This advisory expires at Midnight tonight.
Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger. Central, Pinnacle and Odell Gully have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. North, Damnation, Yale, South and Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.
Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. The Lip, Center Bowl, Chute, Left Gully and Hillmans Highway have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Lobster Claw and Right Gully have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Lower Snowfields and Little Headwall are not rated due to lack of snow.
AVALANCHE PROBLEM: New snow yesterday, combined with the potential for new snow today on increasing wind speeds from the west, will build wind slabs. These wind slabs have the potential to be sensitive to human triggering as well as to increased loading. Travel in avalanche terrain will be further complicated by poor visibility. A melt freeze crust on old bed surfaces with associated facets in shady aspects is also a concern. We have a dynamic snowpack right now and with rapidly changing weather today, would be travelers in our terrain would be hard-pressed to do so safely. These avalanches most likely won’t be large in most areas but the runouts are particularly unforgiving right now with boulders, cliffs and stout bushes making any avalanche potentially dangerous.
WEATHER: Over the past 36 hours, wind speeds have been relatively light and have loaded in 4” of low density snow. Today, a trough may continue to send potentially heavy snow squalls in our direction from the Great Lakes. The rate of snowfall this morning indicates that we will soon reach or exceed the NWS forecast of 1-2” and the MWObs forecast of a trace to 1”. Though these amounts don’t seem like much, history as shown that a smooth fetch zone in the alpine zone can give up this snow to the wind and rapidly build sizable wind slabs. As winds increase today, snow will become more densely packed (lots of Tuckerman terrain) or scoured out (northern Huntington gullies) but not before passing through peak probability of natural and human triggering. Temperatures will continue down to -20’s F below zero.
SNOWPACK: Some snow that survived warm November conditions was coated by the widespread snow/rain slush mix that now coats everything at higher elevations, including some older snow in shady aspects on the lookers left of both Ravines. This month, the summit has recorded 52” of snow which is roughly twice the normal amount. Only a few brief spells of hurricane force winds have pummeled and scoured our snowpack which has contributed to our protracted spell of elevated avalanche danger. Multiple avalanche cycles have occurred, mostly in the upper layers of the snowpack. A lingering concern for me now is the buried melt/freeze crust that exists in those shady, more continuous and larger slopes with the oldest bed surfaces, primarily Center Bowl, Chute and Left. Cold temperatures tell me it is probably faceting in some areas. That said, the primary concern remains new wind slabs from today’s squalls and increasing wind.
The Lion Head Summer Trail remains the better route to the summit. Remember that the bridge work continues on the Tuckerman Ravine Trail so use the detour on the Huntington Ravine Trail. Many people are using the Sherburne as an uphill route; please be on the lookout for these people as well as machinery that is using the Sherburne as the access to the construction site. We hope to reopen the Tuckerman Ravine trail soon. Thanks for your continued patience.
- 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 8:00 a.m., Thursday, December 15, 2016. A new advisory will be issued tomorrow.
Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2716