Avalanche Advisory for Wednesday February 20th, 2013

This advisory expires at midnight 2-20-2013

Tuckerman Ravine has HIGH, CONSIDERABLE, and MODERATE avalanche danger.  The Sluice, Lip, Center Bowl, and Chute have High avalanche danger.  Natural avalanches are likely and human triggered avalanches are very likely.  Very dangerous avalanche conditions exist. Travel in avalanche terrain is not recommended.  The Lobsterclaw, Right Gully, Left Gully and Hillman’s Highway have Considerable avalanche danger.  Natural avalanches are possible and human triggered avalanches are likely.  Dangerous avalanche conditions exist and conservative decision making is essential. The Lower Snowfields and the Little Headwall have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.

Huntington Ravine has CONSIDERABLE avalanche danger.  Natural avalanches are possible and human triggered avalanches are likely.  Dangerous avalanche conditions exist and conservative decision making is essential.

The summit has received approximately 4″ (12.5) of new snow, as have we down at Hermit Lake, with an additional 1-3″ expected through today.  Snow began last night around 5pm with winds from the S until about midnight when the shift began towards our current NW.  Southern winds associated with snowfall began with a velocity close to 40mph and fell through the evening into the teens. As winds transitioned to the NW through the early morning velocities increased again and have been gusting into the 60’s mph since dawn.  They are forecasted to continue rising, gusting over 70 later today.

As wind speeds slowed to 15mph around midnight, with new snow falling, a lighter “fist” hardness layer was deposited. In quick hand shears in my travels today I am getting easy shears on this unconsolidated soft layer.  This mid slab layer is the main weakness I am seeing this morning and the most likely issue leading to slab fracture and failure in the Ravines.

With cold air in place we are finding snow in the 5% range deposited in the trees down low.  However, in locations affected by the wind delicate stellars crystals are being destroyed into fragments, increasing the densities as shown at our snowplots and at the summit.  Therefore as winds continue to ramp up I expect slabs of increased hardness to be deposited over the early morning loose layer.  With this said this “increased” hardness is still likely pretty soft in sheltered locations, perhaps ”4 finger”, so anticipate new slabs to be delicate and reactive to human triggers.  As upslope snow continues today the increasing avalanche danger trend will continue.  Expect to see the potential of natural avalanches to be highest on the largest E and SE faces, with Tuckerman’s Lip and Center Bowl leading the charge.  It is likely that the forecasted snow tonight and tomorrow will continue our heightened avalanche dangers for Thursday.

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. 2-20-2013. 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

2013-02-20 Print Version