Avalanche Advisory for Thursday, April 13, 2017

This advisory expires at Midnight.

Huntington and Tuckerman Ravines have LOW avalanche danger. Natural and human-triggered avalanches are unlikely. The Little Headwall is now a waterfall with open holes and thin snow bridges above.

AVALANCHE PROBLEM: Recent rain and meltwater have drained through our snowpack during the past 12 hours or so as freezing temperatures bring stability to the snowpack. This limits our avalanche concerns today to minor loose-wet sluffing but only if the surface snow heats up enough this afternoon. Of greater concern today are the typical spring hazards that occur this time of year. As the freeze-thaw cycle continues, beware of the mechanical action that this cycle brings. Freezing water acts as a lever on rocks and sunshine spawns rock and ice fall. The thinly bridged and open holes in the Lip and other areas which opened after the prolonged thaw define the term low probability/high consequence, so think twice before dropping into the Lip. Long sliding falls on firm and icy slopes will be a threat as well so don’t forget your crampons and have an alternate plan should spring threats on your planned route rise to an unacceptable level.

WEATHER: The summit received a little over a quarter inch of rain yesterday morning and saw temperatures rise to around 41F after Tuesday and Wednesday when temperatures reached 50F. Temperatures dipped below freezing around 6pm yesterday and now sit at 18F. The summits will be in and out of the clouds today with a threat of scattered snow or rain showers.  A high temperature in the mid to upper 20’s on the summit this afternoon may allow softening of surface snow but that will depend on the absence of cloud cover and cooling winds. Wind is currently from the WNW at 60 mph but is expected to diminish to the 40-55 mph range from the NW this afternoon.

Rain and warm temperatures advanced the spring hazards of undermined snow, waterfall blowouts and icefall and reduced avalanche concerns within our snowpack. Be aware of the following hazards and more today and through the upcoming weekend:

  • Long sliding falls – Crampons are highly recommended in steep terrain. Snowshoes and microspikes are no substitute. Expect a variable snowpack due to rain falling on a mostly firm surface with little boot penetration. Arresting a fall on an icy 30+ degree slope can be practically impossible, even with an ice axe. Refrozen snow and this sliding fall hazard come and go with surprisingly minor fluctuations in temperature, wind and cloud cover.
  • Crevasses or glide cracks, moats and waterfall holes – Warm water flowing under the snow pack creates holes and thin spots in surface that are deep enough to injure or kill you. New snow can drift and obscure the openings.

The Sherburne Ski Trail remains open to the parking lot and is a great consolation prize on days like today when the freeze/thaw cycle make steeper objectives questionable. Snow and ice climbs remain in reasonable condition though many were damaged by the recent thaw. Rock and icefall hazards are often driven by aspect and exposure to sun. The Harvard Cabin is closed for the season. We will continue posting advisories there as long as it is logistically feasible or until the ice melts out and we move to a General Bulletin.

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 caretaker at Hermit Lake Shelters.

Posted  7:30 a.m., Thursday, April 13, 2017. A new advisory will be issued tomorrow.

Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2017-04-13