Avalanche Advisory for Saturday, December 30, 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. 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: Firm and generally stubborn wind slabs are the primary avalanche problem today. These firm slabs will have good bridging strength in lots of areas but realize that thin spots, convexities and other trigger points may still be lurking.  Evaluate snow and terrain carefully as you move around the terrain today. Recent avalanche activity in much of our terrain has swept out the ice crust built from the rain event last weekend but lower angled areas which didn’t avalanche may still hold this potentially problematic layer. You’ll find firm (1F) but mostly smooth slabs in most of our terrain that hasn’t seen the scouring or sastrugi building action of the wind near the ridgetops. Low rated areas have fewer areas of concern and provide more terrain opportunities to avoid them.

WEATHER: Yesterday brought a respite of sorts from the bitter cold at higher elevations, as a temperature inversion allowed the mercury to peak at 7F on the summit and creep into the low teens at Hermit Lake. Temperatures dropped to the teens below zero last night and should stay below zero today. NW wind around 30 mph on the summit could increase to around 50 mph tonight. We will see intermittent cloud cover with a chance of a trace of snowfall. Temperature will drop to around 20 below tonight on the summit and rise only a little tomorrow. Expect increasing wind speeds to compound tomorrow’s frigid conditions.

SNOWPACK: High winds mid-week caused a wide-spread avalanche cycle in the steep terrain of our forecast area, ultimately creating rugged and relatively hard to trigger wind slabs. There are plenty of thin spots in these firm (1F) slabs due to varying thicknesses so human-triggered avalanches remain possible in many areas. Evaluate snow and terrain carefully to identify poor bonding to the ice crust or possibly early faceting. The previous avalanche cycle in our steep terrain cleaned out big sections of this ice crust in some areas like below the ice in the Lip and below the choke in Left Gully but some areas of the crust may remain. An observer in the Ammonoosuc Ravine reported propagation potential on early facets in one stability test (with no ice crust in the pit) and another observer reports that most of the Gulf of Slides did not avalanche in the widespread mid-week cycle. This is a pertinent fact pointing to the possibility of the ice crust with soft (4F-F) snow lurking in large portions of those gullies.  Dig and probe frequently and recognize that cold temperatures and crusts create a dynamic snowpack that could become reactive to human triggers.

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 7:45 a.m., Saturday, December 30, 2017. 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

2017-12-30