Posted 8:25a.m., Sunday, January 2, 2011
Tuckerman and Huntington Ravines will have Low avalanche danger today. Natural and human triggered avalanches are unlikely except for isolated pockets in steep terrain.
We are seeing the light at the end of the tunnel as our December/January thaw rapidly comes to end over the next 12-24 hours. Before the warm air mass exits however it will give our snow pack one last punch and stranglehold today eating it up a little more before the cold air nudges it out of the region. Temperatures in the Ravines and their associated avalanche start zones have been in the 40-45F (4-7C) range quite a bit over the past couple of days and currently hover there waiting for some air mixing and increased winds later today. The slow increase in air temperatures on Thursday and Friday allowed our snowpack to adjust to these warm changes never pushing it over the edge to avalanche. We believe we reached peak instability yesterday and overnight before falling down the danger rating scale during the early morning darkness. We transitioned from Considerable to a Low forecast today because we believe the natural avalanche potential moved from being possible to unlikely. The decline in the avalanche potential of wet slabs will be a gradual process during the first part of the day as temperature moves from 45F (7C) towards freezing but melt water percolation and some additional light rain continue. When the mercury drops below 32F (0C) and the wet snowpack begins to freeze from the surface down the avalanche potential will plummet late in the day. This occurs due to a rapid increase in tensile strength with the development of our lovely New England boilerplate. Until this occurs we still have a minor concern about pockets that may have lubricated bed surfaces and are isolated and confined by surrounding terrain features. An example would be wet slabs overlying blue water ice in the Center Tuckerman Bowl and gullies in Huntington. Although we do believe avalanche activity is unlikely, snowpack stability does not usually make Hopscotch jumps from one danger rating to another instantly, it is a transitional process. So as of right now we have flowed from “possible” to “unlikely” and will continue declining until the cold air locks up all areas during the overnight.
The return of winter will be accompanied by the development of very hard snow surfaces and bountiful water ice. Expect all angled terrain to be very slick and hard making crampons and ice axes imperative along with the experience to use them. A sliding backpack down one of the Ravines would likely break the sound barrier tomorrow as temperatures hit 0F (-18C) tonight on the higher summits turning slopes into inclined hockey rinks without the boards. Ice climbers should also be prepared for ice dam development as water channels under the existing ice become blocked, backing up water and increasing the pressure. This phenomenon can have impressive and powerful results when discharged by a crampon kick or tool placement.
- 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