Avalanche Advisory for Friday, March 24, 2017

This advisory expires at Midnight.

Huntington Ravine will have CONSIDERABLE and MODERATE avalanche danger. Central, Pinnacle and Odell Gully will have Considerable avalanche danger. Natural avalanches will become possible and human-triggered avalanches will be likely. All other forecast areas have Moderate avalanche danger. Natural avalanches will be unlikely and human-triggered avalanches will be possible.

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. Sluice, Lip, Center Bowl and Chute will have Considerable avalanche danger. Natural avalanches will become possible and human-triggered avalanches will be likely. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches possible.

 AVALANCHE PROBLEM: We are starting out the day with human triggered avalanches being possible only in the steepest portions of Sluice, Lip and Center Bowl, and possibly Central Gully in Huntington, with human-triggered avalanches being unlikely in all other forecast areas due to the strength or lack of continuity of existing wind slabs. East facing forecast areas, particularly upper start zones, will be in the bullseye for developing these wind slabs this afternoon while other aspects will become crossloaded. New snow on increasing west winds will add a bit of stress to existing wind slabs, but the primary problem will be within the new snow. Increasing temperatures and increasing wind speeds will set the stage for increasingly dense slabs over soft new snow falling later this morning. As the day wears on, small to medium sized natural avalanches will become possible in considerable rated terrain. Moderate rated terrain could generate smaller human triggered avalanches and even some small, loose dry natural avalanches in the steepest areas. Reduced visibility and increasing hazard will make conservative terrain choices a good idea today.

 WEATHER: The wind and cold of the past few days abated a bit overnight. Wind has slackened to the 20-30 mph range and shifted to blow from a generally WSW direction. Summit temperature is currently 9 degrees F and is expected to rise to the mid-20’s. Today, a system bearing moisture will move in from the west bringing 1-3 inches of snow this afternoon and evening to Mt. Washington. The NWS has forecast a maximum snow water equivalent of .24” with this storm but available low level moisture and upslope enhancement may bring up to 5”. Westerly wind will increase through the afternoon to approximately 45 mph with gusts in the fifties.

SNOWPACK: Stubborn, firm wind slabs that are thick and well developed in the Sluice, Lip, and other more isolated pockets remain our primary concern this morning, but the coming snow this afternoon will alter these conditions. Wind-textured and similarly firm “sastrugi” snow can be found in much of Chute and Hillman’s as well as South and Escape Hatch. The weeks-old rain crust surface has been largely covered by wind deposits over the past few days, but it still exists as a stable travel option in much of Left Gully and to a lesser extent in other areas.  Additionally, south facing aspects that have been wind scoured following the melt-freeze cycle early this week offer similarly firm, stable snow. The areas below Right Gully and Lobster Claw display this thick melt-freeze surface layer. However, the arrival of snowfall and moderate wind later today should create relatively soft and potentially sensitive new wind slab.  Snow totals will dictate the hazard associated with this new layer. Remember, 2 inches of snow above Tuckerman can easily load Sluice, Lip, Center Bowl and Chute with a much thicker 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 Harvard Cabin.

Posted 8:12 a.m., Friday, March 24, 2017. A new advisory will be issued tomorrow.

Frank Carus/Ryan Matz, Snow Rangers
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856