This advisory expires at midnight, Saturday 3-03-2012.
All forecast areas of Tuckerman Ravine have Considerable avalanche danger today. Natural avalanches are possible; human triggered avalanches are likely. Two exceptions to this rating: the Lower Snowfields have Moderate avalanche danger, natural avalanches are unlikely and human triggered avalanches are possible, and the Little Headwall, which has Low avalanche danger.
Huntington Ravine has Considerable and Moderate avalanche danger today. Central, Pinnacle, Odell, and South Gullies have Considerable danger. Natural avalanches are possible and human triggered avalanches are likely. North, Damnation, Yale, and the Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanche are possible.
We’ve got a fairly complex set of variables to wrestle with this morning, including recent weather history, avalanche activity, and forecasted weather, so bear with me as I do my best to distill these down into something useful. What we’re dealing with for snow stability is the aftermath of Thursday’s heavy snowstorm. In case you missed it, we received over a foot of light density snow while winds were out of the SE and E. Winds have since shifted back and forth from the W to the S and are currently from the W again. Summit wind speeds last night got very strong, gusting to 99mph (160kph), but we are suspicious that the strongest winds stayed aloft and did not push very far below the summit. The lack of wind-scouring in places such as Hillman’s is an important clue toward this suspicion. In Huntington the upper reaches of the gullies received some scouring, but the middle and lower sections were more loaded than we’d expect after this weather pattern. Meanwhile yesterday, the mountain warmed up and some freezing drizzle created a thin crust everywhere except underneath tree cover. Although it received some freezing rain or drizzle, the uppermost elevations of Mt. Washington did stay below freezing. The avalanche activity we can observe this morning is also less than we would have expected with yesterdays weather, and it’s difficult to determine when exactly these took place. I’m confident enough to say that numerous avalanches have happened in several areas since Friday night, when winds started to pick up.
So starting out today, we’ve got numerous forecast areas that are preloaded with fresh new slab. Based on recent activity, it’s a safe assumption to say these newly developed slabs have some existing instability problems. Currently, many places are in the upper end of the Moderate rating, such as midsections of Odell and South in Huntington and the Sluice, Lip, and Hillman’s in Tuckerman. Today’s weather forecast calls for a chance of additional snow, though only a trace to 2” (5cm) is expected and most of this will come in the afternoon as a weak cold front passes by. Winds will be from the W and decreasing in velocity, but I would expect the speeds to be sufficient to deposit any new snow onto the already loaded slopes. This will drive the avalanche hazard from the upper end of Moderate solidly into the realm of Considerable. Not only will naturally-triggered avalanches be possible, but the likelihood of a person triggering a slide will be elevated as well. If new snow accumulations don’t materialize, actual avalanche hazard in the Considerable rated locations will continue hover between Moderate and Considerable. If the upslope snow guns start up earlier and heavier than expected, then the trend will be toward increasingly unstable snow.
- 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 8:45a.m. A new advisory will be issued tomorrow.
Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856