Avalanche Advisory for December 27, 2013

This advisory expires today at midnight.

Tuckerman Ravine has Considerable and Moderate  avalanche danger.   Sluice, Lip, Center Bowl, Chute, Left Gully, and Hillman’s Highway have Considerable avalanche danger today. Natural avalanches are possible and human triggered avalanches are likely. Lobster Claw, Right Gully, Lower Snowfields and Little Headwall have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.

Huntington Ravine has Considerable and Moderate avalanche danger.  Central, Pinnacle, Odell, South and Escape Hatch have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Dangerous avalanches conditions exist. North, Damnation and Yale  have Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible.

AVALANCHE PROBLEM:  Storm snow yesterday and today will be part of our problem today along with wind slab developing later in the day as wind speeds increase. 7+” of light density snow fell in the higher terrain yesterday which has formed touchy and reactive storm slabs. This snow will be overlaid with denser  wind slab today creating a dangerous mix of reactive slabs, which will gain thickness, mass and potential energy as the day continues, to negotiate. Poor bonding surfaces in the form of cold ice and rock features as well as a relatively thin snowpack over rocky, bushy terrain are all widespread issues in both ravines. Thinly covered rocks and unburied terrain traps increase the hazard of any sliding fall or avalanche. These problems are likely to continue through the weekend.

WEATHER:  Snowfall yesterday exceeded expectations ending with almost double forecasted amounts.  Consistent rates of s1 to s2 produced 6.6” (17cm) on the summit as of midnight.  Light snow has continued since then and is expected through the day.  Overall, by the time the upslope precipitation ends, we should have a total event accumulation between 8.5” (21.5cm) and 10.5” (26.5cm).  Snow density has been between 6-7% and we expect this trend to continue with the low temperatures firmly in place.  At the onset of Thursday’s precipitation, winds were from the S and SW where they remained before transitioning to the West late in the afternoon.  Generally, wind velocity remained between 35mph (56kph) and 50mph (80kph) before picking up after dark.  Winds from the W are expected to gain strength today gusting over 70mph (112kph) this afternoon and building towards 90mph during the overnight and into Saturday morning.  This will continue loading new snow today and tonight.

SNOWPACK: Yesterday’s snowfall began cold and dry, likely bonding poorly to the icy surfaces left behind by the recent ice storm and rain.  It is plausible that we endured a number of smaller natural avalanches and dry loose sluffs late in the day due to the moderate winds, low density snow, and slick bed surfaces.  Winds shifted from the SSW late in the day and have loaded predominately E facing slopes overnight which will continue through today.  The wind history over the past 24 hours has therefore loaded the start zones from N facing through E and SE aspects.  It is likely that building winds will break apart crystals at an increasing rate and pack them into denser slabs over yesterday’s low density slabs creating an unstable scenario.  We would anticipate unstable slabs on the majority of the existing snowfields, however small, in both ravines.  Due to the wide distribution of instabilities of Storm Slabs and Wind Slabs even the skilled and experienced user will find it difficult to avoid potential natural avalanches or being a trigger due to the touchy nature of the cold low density snow.  Stability test results may be variable, but should give you a consistent message-poor stability.

In addition to avalanche problems the following hazards should be factored into your travel plan.

Generally icy trail conditions still exist. We highly recommend crampons and an ice axe for travel in steep terrain and other traction footwear for travel on low elevation hiking trails.  New snow will hide slick sections as well as rocks and holes between rocks.  Recent new light density snow will amount to less than 6″ from Hermit Lake down the Sherburne and will  hide rocks, water ice and death cookies of refrozen crust. Sherburne ski trail coverage is very thin.

Long sliding falls. In those locations where continuous snow coverage exists, the icy surface beneath light density snow will make it difficult for you to stop yourself if you fall. The thin layer of new, low density snow will make assessing the traction of each step challenging.

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 0823 a.m. 12-27-2013. A new advisory will be issued tomorrow.

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

2013-12-27 Print friendly