(We apologize for the advisory’s late internet posting. Due to riming and dense fog our wireless internet connection was down on the mountain. In addition, other computer issues complicated this primary problem. On mountain hard copies were posted on time.)
This advisory expires at midnight.
Tuckerman and Huntington Ravines have LOW avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features.
Yesterday the summit picked up a mix of precipitation types, but unfortunately rain dominated the mountains through the overnight. Periods of heavy rain between dusk and midnight caused some brooks to blow out, although generally we seemed to have survived pretty well. The main upper Cutler River branch from Hermit Lake to the first bridge on the way down on upper Tuckerman trail is still snow covered. The branch coming out of Huntington blew out a bit around 9pm as noted by the Harvard Cabin Caretaker. In the end the summit picked 0.7” of snow followed by an inch of rain and freezing rain. Thick fog is hampering visibility into either Ravine so knowing if any havoc occurred on the slopes is still unknown. I can’t even tell you if the Little Headwall blew out, which is quite close to Hermit Lake, the visibility is so bad.
Taking a look at the high water marks of brooks leading into the Ravines it’s clear we’ve come down substantially since the peak flow, showing the snowpack has drained quickly. This fact associated with a drop in temperatures, recently falling below freezing at Hermit Lake and the Harvard Cabin, is causing the snowpack to stabilize. The avalanche danger has fallen rapidly through the early morning and will continue to do so today as summit temperatures drop to the teens F. (-8/-9 C). This will freeze the snowpack from the surface down creating a thicker and thicker hard eggshell layer into tomorrow. This developing concrete-like bridge is hitting the reset button, making all the issues we have been tracking for weeks moot. This new surface layer will now do two main things in the short term. First, it will be a slick bed surface for new snow to load on with some extreme temperature gradient potentials. And second, it will be a slick surface for you to slide on. Over the next day snow surfaces will get very hard and slick. Ice ax, crampons and mountaineering skill will be essential to travel safely. A heavy dense package covered in low friction Gore-Tex will reach terminal velocity very quickly in case of a fall. Split second immediate self-arrest with your ax will be imperative before Mach speeds are achieved.
Some other hazards to consider are some of the early signs of spring. Some crevasses may have opened up during this event but this is an unknown. Historically areas in Tuckerman’s Lip towards the Center Bowl and down to the floor transition are the first places for them to appear. Also, expect weak snow bridges over running water until late in the day as freezing solidifies them. The main hazard for ice climbers are the development of ice dams. After winter thaws and rain events water flowing behind water ice starts to become constricted as refreezing begins. This starts to build up pressure as pinch point can’t accommodate the volume of water that is backing up above these locations. This water wants out bad and it will take any opportunity to make it happen, often taking full advantage of your tool or crampon placement to release with dramatic effects. Many ice climbing accidents have been caused by ice dams. The highest risk of this will occur late today and tomorrow.
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. Completed 8:43 posted 10:30 3-13-2013. A new advisory will be issued tomorrow.
Christopher Joosen, Snow Ranger USDA Forest Service White Mountain National Forest