This advisory expires at 12:00 midnight, January 22, 2013
Tuckerman Ravine has Considerable and Moderate avalanche danger. The Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Right Gully, Left Gully, and Hillmans Highway have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Lobster Claw, the Lower Snowfields, and Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely.
Huntington Ravine has Moderate and Low avalanche danger. Central, Pinnacle, Odell, and South gullies have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. All other areas have Low avalanche danger. Natural avalanches are unlikely except in isolated terrain features.
Avalanche danger will be increasing through the day. Many areas currently have lower danger than forecasted but will increase in danger as the day wears on.
Yesterday, clear but cold and moderately windy conditions allowed us to travel safely into Tuckerman Ravine to assess our snowpack. What we found, coupled with new snow blown into the Ravines today, is the focus of avalanche concerns today. The windslabs we found yesterday were shearing cleanly and left a strong impression that steep terrain held slabs that would be sensitive to a human trigger. The paltry (1” or 2.5cm) snowfall last night from the low pressure system off the Maine coast was in the 5% density range and will exacerbate our instabilities as it builds into new slabs on slowly increasing winds. Starting at 8pm last night, summit winds out of the SW wrapped to the W and blew in the 15-20 mph (25-30kph) range. Winds are forecasted to gradually increase and shift to the NW this afternoon to 50mph (80kph) at sunset. The increasing wind speed will pack snow on top of the weak, lower density layer that was deposited through the night and morning hours. Expect to find unstable pockets of snow near the top and in the midsection choke points of South, Odell, Pinnacle and Central and to a lesser extent in mid-section chokepoints of Yale and Damnation. Look for larger areas of triggerable slabs, which may even slide naturally later in the day, in the Chute, Center Bowl, Lip and Sluice.
Smooth continuous bed surfaces, which have slowly increased in size since our recent January thaw, exist in some areas of the ravines. Lots of melting, particularly in our south facing terrain, decimated our snowpack and created the hard icy surfaces scattered around in wind scoured locations. These old surface are camouflaged by newer snow and makes worse another hazard that frequently threatens skiers and climbers…the long, sliding fall. Wind deposited snow often forms lens shaped pockets of snow that are thin at the edges. While you may be able to boot up the thicker, center of these pockets with plenty of boot penetration, you’ll find the edges of the slabs may break out from under foot, or ski, sending you skidding down the slope. Remember that these thinner edges can also serve as the weak spot and point at which cracks develop and sometimes propagate into the rest of the slab. Windblown snow is also hiding undermined areas of snow and ice from the recent thaw as well as newly formed ice so crampons will likely be needed sooner and on lower angled terrain than you might think.
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 9:00am, January 22, 2013. 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