This advisory expires at 12:00 midnight, March 1, 2013
Tuckerman Ravine and Huntington Ravine have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully. The only exceptions to this rating are the Lower Snowfields and the Little Headwall, which have Low avalanche danger. Natural and human triggered avalanches are unlikely.
There are two contexts in which to be looking at snow stability today. First is related to the after-effects of the recent storm, i.e. existing stability problems. Next is how the weather forecast is going to play out, with the potential for increasing avalanche danger due to new snow and additional wind loading. Overall, this is a complex snowpack that deserves respect. If you know what to look for you may be able to seek and find reasonably stable snow, or you might find snow that scares you more than the threat of sequestration ever would.
Without getting too deeply into the weeds about how exactly the storm played out, I think it’s accurate to say that the mountain fared well. Approximately 15″ (38cm) of snow fell on the summit and we saw a little under a foot at Hermit Lake. During much of the storm, winds were strong from the ESE. Yesterday, they shifted to the NW but died off into the single digits for many hours. Overnight wind speeds rose again into the 30-40mph (50-65kph) range from the NW. Current stability problems can be found on many aspects. Those with a north-facing component were loaded during the ESE winds and snowfall; those with an E or S aspect saw further loading last night while winds blew from the NW. S-facing slopes such as Right Gully received solar gain and had a moist surface layer yesterday. Some forecast areas, such as the Lip, Center Bowl, Central, and Odell Gully will be at the upper end of the Moderate rating. Remember that the topography of our ravines creates conditions with high variability as you move from one location to another. This phenomenon is heightened when winds have been shifty and the sun is at work. You should be carefully assessing snow throughout your entire route. If solar energy is able to penetrate again today, there may be some stabilizing effect on S-facing slopes.
The issue of today’s weather will need to be on your mind as well. This is what might cause avalanche danger to exceed the posted ratings in some locations. Currently there is some snow being blown down the Lip and headwall of Tuckerman and in many gullies of Huntington. We don’t believe this additional loading on its own is enough to bump ratings into Considerable, but it is slowly accumulating and adding load to existing slabs. Furthermore, a light amount of new snow may fall today. It’s hard to believe this when you look up from Hermit Lake and see clear blue skies, but the NWS forecasted about an inch and the Observatory forecasted 1-3″. Based on what we’re seeing, we think 1″ is the more likely scenario. But, if we do get more than that today and winds are blowing from the NW at 30-40mph, the instabilities mentioned above will continue to develop. This may push danger ratings above Moderate in some areas. If we get nothing at all, then we will remain in the Moderate range.
The lower half of the Sherburne went above freezing for a little while yesterday. Expect varying conditions from top to bottom.
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.
Posted 8:35a.m., March 1, 2013. A new advisory will be issued tomorrow.
Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forests
(603) 466-2713 TTY (603) 466-2856