Avalanche Advisory for Wednesday, March 22, 2017

This advisory expires at Midnight.

Huntington and Tuckerman Ravine have CONSIDERABLE and MODERATE avalanche danger. In Tuckerman, Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Central, Pinnacle, and Odell Gullies in Huntington Ravine have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route-finding, and conservative decision-making are essential. All other forecast areas of both Ravines have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully. The only exception to these ratings is the Little Headwall, which has Low avalanche danger. Natural and human triggered avalanches are unlikely.

AVALANCHE PROBLEM: Wind Slab formed overnight is the primary avalanche problem today. With a currently upside-down, firm over soft nature, this surface layer will be particularly sensitive to a trigger this morning. A lack of visibility hampered morning observations, but we expect this slab to be thick in places and widespread over Chute, Center Bowl, Lip, and Sluice in Tuckerman as well as Central and lower Pinnacle and Odell gullies in Huntington. Pockets in lee areas of west through northwest winds will hold this wind slab in Moderate rated areas. Increasing wind speeds throughout the day will cause this instability to peak this morning or mid-day, decreasing as we approach wind speeds that should scour Huntington and create pockets of very firm slab in Tuckerman

WEATHER: It’s cold and windy up here. The summit is currently recording -2 F, with sustained northwest wind nearing 60 mph and gusts to 70. Throughout the day, this wind will increase, nearing 100 mph, and temperatures dropping to -20F. Snowfall and cloud cover is tapering off as this wind increases and temperature drops, remaining partly cloudy with no precipitation this afternoon.

SNOWPACK: We’re seeing a significant amount of new and blowing snow on the mountain, with 3.5 inches of snowfall recorded at Hermit Lake and 5 inches at the summit in the past 24 hours. Underneath this new snow, a mix of relatively stable surfaces exist. This ranges from pencil to 1 finger hardness wind slab over much of the terrain as well as areas of previously scoured old rain crust. The melt-freeze cycles over the past few days, with current temperatures well below freezing, have facilitated bonding between this wind slab and underlying layers. Snow that fell yesterday and last night arrived on West winds in the mid-40 mph range that shifted this morning to the Northwest and increased, with gusts to 70 mph. This transport of new snow from our largest fetch zones for Tuckerman Ravine has likely deposited a significant amount of snow in the Chute, Center Bowl, Lip, and Sluice. In Huntington, Central Gully should hold the largest wind deposits, both above and below the choke point, with Pinnacle and Odell having quite a bit of similarly deposited snow below the ice.  The wind slab formed in the aforementioned areas will display increasingly upside-down characteristics, with softer deposits made by the light to moderate overnight winds sitting underneath the more dense snow loading under the current winds.  Accordingly, the growing wind slab will be increasingly sensitive to a trigger.  Winds are forecast to increase through the day, with peak summit gusts around 100 mph late today, so we’re likely to see a morning or mid-day peak in instability as this high wind begins to erode the newly formed surface slabs, decreasing their size and sensitivity to a trigger.  Sensitive wind slabs could remain, though, in lower and more sheltered pockets of our considerable rated 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 Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin.

Posted 9:20 a.m., Wednesday, March 22, 2017. A new advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856