Avalanche Advisory for Monday, February 15, 2016

Tuckerman Ravine has MODERATE and LOW avalanche danger.  Sluice, Lip, Center Bowl, and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Right Gully, Left Gully and Hillman’s Highway have Low avalanche danger. Natural avalanches and human-triggered avalanches are unlikely. Lobster Claw, Lower Snowfields, and the Little Headwall are not posted due to lack of snow cover.

Huntington Ravine has MODERATE and LOW avalanche danger. Central, Pinnacle, Odell, and South have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. North, Damnation, Yale and Escape Hatch have Low avalanche danger. Natural and human-triggered avalanches are unlikely. Exercise caution in these areas and expect the potential for isolated patches of instability.

AVALANCHE PROBLEM: Wind slab is the primary avalanche problem today. The weak layer of soft snow responsible for our last avalanche cycle Thursday night has been preserved by very cold temperatures since its development. Overlying firm slabs exist in many areas of our terrain and may appear to be nothing but a supportable surface that yields more easily to your boot than the icy melt/freeze crust nearby. Don’t be lulled into thinking that these hard slabs won’t fracture due to being so firm. Their ability to fracture will be dependent on a complex interplay between their thickness and position in the terrain and the thickness of the weak layer of soft snow beneath and the slabs ability to span over it. Traveling one at a time, staying out of the runout as much as possible and generally practicing safe travel techniques are recommended today. Though natural avalanches are unlikely the potential for a skier or climber to trigger an avalanche is certainly possible.

WEATHER: A strong inversion this morning is a good indicator of relaxed winds and limited mixing at lower elevations. Temperatures will continue to climb today to the mid-teens F on the summit as winds shift to the southwest and begin to ramp up again this afternoon as a storm approaches. Expect southwest winds to be blowing in the 50-70 mph range near sundown. The low pressure system will start out cold enough to produce snow this evening and overnight before transitioning through the spectrum of mixed precipitation tomorrow. Expect elevated avalanche danger tomorrow.

 SNOWPACK:  Field time yesterday confirmed that our wind slab issues still exist and remain an issue following yesterday’s minor wind-loading and continued cold temperatures. A veil of snow hung over the Alpine Garden for most of the day. Cold temperatures have not allowed the existing wind slabs to settle and bond and is probably driving the temperature/vapor gradient needed to cause some faceting near the buried crust. As stated above, both firm and newer, softer slabs rest on a weak layer of lower density (F hardness) snow that can serve as the weak layer in the avalanche recipe. You’ll also find areas scoured down to the February 3rd-4th melt-freeze crust in both Ravines which require crampons to penetrate. See our post from yesterday’s field time for more.

The Lion Head Winter Route is open and the recommended east-side route to the summit that avoids avalanche terrain. The John Sherburne Ski Trail is in a typical mid-winter state with packed snow and some bare patches of ice.

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 7:55a.m., February 15, 2016. A new advisory will be issued tomorrow.

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

2016-02-15