Posted 8:28am, Friday 3-25-2011
Tuckerman and Huntington Ravines have HIGH avalanche danger. Natural avalanches are likely and human triggered avalanches are very likely. Very dangerous avalanche conditions exist. Travel in avalanche terrain is not recommended. The only exception to this is the Little Headwall which has Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely.
Once again the mountains are giving weather forecasters a little surprise as they are forcing quite a bit of fluffy accumulation out of the clouds. As of midnight the summit of Washington reported 7.8” (20cm) of 3.8% low density snow. Snow density increased to 7.8% from midnight to 6am this morning as an additional 2.7” (7cm) fell for a total of 10.5” (26.5cm). This came in on a shifting wind beginning out of the E, moving to the N, and eventually coming from the NW Thursday afternoon. Wind speeds began very light upon precipitation initiation putting a thin low density inch or two across the mountain. I believe this undisturbed blanket will likely be the weak layer contributing to avalanche activity today. NW winds began to ramp up overnight reaching 35-40mph early this morning. These velocities are expected to continue today gusting higher occasionally from the NW and WNW. The very low density snow at temperatures between 5-10 degrees F will load into both Ravines creating a very sensitive touchy soft slab. I would also pay attention to these instabilities in unusual areas due to the very weak unconsolidated layer I just mentioned.
We have been monitoring the slabs deposited during Monday and Tuesday’s storm over the past couple of days. These have been on a stabilizing trend, but with the new snow overnight avalanche activity could step down into these slabs which are sitting on a very firm hard crust. To add to the instability problem is the presence of a very very thin sun crust that developed on a number of south aspects due to some short bursts of intense sun midweek. This crust now has a low density snow weakness above it with an increasing density slab building on top.
The Bulls-eye points:
- 10.5” (26.5cm) of new snow which began very light at 3.8% and became heavier albeit still quite dry at 7.8%.
- Winds began very light around 10-15mph as snow began and increased overnight gusting to 45mph this morning.
- Low density snow coupled with moderate wind velocities from the NW and WNW will generate very touchy soft slabs on a variety of aspects and slope angles.
- Additional snow is expected today as upslope conditions exist giving us perhaps 2 or 3 additional inches
- Expect numerous soft slab avalanche cycles as new snow quickly reloads in strong lee areas.
With the information I have right now I expect HIGH avalanche danger to exist into the weekend. Increasing winds on Saturday from the NW at 45-50mph in the morning to over 70mph in the afternoon will bring copious new snow into avalanche terrain. The touchy nature of new slabs may generate snow instabilities on the upper section of the winter Lion Head route above treeline. It will be important to stay on the route to avoid the majority of these issues. However, it is still possible unstable snow will exist on the route. It will be important to have good assessment skills. This is particularly true tomorrow as winds increase and more people acting as triggers will be out for the weekend. Be sure to check out our Weekend Update later today for more information on the projected issues for Saturday and Sunday.
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.
Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856