Avalanche Advisory for Thursday, February 27, 2014

This advisory expires at Midnight.

Tuckerman Ravine will have CONSIDERABLE and MODERATE avalanche danger. The Sluice, Lip, Center Bowl, Chute, Left Gully, and Hillmans Highway will have Considerable avalanche danger.  Natural avalanches are possible and human triggered avalanches are likely. Conservative decision making and cautious route finding is essential.  Lobster Claw, Right Gully and the Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The Little Headwall has Low avalanche danger. Natural and human triggered avalanches are unlikely.

Huntington Ravine will have CONSIDERABLE and MODERATE avalanche danger. Central, Pinnacle, Odell, and South Gully have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Conservative decision making and cautious route finding is essential.   All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.

AVALANCHE PROBLEMS: Wind slabs will again be the primary hazard today. Southwest winds will load forecast areas which have a primarily northeasterly aspect today. The degree to which these slopes are loaded depends on the timing of the increase in wind speed and the rate of snow fall in the afternoon. Today’s new wind slab is adding mass to existing wind slabs that developed over the past 3 days. These older wind slabs are a close second in terms of our hazards. These slabs are resting on an icy crust layer and is capable of cracking and producing an avalanche. Persistent slabs should also be on you radar when approaching areas that receive alot of loading from sluff activity, basically where slope angles transition from steep to less steep and allow snow to pile up into deep hard slabs. Cold temperatures and low density snow can be easily transported by today’s forecast windspeed.

WEATHER: Approximately 4.5″ (11.5cm) of snow have fallen on the summit of Mount Washington in the past 3 days as a low pressure continues to spawn squall lines across the range. A trace to 2″ today on southwest winds at 30 mph or so will move new snow and crossload terrain features. Ground level clouds and blowing snow will flatten the light and make snow surfaces more difficult to see and assess. Travelling outside of avalanche terrain, the primary challenge will be the cold temperatures hovering around zero, depending on elevation, as well as a breakable ice crust over softer snow in the woods.

SNOWPACK: Rain crust formed during the mixed precipitation that fell on the 20th is still a big player in our snowpack. Subsequent wind slabs and sluff piles were deposited on this layer which is also potentially generating facet growth. While this ice crust is over hard snow in areas which were previously scoured out by wind such as the lower 2/3’s of Hillman and Left, it is over much softer layers of cold snow in others. If I were out today looking for interesting snowpack features, faceting among the ice pellets below the ice crust as well as just above the crust would be the subject of my curiosity. As mentioned several times in the past week, the ice crust is contributing to the tensile strength of the weaker snow beneath. This strength may be overcome by the increased loading that has occurred during the past several days. Avalanches that occur could step down through the ice crust and entrain more snow than just the surface layers of windslab that grow today. An avalanche occuring in the hard slabs formed by sluffing activity can always be larger than you might expect so consider your options when travelling in these areas.

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 Visitor Center, or the caretakers at Hermit Lake Shelters and Harvard Cabin. Posted 8:30a.m. 2-27-2014. 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

2014-02-27 Print friendly