This advisory expires at midnight, Saturday 3-10-2012
Tuckerman Ravine has Moderate and Low avalanche danger. The Lower Snowfields and the Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.
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.
Extreme wind dominated the early part of yesterday on the higher summits. Mount Washington hit 114mph (185kph) from the NW before rapidly subsiding through the day. Certainly these early velocities did their job to scour many locations, with the exception of strong lee areas. Clouds still envelope the hills, playing with us, occasionally giving a glimpse of what occurred overnight. Staying at the ready with binoculars allowed some clues to jump out, helping us ascertain what issues are held in Tuckerman this morning. As of this writing Huntington is still enshrouded in fog and clouds. After the high winds decreased in speed on Friday, snowfall continued and added up to about another inch (2.5cm), while down at the 3800ft level between 1 and 2” (2.5-5cm) fell. The final inch was very light in density at 4%, allowing low wind speeds to load snow into avalanche terrain. In total, over the past 32 hours the summit picked up 3.1” (7.5cm) while Hermit Lake hit a bit over 4” (10cm). Based on how winds played out during this period I would expect quite variable conditions, from scouring on exposed slopes with a dusting of new snow, to some unstable slabs in our stronger lee terrain of W and NW winds. Generally you will find the full range within the definition of “Moderate” from the lower end near, but not quite in “Low”; and a solid Moderate particularly under the Tuckerman Headwall ice over through the Sluice to the north. This steep area is very well protected even from extreme western winds. The experienced and avalanche skilled traveler, doing constant evaluation of stability and route choices, should find some reasonable options. In Huntington, we believe more scouring and wind ripping of the terrain occurred. But due to clouds we can’t confirm whether or not we have only isolated pockets of concern, a definition component of a Low rating, or slightly greater snowfields more in line with a Moderate rating. Because many of the gullies are so narrow the difference in snowfield sizes may only be several meters between ratings. Very often pockets of instability that can be easily avoided may deserve a Low forecast, while a choked gully with no options but to plod through new slabs or descend may receive a Moderate rating. We are currently in this delicate scenario forcing us to a”Moderate” choice due to hampered visibility.
Winds are expected to slowly increase in speed from the current of 20mph (32kph) to 50+ mph (80kph) tonight. The low density snow that fell yesterday during winds between 10 and 40mph (16-64kph) will begin to be loaded at some point in the velocity transition. Therefore, watch for snow loading activity later in the day and be ready to deal with an increasing danger by altering plans if needed. All weather data indicates this shouldn’t happen until after dark, but a slight wind speed forecast error could make the difference for loading today so keep your eyes open. Although clouds should keep heating at bay, watch for solar gain potential on southern aspects if long periods of direct sun coincide with today’s low winds. This may increase the possibility of sluffing and a very remote chance of a slab failure. In general, I think it will be a nice winter day to be above treeline due to light winds and reasonable temperatures climbing close to 10 degrees F (-12C).
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. The open holes on the Little Headwall are increasing in size and may not be visible from above.
Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856