Avalanche Advisory for Friday, 1-20-2012

Expires at Midnight  Friday 1-20-2012

Tuckerman and Huntington Ravines have HIGH avalanche danger.  Natural avalanches are likely and human triggered avalanches are very likely.  Very dangerous avalanche conditions exist and travel in avalanche terrain is not recommended. This includes runout paths of avalanche activity such as the fan in Huntington and the floor of Tuckerman Ravine. The Lobster Claw, the Lower Snowfields, and the Little Headwall are not posted due to an overall lack of snow. Forecasts for these locations will begin when conditions warrant.

The mountain region received a nice unexpected punch of new snow last night vastly exceeding forecasts in numerous areas.  Pinkham Notch, up to the Hermit Lake elevation has received between 6 and 7” (15-18cm) of new snow.  Here at Hermit Lake it’s still snowing with a possibility of 2 more inches (5cm) through the morning. The more significant impact of this new snow is the low densities and moderate wind speeds today.  The snow density average between our manual snowplots is 3.5% which is very light, but not surprising with temperatures below zero F in the higher elevations.  I would expect some steep areas to sluff off due to the new snow’s lack of strength and cohesion.  In “stepped” or “benched” gullies you may see some deep pillows developing.  Some potential examples of this may be found under the ice pitches in Huntington’s Central, Pinnacle, and Odell gullies or across the Tuckerman Headwall in the Center Bowl.  In addition, light to moderate winds from the S last light, moving through the SW, and over to the NW late today will load all primary aspects in the two Ravines.  While this progresses, increasing wind velocities from 25 to 60mph (40-105kph) will develop denser slabs over very loose and unconsolidated snow acting as the weak layer at the interface with the old surface.  Hard and slick surface conditions in the Alpine zone at temperatures around -5F will not hold this cold snow very well.  Therefore today’s winds will have an easy time moving new snow from above treeline down into the avalanche prone slopes of the two Ravines.   Boiling all this down to a simple statement:  I believe delicate, touchy, soft slabs will develop over loose 3.5% density snow today on most aspects from North faces early, progressing rapidly through East faces, and eventually towards the South faces.  I would expect several rounds of natural avalanche activity to occur.  Cold air falling to -10F (-23.5C) tonight at upper elevations will not help consolidate any new soft slabs instabilities that develop today.  I would expect an elevated avalanche danger in at least some areas particularly those that don’t avalanche in the next 24 hours.  Although light, 1-2” (2.5-5cm) of snow forecasted for Saturday could cause a few additional problems.

The Lion Head summer trail becomes an increasing avalanche risk each winter just below treeline, eventually being closed when we open the winter route.  We took a good look at these vulnerable traverses yesterday and they are still peppered with anchors, i.e. brush, trees, and rocks with a limited bed surface.  However this fairly unusual snowfall with very low densities has me believe that a small soft slab or loose sluff is not out of the question.  This is due to the very low strength of any new snow in the deposition minimizing the impact of anchors.  Use caution in this area and use safe avalanche travel practices such as going one at a time.

The Sherburne Ski Trail has decent coverage at this time with a fresh 6-7” of fluff. Be cautious for some buried landmines and waterbars as they still are problem particularly when you can’t see them.   Check out the Weekend Update issued late in the day for any updates and tidbits we can pass along for your weekend trip planning.

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 8:40am. 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

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