Avlanche Advisory for Thursday, February 20, 2014

This advisory expires at Midnight.

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

All forecast areas in Huntington Ravine have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Careful snowpack evaluation, cautious route finding and conservative decision making is essential.

AVALANCHE PROBLEMS: Our nemesis the Wind Slab is here again as our primary avalanche problem. West-northwest wind ramped up late yesterday morning and loaded east facing start zones. Somewhere in the neighborhood of 5” of new snow in the past 24 hours yielded plenty of raw material for these slabs to form. Strong winds near 80 mph (128 kph) and gusting into the 90 mph range (145 kph) typically load lower start zones such as beneath the main ice floes in Central and Center Bowl and in the sheltered mid sections of gullies such as South, Escape Hatch, Left and Hillmans. These slabs have grown considerably in the past few days with not a lot of opportunity to stabilize.

WEATHER: Reduced visibility due to a summit cloud cap will hamper assessment this morning, though some afternoon clearing may occur before the next wave of higher clouds and precipitation rolls in tonight. Gusts from the NW this morning are continuing to push into the 90’s mph (140’s kph) and hit 100 mph (160 kph) around 7:30 am, but will shift to the West and slow to the 60’s mph (90’s kph)this afternoon.

SNOWPACK: New loading in the past 24 hours is an obvious concern in the snowpack. This new load is sitting on a grain size change and probably a hardness difference across the fracture plane marked by the wind ramping up yesterday morning. Wind speed has been high enough to create hard slab avalanche potential in many areas and due to the rapid loading we feel that natural avalanches are possible today. These windslabs may be firm (1F) but be sure to consider the softer, weaker layer which may be pretty deep but somewhere within the upper meter of snow. If you are trying to thread the needle today, beware of that layer.  Some softer slabs will also form as wind speeds slow this afternoon though will probably not be all that reactive due to the tired, old wind blown particles packing fairly tightly. Potential bed surfaces grew substantially in the last several days and are much more continuous, most notably in Center Bowl, below Central and below Yale. Mid snowpack density changes could be the weak layer; don’t you be the trigger on larger wind loaded slopes. Yesterday morning showed extensive sluff piles below steep sections indicating further load on the lower start zones. Remember that upper sections of Lobster Claw and Right Gully have filled in and are maturing into legitimate start zones. Lower Snowfields will remain threatened by natural avalanches from above. Though the current wind slab, like any harder wind slab, isn’t touchy in nature, it could sure propagate a crack a long distance and produce a large avalanche. While widespread natural avalanche activity isn’t really on the radar today, a destructive human triggered avalanche certainly is.

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 840a.m. 2-20-2014. A new advisory will be issued tomorrow.

Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2014-02-20 Print friendly