Avalanche Advisory for Sunday, March 12, 2017

This advisory expires at Midnight.

Huntington Ravine has 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 and Chute have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Lobster Claw, Right Gully, Left Gully, Hillman’s Highway, and the Lower Snowfields have Low avalanche danger. Natural and human-triggered avalanches are unlikely. The Little Headwall is not forecast due to lack of snow.

AVALANCHE PROBLEM: Firm Wind Slab developed from Friday’s snow and strong WNW winds on Saturday. Today, continued wind loading on decreasing winds will deposit remaining snow available for transport onto these areas, but should not be enough to increase the hazard for the day. Slopes in lee areas of WNW winds have the largest pockets of wind slab. These are identifiable by a smooth appearance and cleaner looking snow when compared next to the gray, refrozen old surface. In Tuckerman, wind slab connects Sluice through the Chute, creating the potential for a larger avalanche when compared to pockets in Low rated areas. Strong winds are creating small particles of snow that are finding a way to stick in many places to the textured old surface. Because of this, many areas which are smooth and would appear to have new wind slab are actually old surface that is just hidden under a skim of broken snow grains. This should highlight the importance of continued snowpack evaluation while moving around in terrain today.

WEATHER: After 5.8” of snow on Friday, strong winds and cold temperatures dominated Saturday. WNW winds blew in the 70-100mph range all day yesterday with temperatures bottoming out at -35F. Today, high pressure is approaching from the west and may allow for some clearing during the day. This will compete with moisture in the air creating some summit fog as well as the continued winds blowing loose snow. Up to an inch of snow may arrive this afternoon before skies clear overnight.

SNOWPACK: Prior to a week ago, our snowpack went through several melt/freeze cycles creating a firm base layer with an icy surface. Over the past week, cold temperatures prevented significant snow loss and several inches of snow has created scattered areas of wind slab. Before the wind really picked up Friday evening, this new snow was creating soft slab. As winds increased and began scouring in places, this 5.8” of snow created a mix of exposed old surface and areas of firm wind slab. This morning, one-finger hard slabs were encountered at the base of the Ravines with likely firmer slabs at higher elevations. In areas like the Lip of Tuckerman, these firm slabs sit on top of the softer slab that formed on Friday, creating a weak layer. With this layering in mind, add the fact that yesterday’s slab will be firm and strong. The edge of these slabs can be thin and are often the place where a person can impact the soft layer below, something to keep in mind when moving around on changing snow surfaces.

 

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 8:20 a.m., Sunday, March 12, 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

2017-03-12