields, and Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features.

All forecast areas of Huntington Ravine have Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features. Recent very cold air in place has stressed some of the ice features and has caused recent ice dam ruptures.

AVALANCHE PROBLEM: The primary avalanche threat today is Persistent Slab. Triggering one of several weak layers in the snowpack requires finding just the right thin spot in the slab. These slabs are generally of the firm (1F-P) variety but, in some areas, they have a weak layer of snow located either between layers or deeper in the snowpack, near a buried crust. Moderate rated areas have the greatest potential for what would be a large, hard slab avalanche. A distant second threat is from Wind Slabs which have formed at various times this week. Though pockety and not reactive in nature, a small slab on steep or challenging terrain could surprise you.

WEATHER: It looks like another cold, crisp bluebird day on tap for today. A high temperature around 0F (-18C) with a NW wind shifting to the W at 25-40 mph (40-65 km/h) on the summit will remind you of the value of hoods, balaklavas and face masks. Gusts to 50 mph (80 km/h) will drive this point home. The next chance for snow appears to be tomorrow (Sunday) night as a frontal system approaches.

SNOWPACK: Howling winds on Monday dumped quite a bit of snow into Tuckerman Ravine but scoured out most of Huntington. Low rated areas of both Ravines predominately received scouring in some places down to a rock hard old surface. Though areas of the aforementioned persistent slab certainly exist in Low rated areas, there are more opportunities to avoid them by staying on the older, harder surface or by otherwise reducing your exposure with cautious travel techniques. The persistent slabs that are the main concern on our radar right now and though tough, they can fail, propagate a crack and generate a destructive avalanche. Chris’s pit beneath the Chute demonstrated this tendency with ECTP 8, 9 and 10. There are at least two faceted layers holding our attention right now. You could find early facets in the soft snow interface between the slabs that most likely developed during wind loading on Saturday and Monday. You are also likely to find deeper and much more advanced facets around a couple of buried crusts. In the bowl beneath Sluice this facet layer was failing 90-95cm down in the moderate range (CT14, 14, and 19). It is likely that these facets will be most advanced on southerly or westerly aspects where temperature gradients have been the greatest. Bigger slopes present the greatest threat with the least number of safer travel options so carefully consider how much you are willing to expose yourself to this threat in order to recreate on firm snow. Remember that this type of avalanche problem is fairly difficult to trigger requiring a thin spot in the slab, a relatively large dynamic load such as surface wind slab avalanche, a new snow (or water) load or a large increase in temperature.

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 8:50a.m. February 28, 2015. A new advisory will be issued tomorrow.

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