Avalanche Advisory for Thursday February 21, 2013

Expires at Midnight Thursday 2-21-2013

Tuckerman Ravine has CONSIDERABLE, MODERATE and LOW avalanche danger.  Right Gully, the Sluice, Lip and Center Bowl have Considerable avalanche danger.  Natural avalanches are possible and human triggered avalanches are likely.  Dangerous avalanche conditions exist. Careful snowpack evaluation, cautious route finding and conservative decision making is essential.  The Lobsterclaw, the Chute, Left Gully and Hillman’s Highway have Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible. The Lower Snowfields and the Little Headwall have Low avalanche danger.

Huntington Ravine has MODERATE avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible.

Over the past 36 hours the summit has picked up 8.1” (20.5”) of upslope snow with an additional 1-3” (2.5-7.5cm) expected today.  While this 8”of snow fell winds have been active moving from the S to the N with velocities in the teens up to yesterday’s max of 102 mph (165kph).  Temperatures have also been quite cold, falling to -8F (-22C) keeping the dominate crystal as stellars and plates which have been easily broken up and transported into lee areas.  In hindsight yesterday’s rating were on the money as witnessed by new fracture lines such as in the Center bowl right under the headwall ice.  This has undoubtedly helped fill in the Ravine floor a bit as it’s in desperate need of some good avalanche cycles to cover the wide spread vegetation that still exists. Some brief clearing on the southern end of both ravines gave us short glimpse of how this entire snow event has been playing out.  Unfortunately, areas of most concern today on the northern side of Tuckerman and Huntington are still shrouded in a cloak of blowing snow and fog.

Since the high winds last night the mountain has seen a couple of inches of snow with more forecasted for today.  These 2 inches came in on a decreasing wind from the WNW and NW to the current average in the 40’s mph (60’s kph).  As the day continues winds should wrap to come from the N and increase back up to 60-80 mph (97-129kph) with higher gusts.  This should start another loading event picking up snow lying in alpine zones that will be vulnerable to a compass rose wind shift and higher speeds.  New snow from the sky will also mix in with the redistributed snow, loading in slopes with a south facing component.  Although North gully and the Lobster claw are south facing, they have smaller bed surfaces than their neighboring sister paths.  Therefore, they are less of a concern than Damnation, Yale, and Central gully in Huntington and Right Gully, Sluice, and the Lip in Tuckerman.  These locations may be on the upper end of their Moderate and Considerable ratings depending exactly how wind speeds and new accumulations play out today.

Avalanche classes would have a worthwhile experience in the field today because there is so much good evidence that we have instabilities susceptible to natural and human triggers.  Large drifts on approach trails; Fist and 4 finger soft slabs over lower density snow; stability tests likely producing a mix of “yellow” and “red” light results; and visible wind transport of snow are several bulls-eye clues that a cautious conservative approach would be important in many locations.  The south faces that will likely get the new slab deposition today will be dealing with a potential new factor tomorrow-solar gain.  Clear skies, warmer temperature and low winds are expected so anticipate some continued stability problems tomorrow albeit a different fire breathing dragon.

The Sherburne ski trail should be a great alternative to venturing into avalanche terrain.  Expect some variable conditions due to some high winds but overall good skiing can be expected.

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 8:39 2-21-2013. 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

2013-02-21 Print Version