Avalanche Advisory for Friday, February 19, 2016

All forecast areas of Tuckerman and Huntington Ravines have LOW avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for isolated pockets of snow in strongly protected lee areas.

AVALANCHE PROBLEM: Recent rain on the summit a few days ago, with 12 hours above freezing, has since drained and refrozen leaving a widespread crust.  Therefore, long sliding falls, lingering ice dams, melt-channels, and undermined ice are more of a concern than avalanches right now.  However, a new avalanche problem will develop very late tonight into tomorrow.  See more details below in the Weather and Snowpack discussion.

WEATHER: Over the past 24 hours the summit as had a slow steady crawl from -4F (-20C) yesterday, to about +10F (-12C) degrees this morning. Very light winds overnight allowed cold air to settle and pool at the base of the mountain, creating an inversion.  This will change today as winds increase forcing air to mix. It will be a fairly pleasant day for mountain travel with a beautifully clear alpine glow morning, slowly being overtaken by high thickening clouds during the second half of the day.  Very late tonight and into tomorrow morning snow, falling heavy at times, will begin delivering 1-3″ (2.5-7.5cm) by dawn.  This will be followed by additional snowfall through the morning hours on Saturday for another 1-3″ (2.5-7.5cm).   An upslope air and moisture regime will drive more snow showers Saturday night. Although a wide total accumulation window of 3-8″ (7.5-20cm) is anticipated by the middle of weekend, the exact amounts will play the dominate role in the exact avalanche danger rating. But you can expect it to be elevated with a Moderate to Considerable rating being likely.  This precipitation will be delivered on an increasing wind from the SW and W gusting to hurricane force tonight, on Saturday, and again on Saturday night.

SNOWPACK: We expect another cold clear evening last night to drive faceting in our upper snowpack beneath the surface crust.  The warmth driven into the snowpack by rain and warm temperatures on Tuesday has been the perpetrator, along with the current cold air, for a wide temperature gradient.  You can expect this to force vapor movement allowing facet development beneath the crust.  The crust, being less permeable than snow below, can act as a barrier and heat sink, creating a more aggressive facet building scenario on it’s underbelly.  It will appear to be cannibalizing the water in the crust, eroding it, allowing it to be more breakable under foot.  There is a chance that tomorrow’s new Wind Slab development could step down through this crust if we see new direct action avalanche activity.  Expect the bonding of new snow, and slab in the deposition of SW and W winds, to be poor with the cold slick surface crust.  This reality will be one of the main drivers in what we select for the most appropriate avalanche danger rating for tomorrow.  The poor adhesion will increase the likelihood of failure in shear with the bedsurface. Likelihood, along with size and distribution are the factors that play into the danger selection.  Please be sure to check the avalanche advisory on Saturday morning for more details, but be ready for new wind slabs.

The John Sherburne Ski Trail has long sections of water ice.  Although the hues of blue, yellow, grey, clear, and a cloudy white are beautiful for the photographer they are less pleasurable for the skier. A few waterbars are still flowing and bare at lower elevations.

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 7:50a.m., February 19, 2016. A new advisory will be issued tomorrow.

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