Avalanche Advisory for Tuesday, January 20, 2015

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Considerable, Moderate, and Low avalanche danger. Right Gully, Sluice, Lip, Center Bowl, Chute, Left Gully, and Hillman’s Highway have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Lobster Claw has Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanche are possible. Lower Snowfield and Little Headwall have Low avalanche danger. In these areas, natural and human-triggered avalanches are unlikely, but watch for unstable snow in isolated terrain features.

Huntington Ravine has Moderate and Low avalanche danger. Central and Pinnacle Gullies have Moderate danger. Natural avalanches are unlikely and human-triggered avalanches are possible. All other forecast areas have Low avalanche danger. Natural and human-triggered avalanches are unlikely; however, watch for unstable snow in isolated terrain features.

AVALANCHE PROBLEM: Wind slabs are the greatest threats today, as well as slabs formed from piles of recent sluffing found near the transitions from steep terrain to slightly less steep terrain. Examples of where you may see the sluff-slabs are at the base of Pinnacle Gully or beneath the ice in the Sluice. In fact, as I write this, the slab beneath the Sluice just avalanched. That’s “bulls-eye” information about the existence of stability problems. Wind slabs can be found in a variety of locations. There is currently a large amount of snow being blown around the tops of both ravines; you’ll want to know the extent to which this is contributing to development of unstable slabs.

WEATHER: A storm Sunday night and Monday morning brought a lot of moisture to the mountains. At Hermit Lake we measured 2.3” (5.9cm) of water equivalent, which was a bit more than forecast. The type of precipitation that fell varied greatly at different elevations. A stout ice crust is found at elevations around Harvard Cabin, from Hermit Lake up to Lion Head the crust is more like refrozen ice pellets, and above Lion Head precip fell as mostly heavy dense snow. It seems as though the dividing line between all snow and mixed precip was somewhere around the tops of the ravines, so the surfaces in the ravines themselves did not escape without some mixing and crust formation. Also, an inch or two of (2.5-5cm) of rimed stellars fell mid-day yesterday. Today’s wind at 70-90mph with higher gusts will continue to fetch this snow from the alpine zone and redistribute it around the mountain.

SNOWPACK: Much of the terrain in locations rated Low already shows signs of being scoured and hammered by strong winds. In these areas, keep an eye out for protected pockets that may have held onto wind-loaded snow and formed smaller unstable slabs.

In the Considerable rated areas, you may find that a lot of the snow is encapsulated in the crust. Where this is the surface condition, the snow will be relatively stable, although in the thinner spots it is possible that you’ll encounter some of the worst breakable crust imaginable. What you need to be alert for are the locations that held onto snow as it loaded into avalanche start zones. We found this yesterday at the top gullies along the Lion Head Trail, where soft slabs over 1m deep had been able to form. Additional loading is definitely taking place today, at least in protected locations.

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 9:00 a.m. January 20, 2015. A new advisory will be issued tomorrow.

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