Avalanche Advisory for Wednesday, March 18, 2015

This advisory expires at midnight.

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

All forecast areas in Huntington Ravine have MODERATE avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Evaluate snow and terrain carefully to identify features of concern.

 AVALANCHE PROBLEM:  Wind velocities over the past 12 hours have reached past the century mark and scoured many of our start zones especially in higher elevation areas in Huntington.  Large but stubborn Wind Slabs in other areas protected from the NNW and NW wind are the primary concern. Look for these slabs lower in our slopes and gullies such as the approach to climbs in Huntington, the Lower Snowfields and mid slope in the Considerable rated terrain in Tuckerman. Another trace to 2” (TR to 5cm) of snow on somewhat diminishing winds is forecast later today. This new snow has the potential to create more wind slabs higher in start zones in the more typical places and add load to existing wind slabs.

WEATHER: Low visibility due to summit fog and continued blowing snow will create a significant challenge to snow and terrain assessment to anyone braving the wind and cold. Identifying your position relative to an avalanche path will be difficult, to put it mildly, so travel in the floor of either Ravine, and particularly Tuckerman’s, is probably not the best use of your time today. Even if you know the terrain intimately, wind velocity and cold will make travel near treeline a significant challenge with a razor’s edge safety margin. High temperatures around -15F (-26C) and winds gusting to 120 mph (190 km/h) will again delay the onset of spring skiing conditions.

SNOWPACK:  On Sunday and Monday, relatively small skier triggered avalanches in Hillmans (Sunday, R2) and Right Gully (Monday, R3) were a good reminder that spring skiing weather and good snow stability do not rely on the calendar to arrive. These wind slab avalanches failed on the interface between harder and softer wind slabs that developed over the weekend. This interface was thin but failed cleanly and easily in stability tests. Furthermore, a melt freeze crust from last Tuesday/Wednesday shelters another weak layer of snow in the upper snowpack. Though discontinuous, this melt freeze layer forms the upper slice of bread in a weak layer sandwich with the old, hard slab beneath. This layer of early facets is worth keeping in the back of your mind since it may be a player in areas where it still exists. It was swept out and no doubt contributed a volume of snow to the avalanche in Hillmans.

It is important to remember that hard slabs like the ones developing from today’s wind can be deceptive in that they may appear stable due to their firmness. However, this firmness can also be understood as brittleness, so this type of slab can crack a good distance on a steep slope as the slab weakens due to warming or stressed by an increasing load such as more slabs or skier/climber weight in the right spot.

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 8:05 a.m. March 18, 2015. A new advisory will be issued tomorrow.

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

2015-03-18 print friendly