Avalanche Advisory for Thursday, March 12, 2015

This advisory expires at Midnight.

Tuckerman and Huntington Ravines have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely.  Dangerous avalanches conditions exist.  Careful snowpack evaluation and conservative decision making is essential. The only exception to this is the Little Headwall which has Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible.

AVALANCHE PROBLEM: New Wind Slabs are the primary concern today.  Dry loose sluffing will be problem #2 in very steep terrain. Down at Hermit Lake about 3-3.5” of new snow, in addition to more forecasted today, will create unstable new soft and hard wind slabs through the majority of daylight hours. This will load on icy crusts that developed during very warm weather earlier in the week.  Poor visibility in avalanche terrain will make route finding very difficult, exposing you to threats from above.  Be conservative in your mountain travels.

WEATHER: A cold front through the region gave us a quick shot of cold dry snow this morning.  Wind has affected a very accurate reading, but 3” to 3.5” (7.5-9cm) is a good bet based on sampling from our snow plots and multiple trail locations. This precipitation was transported on a very strong NW wind, which will continue today from 70-90 mph (112-144kph), perhaps gusting to 100 (160kph).  1-3” (2.5-7.5cm) of snow is forecasted for today with temperatures falling to -10F (-23C).

SNOWPACK: Yesterday, started warm with the bottom of avalanche runout paths around the freezing mark at (0C).  Start zones, up higher, were several degrees cooler before the slow mercury drop through the day brought them lower.  The temperature drop was associated with very poor visibility and very high winds close to 100mph.  Any wet snow that existed froze.  This became the new potential bed surface for avalanche issues today.  I would expect a final total between 4-5” (10-12.5cm) of cold snow falling in ambient air temperatures around 10F to 0F (-10C to -18C). This should create cold soft to hard slabs depending on location.  In strong protected locations in the lee of NW winds, such as in the Lip and under the Tuckerman Headwall, a softer slab will be generated.  In locales more subject to the effects of strong wind, such as low in the Chute, a harder slab will be created.  High winds will undoubtedly create a wide variety of conditions, so anticipate changes as you travel.  Don’t be surprised to initially be on scoured old surface, which may be stable, only to get into large areas of instability as the terrain and degree of sheltering changes.  The very poor visibility today will make it extremely difficult to make good route choices and decisions.  The weather that the mountain is delivering today will make it challenging to make fully informed decisions based on the inability to accurately assess the terrain.  Expect the possibility of natural avalanches to occur from above, particularly in steep terrain.  In very steep terrain, such as in many of the Huntington gullies, anticipate frequent sluffing off of steep water ice piling into new slab at the base of steps and bulges.

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 8:20 a.m. March 12, 2015. A new advisory will be issued tomorrow.

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

2015-03-12