Posted 8:00a.m., Monday, February 28th, 2011
Tuckerman and Huntington Ravines have HIGH avalanche danger. Natural avalanches are likely and human triggered avalanches are very likely. Travel in avalanche terrain is not recommended. The only exception to this rating is the Little Headwall in Tuckerman Ravine which has Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.
We have a high degree of confidence that today’s conditions will result in numerous natural avalanches in both Ravines. A winter storm is forecasted to dump 7-10″ (18 to 25.5 cm) of snow and sleet in the mountains before changing over to freezing rain this afternoon. Winds are forecasted to be out of the S, shifting to the SW and increasing to 50 to 70 mph (80 to 113 kph) during the day. Tonight, winds will continue shifting until finding a home out of the NW and increasing to 70 to 90 mph (113 to 145 kph) with gusts forecasted over 100 mph (161 kph). There are a number of blatant clues telling us that snow stability will be poor today. The snow that is falling right now is landing on yesterday’s snow that totaled around 2-3″ (5 to 7.5 cm). Yesterday’s snow was remarkably light with a density around 4%. This will provide an ideal weak layer for the first round of avalanches today. As much as I hate to accept it, warm air will be nudging its way into the mountains causing today’s snowfall to increase in density and ultimately transition to sleet. This will continue the theme of an upside down snowpack with lighter snow becoming buried by increasingly heavier snow. Wind loading aside, this is a red flag when it comes to snow stability and will be an issue on all aspects. I suspect these details will be subtle in comparison to the dramatic effect wind loading will have on snow stability today. The shifting and increasing winds will transport copious amounts of new snow onto all aspects of the ravines and create wind slabs of increasing density as the day wears on. When you put all of these variables together it is hard to figure a way that avalanches won’t occur. The fun doesn’t end there! Freezing rain could create some intense glazing later this afternoon which will make you wish you were wearing a house rather than your fancy parka. Depending on how much freezing rain accumulates, some of the snow could become encapsulated by a crusty layer. The increasing winds should do a good job at ripping this to shreds overnight but we will have to wait and see how it all plays out. It is worth noting that today’s avalanches could step down into older wind slabs that were deposited on Friday and Saturday resulting in some sizable slides.
The warm air that will move in today will be quickly booted out by very cold air once the winds shift to the NW. Tomorrow’s summits forecast is calling for mostly sunny skies but winds will still be quite strong and temperatures will struggle to reach the single digits F. Aside from a minor weather disturbance on Wednesday, it looks like the rest of the week will be quiet with plenty of cold air.
- 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.
Brian Johnston, Snow Ranger
USDA Forest Service, White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856