Avalanche Advisory for Saturday, December 27, 2014

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This advisory expires tonight at 12:00 midnight.

Tuckerman and Huntington Ravines have LOW avalanche danger.  Natural and human triggered avalanches are unlikely except in isolated terrain features.

AVALANCHE PROBLEM: The potential for isolated areas of Wind slab should be remembered today, but generally this should be a remote issue.  Since the thaw and rain on Tuesday and Wednesday we have only picked up a meager amount of new snow.  This may have given us a pocket or two behind some terrain features, but high winds have kept most areas scoured clean.  The water saturated snow from Wednesday has been re-freezing deeper each hour as cold air temperatures remain in place.  This continues to create a bridging eggshell over the snowpack causing any deep weaknesses to be inconsequential. Place your focus on new developing instabilities that may occur on top of the crust during upcoming precipitation events, such as tonight’s snow showers.
WEATHER: Yesterday, very high winds continued to pound the hill, peaking at 112mph (180kph).  Speeds have trended downward and the current winds, gusting to 75mph, are forecasted to continue falling to 30-45mph later today.  Expect sunshine and some clouds to give us a fairly reasonable day in the mountains.  Tonight snow showers will return expected to deliver 1-3″ (2.5-7.5cm) by Sunday morning.  This will be the first snow on the mountain since Thursday’s 0.4″ (1cm).  Winds will also increase once again, exceeding 100mph (160kph) from the W tonight and into tomorrow.  Temperatures will start moving down again, perhaps hitting 0F (-18C) Sunday night and early Monday morning.  Expect a very cold week ahead with temperatures deep into negative F territory.

SNOWPACK: The freewater from Wednesday’s wet event has been freezing from the surface down for about 48 hours. Snow temperatures will continue to fall with cold ambient air in place freezing and bonding round wet grains deeper by the hour. As already mentioned, this creates a bridge over any deeper weaknesses due to its strength.  Additionally, we have thin early season coverage so the freezing upper snowpack is also held in place by freezing around brush, trees, poking cliffbands, and rock anchors.  We’ll watch, as should you, for faceting/recrystalizing that will likely occur this week with very cold air settling in.  However, continued moderate to high wind speeds should keep this process from occurring too rapidly.  In the meantime, the big issue is more the slick surfaces that exist. As discussed yesterday, the current icy snow surface will lend itself more to a bobsled run than arresting a fall with an axe easily.  If a slip does cause a fall, an immediate self arrest is absolutely critical due to the potential for Mach speeds in a blink of an eye.  Unfortunately, history has shown that sliding falls into the rocks below is the most frequent accident when we have slick surface conditions. Microspikes and trekking poles are helpful on very low angle trails approaching the Ravines, but have no place in steep terrain.  Crampons, an ice ax, and the skill to use them effectively are all needed to travel safely on the upper mountain.  Ice climbers should expect the potential for ice dams struggling to hold back water pressure beneath the ice.  This is most common in narrow gullies, but is also common near bulges in more open terrain.  These have a history of causing accidents as their pressure becomes released by a swinging ax placement.  It goes without saying, but I’ll mention it anyway. Expect the Sherburne ski trail to be very challenging with hard rough terrain.

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 6:50 a.m. December 27, 2014. 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

2014-12-27