Avalanche Advisory for Saturday, March 21, 2015

This advisory expires at midnight.

Tuckerman and Huntington Ravine have Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible.   Evaluate weather, snow and terrain carefully to identify features of concern. Heightened avalanche conditions will develop on specific terrain features later today.

Snow and wind is expected to pick up late in the afternoon which should increase the above ratings very late in the day.  Both Ravines will be at the ceiling of their rating definitions in the afternoon. The ratings above most accurately reflect the recreational daylight period, however this is all based on the expectations that snow accumulations are limited until then. Anticipate avalanche danger to increase, moving towards Considerable, from dinner time towards midnight as snow increases in volume and intensity.

AVALANCHE PROBLEM: We are starting the day with a generally stable snowpack. Firm wind slabs with good stability are the predominate feature of our upper snowpack. Unstable new Wind Slabs will become the primary avalanche problem today. New snow this afternoon on increasing winds will build wind slabs in our start zones which will be reactive to human triggers and will potentially release naturally late this evening. Older Wind Slabs resting on the steepest slopes are the second concern to look out for. Though stubborn, these slabs could potentially crack and fail if you applied the right load in the right spot.

WEATHER: Some snow flurries are falling at the moment with the temperature standing at a relatively balmy 20 F (-7 C) under an overcast sky. The cold front that is arriving today will bring 1-3″ (2.5-7.5 cm) of snow this afternoon with 2-4″ (5-10 cm) overnight followed by upslope showers tomorrow amounting to 1-2″ (2.5-5 cm). Winds are currently light from the west at 20-35 mph (30-55 km/h) but will increase through the day to the 35-50 mph (55-80 km/h) range and hit the 80-100 mph (130-160 km/h) range overnight. Today, winds speeds will be ideal for loading and will also contribute to diminished visibility. Temperatures will fall to around -15 F (-26 C) overnight. The timing of this incoming weather has the potential to spring a trap on the unwary or under prepared! Consider the consequences of delays in your travel plan today!

SNOWPACK: Very firm snow conditions exist throughout the Ravines with a mix of  just barely boot-able and edge-able firm newer wind slabs and more heavily textured snow (sastrugi) in windward areas like Hillman’s, Left Gully, South and Escape Hatch. The smooth pencil hard snow of gullies and slopes with a more southerly and easterly aspect allow passage without crampons but only with extreme care….consider wearing points particularly as new snow covers areas of the icier crust that exists on slopes that have caught sun lately. The firm, newer wind slab is resting on a much older, almost knife hard wind slab and an icier melt freeze crust. Field work in Right Gully, SLuice and Chute yesterday revealed that the firm, newer windslab was surprisingly well bonded with these harder layers below. Clean and smooth but slow and un-energetic Q2 shears broke in the upper wind slab layers rather than on the harder surface beneath. There was no sign of faceting at this interface yet but it is something to keep an eye on as temperatures plummet tomorrow. The firm wind slab in the upper snowpack is very strong and bridging well.

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 8:35 a.m., Saturday, March 21, 2015. A new advisory will be issued tomorrow.

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

2015-03-21