This advisory expires at Midnight.
Huntington Ravine will have CONSIDERABLE, MODERATE, and LOW avalanche danger. Central Gully has Considerable avalanche danger. Travel in avalanche terrain is not recommended. Yale, Pinnacle, Odell, South, and Escape Hatch have Moderate avalanche danger. Evaluate snow and terrain carefully. North and Damnation have Low avalanche danger. Watch for unstable snow on isolated terrain features.
Tuckerman Ravine will have CONSIDERABLE, MODERATE, and LOW avalanche danger. Sluice, Center Bowl and Chute have Considerable avalanche danger. Travel in avalanche terrain is not recommended. The Lip, Left Gully, Hillman’s Highway, and Lower Snowfields have Moderate avalanche danger. Evaluate snow and terrain carefully. Lobster Claw, Right Gully, and the Little Headwall have Low avalanche danger. Watch for unstable snow on isolated terrain features.
AVALANCHE PROBLEM: Today’s avalanche problem is wind slab. This developed Wednesday night into Thursday and has naturally released in a few steep, wind loaded areas. Continued cold weather today will not improve stability. Areas of the greatest concern are larger wind loading slopes in the lee of W and WNW wind, such as Central Gully, the Sluice and Chute, places that received significant loading but have not avalanched. Avalanche activity yesterday below the ice in the Lip to the Center Bowl and the area beneath Harvard Bulge and Yale failed on the interface between old wind slab or ice crust and the new snow. This natural activity should serve as a red flag for areas that still contain areas of wind slab and no signs of avalanche activity. Evaluate snow carefully before you commit to a slope.
WEATHER: A total of 10” of snow arrived over the past 48 hours. This snow began to fall on relatively light southerly winds and ended as the wind shifted to the NW and increased to 80mph. Currently, it is -8.5F on the summit with a W wind of 38 mph. Today, the temperature should remain below zero for the day and begin to rise as darkness sets in. Wind will shift to the SW and increase to 60mph before decreasing late in the day. Clouds will linger with periods of clearing, possibly delivering up to an inch of snow in the afternoon.
SNOWPACK: Wind slab that formed Wednesday night into Thursday is the dominant snow surface in avalanche terrain. The bottom of this layer is soft (fist hardness) snow and then increases in hardness to finger to pencil hard at the surface. Northwest winds of 70 mph Thursday morning left mostly firm old snow in the northern gullies of both ravines that will provide good climbing. Areas in the lee of W and WNW winds, such as Central Gully, and Sluice through Chute saw more significant loading, leaving a smooth or pillowed surface in places that did not avalanche. Routes like Yale and Hillman’s, while not receiving the most loading, contain areas of wind slab that will need to be carefully negotiated. Natural activity occurred yesterday, notably in the Fan of Huntington below Harvard Bulge and across the Lip and Center Bowl of Tuckerman. These failures occurred at the interface of the wind slab and old snow. The large avalanche in Tuckerman did step down into old snow, leaving the melt/freeze crust from mid-January exposed in places lower in the Bowl and in the Lip.
• 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 8:30 a.m., Friday, February 9, 2018. A new advisory will be issued tomorrow.
Helon Hoffer, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856