Avalanche Advisory for Sunday, March 19, 2017

This advisory expires at Midnight.

Huntington and Tuckerman Ravine have LOW avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEMWind slab remains our avalanche problem today. Primarily formed Wednesday night and Thursday, this firm slab exists over much of our terrain, is largest in Sluice, Lip, and Center Bowl, and can be found in pockets of varying size on most aspects. Bonds between this layer and the underlying snow surface have gained strength over the past several days. While resistant to a human trigger, the resulting avalanche could be large. This possibility, albeit unlikely, certainly remains and demands respect in your travel decisions. Where this slab is not present, an old, icy rain crust is the snow surface. It’s darker in appearance and quite hard underfoot making it fairly easy to differentiate from the areas of wind slab. Offering a stable surface to travel on, this crust is certainly hard and also provides good crampon purchase, limited edging ability on skis or snowboard, and a great surface on which to take a long sliding fall.

WEATHER: Yesterday, clear skies, mild temperatures, and low winds allowed many to enjoy a great day of recreating on the mountain. Today will be similar, although it is likely clouds will be more present and may even create occasional snow showers in the afternoon. Winds will start from the SE at 5-20mph and increase in the afternoon to 25-40mph while shifting to the N by the end of today. Currently, the temperature on the Summit is 8F, with highs for the day reaching the mid-teens.

SNOWPACK: After the Tuesday Nor’easter cleared, much of our terrain was left scoured to old surface due to strong E winds. The seven inches (7”) that arrived Wednesday and Thursday came on W winds and has since been treated to strong winds from the NW. The result of this 7” is more of the surface snow being wind slab than old surface. The south wall of Huntington (Odell, South, and Escape Hatch) as well as The Chute, Left Gully, and Hillman’s in Tuckerman have wind slab that is firm (pencil hard) and very wind textured. Some of the higher ends of these gullies are scoured to the old surface, but just the very tops. Gullies with an east-aspect, Central, Sluice, Lip, and Center Bowl, contain the most contiguous and thickest wind slab. This will be firm (pencil to one-finger hard), but slightly less dense than the southern gullies. The upper layer is supportive and providing bridging strength to potential weaknesses beneath, but caution should be exercised when entering or leaving these areas as the edge of the slab will be the thinnest and the area where there is potential to affect the weak layer. Thin spots will also be found around terrain features like cliffs and rocks hidden beneath the snow surface. These areas are modeling the classic example of low probability but high consequence. It is unlikely they will avalanche, but if they do it would be a hard slab that would likely entrain a good amount of snow. The north wall of both ravines contain some of the softest wind slab. The upper reaches of Damnation yesterday had wall-to-wall four-finger (4F) hard snow on top of a fist (F) hard layer. This slab was 50cm deep and was still small enough to considered a pocket, but worth keeping an eye on. Bluebird skies yesterday along with no winds allowed some of the old rain crust surface to soften where exposed. This was not widespread and limited to areas that received the maximum amount of sun possible. With intermittent cloud cover today, we are less likely to see the corn cycle continue.


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 7:40 a.m., Sunday, March 19, 2017. A new advisory will be issued tomorrow.

Ryan Matz/Helon Hoffer, Snow Rangers
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856