This advisory expires at Midnight Wednesday 2-13-2013
Tuckerman and Huntington 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 to identify features of concern.
Over the past couple of days the summit received 5.1” (12.5cm) of new snow on winds coming from the SW to the NW. 1.8” (4.5cm) of this came yesterday on an increasing wind from the W peaking at 96mph (154kph) during the late morning and afternoon. New slabs that have developed recently are a mix of new stellars, graupel, and fragments of redistributed crystals from alpine zones broken up by high W and WNW winds. This mixture was witnessed in Huntington and at Hermit Lake this morning. Currently we still no visibility due to clouds, fog and a bit of blowing snow that has been the mainstay since Monday morning.
Peak instability was likely reached yesterday afternoon during maximum loading due to high winds and new snow. Strong protected lee areas under the Tuckerman Headwall, Lip and Sluice and down low in Huntington’s Central, Pinnacle, Odell and South gullies were areas that likely picked up the most snow being more sheltered from W and WNW winds. If these slabs stayed in place and did not avalanche they are the spots I would expect to be on the upper end of the Moderate danger rating today. Additional slab development today will be quite limited as wind velocities are forecasted to fall down to 20mph (32kph) on the summits. Because of this the vast majority of unstable slabs you will find in the Ravines developed over Monday and Tuesday. In addition to areas of soft and hard slab you will still likely find plenty of old icy surfaces blown clean by high winds from the SW, W and NW. Therefore, be ready to find a high degree of spatial variability on the spectrum from rock hard old surfaces to pockets of soft unstable slabs. Until visibility improves with a dropping wind later today negotiating the best travel route to avoid instabilities will be difficult.
Main points to remember in the field today:1. 3.3” of snow fell on Monday with high SW winds creating some instabilities on aspects with a NE facing component. 2. Since Monday afternoon winds shifted to the W and WNW peaking midday Tuesday with an additional 1.8”of snow. These Tuesday conditions developed new slabs mostly on E facing slopes. 3. New loading will come close to shutting down this morning as winds drop to 15-20mph focusing our main concern on slabs created on Monday and Tuesday. Some of these should be on the upper end of the Moderate rating. 4. Expect variable conditions so be ready for constant changing surfaces under foot depending on where you travel. From sweating over a long slide on icy terrain one second, to triggering an avalanche the next, plan on encountering different hazards in both Ravines.
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 8:29a.m. Wednesday 2-13-2013. A new advisory will be issued tomorrow.
Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856