Avalanche Advisory for Wednesday, March 23, 2016

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Moderate and Low avalanche danger. The Sluice, Lip, Center Bowl, Chute, Left Gully, and Hillman’s have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Right Gully has Low avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

Huntington Ravine Moderate and Low avalanche danger. Central Gully has Moderate avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. All other areas have Low avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

AVALANCHE PROBLEM: Wind slab is going to be the #1 problem again today, although the amount of snow we get this morning will determine whether we are dealing with primarily older slabs or if we also have new slab problems developing today. The worst stability in either old or new slab rated at Moderate will be found in locations from Sluice through Chute in Tuckerman and Central in Huntington. Other areas rated with the same rating should be treated with caution as well, as you may find smaller areas of very touchy snow or larger expanses of more stubborn and difficult-to-trigger slab. Expect isolated pockets of instability in Low-rated areas such as Right Gully or much of Huntington. New snow will be increasing the overall avalanche hazard!

WEATHER: While the summit recorded 3.5” Monday night, lower elevations on the mountain weren’t so fortunate. We saw only 1” that morning at Hermit Lake and our field time in Tucks led us to believe that even Bigelow Lawn only saw a light snowfall. Last night, snow began around midnight on WSW winds which are diminishing gradually over time. For today, 1-2” of new snow is forecast. Temperatures around ravine elevations may flirt with heading above freezing, but with cloudy skies I don’t expect much in the way of heating.

SNOWPACK: As is often the case, spatial variability is quite strong right now. There are a mix of surfaces, including scratchy hard crust, e.g. in much of Right Gully; heavily wind-effected snow, e.g. up high above the steepest pitches of Chute and Center Bowl; and recently formed 1F+ (1 finger hardness) slab, which is found in pockets scattered throughout the ravines and larger sections of the Lip, Center Bowl, and Central Gully. Some locations also have sun crusts and/or melt-freeze crusts in the upper portions, e.g. in Sluice’s midsection. The most concerning situation is where smooth new wind slabs have built over the March 16 rain crust or over sun crusts on S-facing slopes. Weak snow sits just above the rain crust, with an overlying slab of variable thickness comprised of a couple weak interfaces. In one pit yesterday, the surface slab yielded CT0 and CT8 compression test scores in the upper 1 ft. of snowpack, while the entire slab failed at ECTP14 and ECTP21 above the rain crust. The most significant finding, which shouldn’t be much of a surprise, is that the snow was more stable in test locations with thicker, more wind-effected slab.

Today, new snow will be adding additional load above existing weak layers, making them more susceptible to human-triggered releases. If we get more than the forecasted 2” and winds stay strong, we may exceed the day’s hazard rating. In the large cone of windblown snow in the lower part of Chute, as well as under the headwall ice, in much of the Lip, and in the open midsection of Sluice are where this would be most likely. Don’t be lulled into complacency if your routes involve smaller snowfields. If an area has anything other than the hard icy crust, expect it to be unstable until you can determine otherwise.

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 8:15a.m., Wednesday, March 23, 2016. A new advisory will be issued tomorrow.

Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2716