Avalanche Advisory for Friday, January 20, 2017

This advisory expires at Midnight.

Huntington Ravine has MODERATE avalanche danger. All forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible.

 Tuckerman Ravine has MODERATE and LOW avalanche danger. Sluice, Lip, Center Bowl, Chute, Left and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Lobster Claw and Right Gully have Low avalanche danger. Natural and human-triggered avalanches are unlikely. Heightened avalanche conditions exist today. Evaluate snow and terrain carefully.

AVALANCHE PROBLEM: Wet slabs and loose-wet avalanches will compete for your attention as today. Rising temperatures through the night coupled with sunshine, light winds and warm air temperatures will reduce the strength of our snowpack through the day. Areas of greatest concern are the fan shaped deposits of sluff debris that exist beneath steep terrain in the most easterly facing aspects and beneath steep pitches. These areas as well as large expanses of yesterday’s wind slabs will be capable of producing the largest avalanches. Sticking to the old, firm (and edgeable) surface will reduce your risk of triggering one of these slabs. Loose-wet sluffs could generate some force and enough mass to push you someplace you don’t want to go or to be the trigger for another slab avalanche below.

WEATHER: An inversion is in place currently with 27F at Pinkham, 28F at the summit and 22F at Hermit Lake. Wind is from the NNW at 22mph at the summit and is forecast to shift west and drop to 5-20 mph. Temperatures today will reach up into the mid-30’s F this afternoon on the summit…warmer in the Ravines. Expect aspects facing the sun to heat up first and probably pretty early. The low wind speeds will allow the sun to warm the snowpack quickly.

SNOWPACK: Rapid warming of the snowpack is one of the red flags that students learn about in entry level avalanche classes. Lots of clues indicate that the warming process is occurring such as rime and snow falling off of trees, surface snow that easily forms a snowball and snow that forms pinwheels when rolled downhill. These are all great clues that avalanche danger may be increasing. The most obvious clue that any type of snow instability is emerging is recent avalanche activity. Waiting for that clue to show itself today would be a bad idea. Wet slab avalanches are dangerous and our early season snowpack, with so many rocks, cliffs and trees showing, makes them even more so. Field time in Right Gully, lower Sluice and Chute revealed a weak interface at and just above the old refrozen bed surface. Four finger plus hardness wind slabs 20-50 cm deep are fairly widespread. A night of a decent temperature gradient driving some early faceting combined with weakening of the upper surface slab by the warmth is probably enough to make these slabs more reactive to human-triggering. The thicker slabs of sluff deposits are much more unpredictable and should be treated with some respect. Hillman’s and Left Gully have too much slab in the mid-sections around the fork and choke point, respectively, to be rated Low but are in the lower end of moderate compared to Sluice through Chute.

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 8:24a.m., Friday, January 20, 2017. 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

2017-01-20