This advisory expires at midnight Friday, 3-09-2012
Tuckerman Ravine has Considerable and Moderate avalanche danger. The Sluice, Lip, and Center Bowl have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The only exception to this is the Little Headwall which has Low avalanche danger. Natural and human triggered avalanches are unlikely.
Huntington Ravine has Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully and identify features of concern.
Winter decided to go on sabbatical over the last couple of days to learn a few things about being harsh, allowing its nemesis, Summer, to take over the region. The Mount Washington Valley climbed into the mid sixties F yesterday, while avalanche terrain said hello to about 50F with the onset of rain in the early evening. Well, Winter’s thoughtful time away made him anxious to get back so he came raging back in like a freight train overnight hitting 120mph at 7pm. Temperatures dropped from 36F at 11pm to 4F this morning, enabling the transition from rain to snow. The summit recorded 0.3” of rain that fell from 6 to 11pm before snow began, giving us 2.1” as of 6am this morning. Down here at Hermit Lake we have received +/-3” since the rainfall yesterday. The precipitation type that changed over last night has allowed for good initial adhesion at the interface between new snow and the old wet surface. As new slabs develop in the strong lee, such as under the Tuckerman Headwall ice, Lip, and Sluice, failure would occur above this interface in new snow. Areas blown clear by high winds the surface are now cold and slick, although textured with lots of nooks and crannies. New snow bonding in these locations won’t be as good due to cold icy surfaces, but that should start to occur late today as wind speeds plummet. The other factor to consider is how the new, growing snowfields are insulating the warm 0C snow underneath at varying levels. This will add to the spatial variability in regards to facet growth rates and bonding of new snow making for a shambolic situation.
Today’s avalanche ratings are all due to new snow, not the old, warm snow which will continue to lock up with dropping temperatures. The bulls-eye points today are reasonably straight forward. First, between 2 and 3” (5-7.5cm) of new snow has fallen and it’s still snowing at a half an inch (1cm) an hour intensity rate (S-1). Second, loading winds from the WNW at 67 gusting to 83mph is moving snow from the alpine zones down into both Ravines. And third, as wind diminish through the day new snow will load into lee terrain more readily lowering the scouring rate, particularly in Huntington Ravine. These factors create concern for the possibility of natural avalanches in several lee areas in Tuckerman, forcing the Considerable rating for the Sluice, Lip, and Center Bowl. Locations adjacent to these 3 forecast areas, namely Right Gully, Left Gully and particularly the Chute should be bumping against the ceiling of the Moderate rating. In Huntington, where all forecast areas have Moderate avalanche danger, we have the most concern about Central, Pinnacle, and Odell. They also may be knocking on the Considerable door, as snow loads below the lower ice, near the approaches experience frequent sluffing and spindrift activity. Due to the very high winds overnight you will undoubtedly find scoured sections down low in both Ravines as well as narrow locales where wind vortexs are higher. Realize you may be on old surface during approaches but that may change once on route. Low visibility for a good portion of the day will hamper quality route assessment.
Off trail travel will still be tough without floatation so skis or snowshoes are recommended. Open water holes are still present in the brook when leaving the floor of the Ravine, use caution when traveling through this area. Check out “Weekend Update” later today for additional information for the next couple of days and be sure to read Saturday morning’s avalanche advisory before heading up to the Ravines.
Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856