Avalanche Advisory for Friday, February 5, 2016

Tuckerman and Huntington Ravine will have MODERATE avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible.  Heightened avalanche conditions on specific terrain features exist.  Evaluate snow and terrain carefully to identify features of concern. Lobster Claw, Lower Snowfields, and the Little Headwall in Tuckerman Ravine and North, Damnation, Yale and the Escape Hatch in Huntington Ravine are not posted due to lack of snow cover. Exercise caution in these areas and expect the potential for isolated patches of instability in larger snowfields.

 AVALANCHE PROBLEM: New Wind Slabs will be the developing avalanche problem today.  All areas are starting the day at Low avalanche danger with widespread hard old surfaces. New snow and building winds will develop new low to moderate density thin slabs on slick bed surfaces through the day.  Anticipate larger snowfields to push through the Moderate rating hedging towards Considerable if we reach the upper end of the precipitation forecast.

WEATHER: At dawn the summit is beginning to receive snow with a temperature of 10F (-12C) and winds from the W at 15mph (24kph).  Snow is expected to continue into the afternoon totaling 2-4″ (5-10cm), causing very low visibility above treeline due to a ramping and shifting wind. Expect velocities to climb from the relatively placid conditions currently, to over hurricane force (77mph) from the NW.  The mercury will fall to about 0F (-18C) overnight with a peak wind around 90mph (144kph).  Continued snow through the weekend, albeit light, will continue Wind Slab problems for the next few days.

SNOWPACK: Thirteen hours above freezing on the summit Wednesday night and Thursday morning, along with 0.5″ (1.25cm) of liquid precipitation, has given our upper snowpack a “reset button” effect.  I say this because, temporarily, it has made the vast majority of snowpack weaknesses that existed before the thaw moot.  The wet snow settled and began re-freezing near the surface as the mercury fell.  This created very strong surfaces that have begun to bridge over wet snow below. I say “temporarily” above because I suspect will go to facets fairly quickly depending on the amount of new snow insulation that occurs this week.  We’ll watch how that develops. So…currently this new hard slick bed surface is receiving new snow, forecasted between 2-4″, from a system moving up from the S.  We are on the northern edge of this precipitation shield so we could end up on the very low end of expected amounts, but some banding has been occurring that may lay down a significant blanket in areas not too far from the Presidential range.  Will this be our reality as well?  We’ll see.  New snow should begin to act as a loose unconsolidated layer on slick bed surfaces.   In the steepest of Ravine areas it may very well sluff off, accumulating on benches and lower angled slopes below.  On other slopes there may be just enough friction to stay in place while an increasing wind builds a wind slab, with increasing density, over this new weak layer.  I would anticipate any new slabs you encounter to be touchy based on this weak layer and the poor initial bonding with the old surface.  Although I consider natural avalanche potential to be unlikely today, if we reach the upper end of the snow totals and high winds earlier, you should expect the potential for natural avalanches to shift towards being possible.  So have the potential for Considerable danger in your head late this afternoon.

ADDITIONAL ISSUES:  

  • Climbers should expect the potential for some ice dams under hydraulic pressure due to the recent thaw and refreeze.
  • Anticipate a randomly breakable crust catching you off guard.  Move deliberately and with caution particularly as you descend steep slopes near brush and rock which will likely cause weaker snow bridging.
  •  Slick surfaces will make for long sliding falls into the rocks if you slip.  Immediate self arrest is critical with your ice ax and experience.  Otherwise, a good outcome is very unlikely.
  • The Lion Head Winter Route is open and is recommended for those opting to avoid avalanche terrain in the early season. Expect some thin, scratchy sections of ice and rock in the steep sections. Microspikes and ski poles are helpful on lower elevation trails, but are not substitutes for crampons and an ice axe on this route.
  • The John Sherburne Ski Trail is survival skiing.  Expect rocks, ice, bare sections, with additional challenges as a thin new snowfall hides these landmines.

Please Remember:

· 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 8:30 a.m. February 5, 2016. 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

2016-02-05