Avalanche Advisory for Sunday, December 31, 2017

Huntington Ravine has MODERATE and LOW avalanche danger. Central, Pinnacle, Odell, South, and Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully, identify features of concern. North, Damnation, and Yale gullies have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

Tuckerman Ravine has MODERATE and LOW avalanche danger. Sluice, Lip, Center Bowl, Chute, Left, and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully, identify features of concern. Lobster Claw, Right Gully, Lower Snowfields, and the Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

 AVALANCHE PROBLEM: Variability in our upper snowpack keeps ratings at Moderate for much of the terrain today, with wind slab continuing as our primary concern. We expect greatest instability in the smooth slabs commonly existing between ½ and ¾ of the way up much of our terrain. Our upper start zones are largely wind hammered to a firm and textured snow surface which would be hard pressed to produce an avalanche. Thin areas of the softest and smoothest pockets of wind slab have the greatest potential to produce a human triggered avalanche today. Low rated areas will tend to offer more options to avoid today’s avalanche problem. Don’t become complacent due to firm feeling snow. Dig and probe before committing to travel on wind slabs.

 WEATHER: High pressure continues to allow arctic air to dominate our area. Temperatures in the negative 20’s F are currently combining with wind gusting over 80 mph on the summit. No significant slab building snow is being transported. We should see quite consistent weather today through tomorrow, with summit temperatures in the teens below zero and NW wind around 60 mph. Partial cloud cover and no measurable precipitation is expected. A break in these frigid conditions will hopefully occur later in the week. A potential low pressure system Thursday into Friday could bring temperatures well above zero and new snow.

SNOWPACK: Arctic temperatures slow stabilization at best and also have the potential to create facets which can act as a weak layer. While bonds beneath surface slabs are likely growing in some areas, potential exists for facet growth and weakening of bonds in other areas. The crust formed days before our Christmas storm continues to be a player where beneath the surface and not wiped out by avalanches. In short, the upper portion of our snowpack has high variability. This variability can be difficult to visually discern except for areas where the old crust is present at the surface. As a result we have not lowered ratings since yesterday. If you brave the chilling conditions, be sure to consider the consequences of even the smallest avalanche or any accident.

Please Remember:
• Safe travel in avalanche terrain requires training and experience. This bulletin 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 Harvard Cabin.
• Posted 7:40 a.m., Sunday, December 31, 2017. A new advisory will be issued tomorrow.

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

2017-12-31