Avalanche Advisory for Monday, March 13, 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. The Little Headwall is not forecast due to a lack of snow.

AVALANCHE PROBLEM: Wind Slab is creating the avalanche hazard today. Today, the danger will remain constant as the forecast weather will not have an impact on the areas of concern or the snowpack as a whole. The largest wind slab in our terrain currently sits just under the rollover of the Tuckerman Headwall with the largest pocket existing in the Lip. This can be identified from afar by its smooth appearance and cleanness when compared to the dirty looking, textured old surface. This old surface is firm and will create the potential for long, sliding falls, something to keep in mind when moving around the mountain.

WEATHER: After a cold and windy weekend, this is a great morning to be in the hills. Steady WNW winds blasted the mountain all weekend. Saturday saw speeds in the 70-90mph range with a slight decrease to the 40-60mph range on Sunday. Overnight, winds shifted to the NW and just now to the W where they should remain for the day, decreasing further to 15-30mph. The last observed snowfall was Friday night at midnight. High pressure this morning cleared the sky and is allowing temperatures to creep near 0F. With the approaching storm and low pressure system, clouds should start to develop in the afternoon as the wind shifts to the S. This may bring a trace of snow, likely occurring after dark.

SNOWPACK: Thanks to the strong wind over the weekend, the majority of the snowpack in avalanche terrain is scoured clean of new snow. This is particularly true in Huntington. Small, isolated pockets of wind slab linger behind terrain features, but these will be easy to avoid by staying on old surface. While many areas of Tuckerman are also scoured, several places saw snow deposited in lee areas. The Chute, Center Bowl and Sluice are displaying pockets of this smooth surface, but these forecast areas are also showing scoured surface that will offer ways to avoid the wind slab. Looking at the Lip, the wind slab (smooth, clean snow) is wall-to-wall at the rollover, making this forecast zone hard to navigate without passing through the avalanche problem. Much of the snow that fell on Friday arrived before winds increased. This allowed for a softer layer to develop that is now sandwiched between the bed surface and the firm wind slab in question today. As the wind slab formed from hurricane force winds that lasted for over 24 hours, the tensile strength of this layer will be very high, bridging the weak layer beneath and creating a slab that will likely be unreactive to human-triggers.

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 8:15 a.m., Monday, March 13, 2017. A new advisory will be issued tomorrow.
Helon Hoffer, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2017-03-13