Avalanche Advisory for Friday, 3-02-2012

This advisory expires at midnight, Friday 3-02-2012

 Tuckerman and Huntington Ravines have CONSIDERABLE avalanche danger.  Natural avalanches are possible and human triggered avalanches are likely.  Dangerous avalanche conditions exist therefore careful snowpack evaluation, cautious route finding and conservative route finding is essential.  The only exception to this is the Little Headwall which has Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features.

  Averaging our Harvard and Hermit Lake manual snow plots we picked up about 12” (30cm) of new snow from this storm.  We saw the evidence of multiple avalanches particularly in Huntington due in part to the gullies being a bit steeper in places and more water-ice present.  Sluffs occurring off of steep slopes and blue ice was the likely trigger for numerous very soft slab releases.  Our ridge top field time yesterday proved that our assumptions were correct, and we encountered very delicate soft slabs with little strength.  Storm snow densities averaged about 7%, however as the storm progressed densities decreased with the top 4” (10cm) only coming in at 4%.  This is important not only because it’s champagne powder under ski, but because it will be very easy to move with an increasing wind.  Summit winds are forecasted to escalate and shift from the current direction of W at 20mph to SW and 35mph later.  Only slight ridge top winds will be needed to move this low density snow down into the upper start zones to once again create delicate soft slabs loaded on loose unconsolidated snow.  This will increase the possibility of natural avalanche activity which has forced us to the “Considerable” rating decision.  A number of locations are currently at the upper end of the Moderate rating, but this should change through the day.  So the big bulls-eye factor to watch today is wind speed and EXACTLY what speeds they increase to.  If you notice any snow transport going on, even low ground level drifting; expect very touchy slabs to be developing. 

The other big news that I have been referring to over the past couple of days is the ramping up of wind velocities tonight and over the weekend.  Tonight winds will continue shifting to come from the S and increase to 60+mph (96kph) with more snow.  This is by far the highest speeds we have seen since the recent storm began.  These winds will whip up the blanket of alpine zone snow and pour it into avalanche terrain over a weak loose snow layer.  Then tomorrow, winds will shift back to the W and approach raging levels at 80 perhaps gusting to 100mph with more snow!  It is quite plausible the upper elevations will remain all snow from the precipitation tonight and tomorrow, with enough water equivalent to give up over 6” (15cm) of the white stuff.  I would anticipate “High” danger ratings for numerous locations on Saturday.  Check in to our “Weekend Update” later today for updates on this developing situation.

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 8:45a.m. 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
www.mountwashingtonavalanchecenter.org

2012-03-02 Print Version