This advisory expires at 12:00 midnight, Monday December 30, 2013
The Lion Head Summer Trail is now closed. Please use the Lion Head Winter Route.
Tuckerman and Huntington Ravines have HIGH avalanche danger today. Very dangerous avalanche conditions exist. Travel in avalanche terrain is not recommended. Natural avalanches are likely and human triggered avalanches are very likely. Exceptions to this rating include Lobster Claw, Right Gully, and the Lower Snowfields in Tuckerman which have CONSIDERABLE avalanche danger. Natural avalanches are possible and human triggered avalanches are likely in these areas. The Little Headwall has Moderate avalanche danger. Human triggered avalanches are possible.
AVALANCHE PROBLEM: As mentioned, TRAVEL IN AVALANCHE TERRAIN IS NOT RECOMMENDED. This includes walking up into the low angled terrain at the base of either ravine. You do not need to be on a steep slope to be within striking distance of naturally triggered avalanches today. I expect there will be multiple avalanches in many of our forecast areas. The primary problem is storm slabs that began to build last night and will continue to develop as winds are able redistribute significant amounts of snow today.
WEATHER: The recent storm is one to make us smile. Storm totals as of this morning were 13.2” (33cm) at the summit, 12” (31cm) at Hermit Lake, and 11” (28cm) at Harvard Cabin. Densities are consistent at about 8-9% at each location. At the onset of snowfall, winds were fairly light, coming from the E in the 15-25mph range. With heavy snow falling overnight, winds swung counter-clockwise and steadily increased velocity. At 7a.m. today they are blowing from the W in the 60-80mph range. The speeds are expected to remain strong, although the direction will shift back a bit towards the NW. Temperatures will be falling through the next 12 hours to below zero F. Expect a significant amount of windblown snow if you go above treeline today.
SNOWPACK: About one week ago the mountain fell back below freezing after a prolonged December thaw. This created an icy crust that was a dominant surface condition in many locations this past week. A few inches of light density snow had fallen during the week and were loaded into windslabs located in the strongly sheltered locations in the ravines. One of these slabs, in the Lip area, proved itself unstable on Saturday evening as a party of two hikers triggered an avalanche that carried them to the floor of Tuckerman.
These two surface conditions, the icy crust and the sensitive windslabs, are what the new snow has fallen onto. With the winds slowly ramping up during the storm, we likely had some avalanche activity overnight as denser slabs were able to build on top of relatively weaker snow that had not been wind-effected. If a path has not yet slid, it will have this very weak layer waiting for sufficient load to release it. If it has already slid, then we can expect continued reloading of new slab onto an existing bed surface. All this equates to a strong likelihood of avalanche activity in most areas today.
The areas not posted at High danger have only begun to fill in with snow for the season, so they have smaller potential bed surfaces. Recreational opportunities are limited in these areas (i.e. the bushwacking is miserable) but you should remember that Considerable is still a dangerous rating in which to be out recreating.
Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856