Posted 8:23a.m., Wednesday, January 19, 2011
All forecast areas in Tuckerman and Huntington Ravines have CONSIDERABLE avalanche danger today. Natural avalanches are possible and human-triggered avalanches are likely. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential.
For a while yesterday I wondered if the snow was actually going to amount to anything. It seemed like it had been snowing all morning but there was little to show for it. Sure, there were some drifts but it seemed like we had little more than a skim coat on the existing snowpack. Luckily things picked up in the afternoon and by midnight the summit had picked up 8.3” (21cm) of snow with an average density of 7%. Less than an inch has fallen up top since then but temperatures have remained below freezing. At Hermit Lake we had 6” (15cm) of snow at the snowplot this morning but this only tells part of the story. The top inch (2.5cm) of the new snow is heavy and wet which leads me to believe that we picked up even more before settlement occurred. How high up the mountain this wet layer extends will be the focus of our fieldwork in the coming days. Hopefully it will get buried before it cools down and becomes a crust.
Winds stayed out of the SSW, S and SE until 4AM this morning when they swung around to the WNW. Speeds during the heaviest snowfall yesterday were between 40 & 60mph (64 & 97kph) with a daily average at the summit of 46mph (74kph). During this period aspects with a northerly component picked up a fair amount of snow through wind transport and if we weren’t socked in I’m sure we’d see evidence of an avalanche cycle. These aspects received a Considerable rating today due to the possibility of human-triggered avalanches within the storm snow or at its interface with the old surface. By midnight the winds were in steady decline and little oomph was left when they spun around to the WNW. Southerly aspects saw limited loading during this storm event so why the Considerable rating there too you wonder? Prior to this storm S aspects held the instabilities of most concern. Some areas like the Lobster Claw, Right Gully and Damnation showed evidence of avalanche activity but all areas either reloaded or held “hangfire” (pieces of a failed slab that have hung on while the remainder avalanched). Snow from the past 24 hours likely built a limited amount of new windslab in these areas but it did add additional load to already suspect slopes. As temperatures drop today and snow showers continue these areas will be the first to receive additional loading if winds hang at the upper end of their forecasted range. Easterly aspects have been cross-loaded by most of our recent storms and had one good period of direct loading before this event. They will likely harbor the greatest spatial variability in terms of instability. Concerns with human-triggered avalanches override our concerns with natural triggers in all areas today.
The Sherburne Ski Trail has been providing great turns but a developing crust may impact your experience. Watch your tips as the snowpack was thin to nonexistent just one week ago. If you’re thinking of going to the summit in the coming days make sure you check back here to see the current status of Lion Head. We’ll be making the shift to the Winter Route later in the week and if you’re watching the advisory you’ll be the first to know.
- 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.
- This advisory expires at midnight. A new advisory will be issued tomorrow.
Justin Preisendorfer, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856