Avalanche Advisory for Sunday, April 2, 2017

This advisory expires at Midnight.

Huntington and Tuckerman Ravines have CONSIDERABLE avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Dangerous avalanches conditions will exist today. Careful snowpack and weather evaluation, cautious route finding and conservative decision making are essential. The only exception to this rating is the Little Headwall, which has LOW avalanche danger. Natural and human triggered avalanches are unlikely.

AVALANCHE PROBLEM: New and currently growing Wind Slab is our primary avalanche problem today. NW wind, sufficient to transport snow that began early this morning, will continue to load lee slopes of a NW wind through today. Yesterday’s Storm Slab, which produced 3 skier triggered avalanches, and one natural, is a secondary problem today. The weak layer consistent across these avalanches will remain today, either below newly formed wind slab or the storm slab remaining in wind-sheltered areas. Every gully in Tuck’s that was skied yesterday avalanched, and untested slopes with slabs increasing in size through the day are likely to follow suit.  Further, summit fog is currently hampering visibility to our upper start zones, so it’s entirely possible for an avalanche to be triggered above you without any visual indication.

 WEATHER: After minimal wind yesterday, we’ve returned to more typical conditions this morning, with NW wind on the summit near 40 mph prevailing since midnight. Wind speed will increase slightly throughout the day and remain from the NW, with gusts to 60 mph or higher. These speeds are certainly sufficient to transport the 12”+ of relatively high density (8-10% water) snow that fell on light E wind late Friday and into Saturday morning. It’s currently 13F on the summit, and today’s high temperature will be near yesterday’s 23F. Lower elevations will see slightly higher temperatures. Cloud cover will diminish slightly through the day, but mostly cloudy conditions are forecast to prevail.

SNOWPACK: Though yesterday’s avalanche activity swept out a few forecast areas, plenty of hangfire remains on the slopes that were tested by foot or ski traffic. Every forecast area that saw traffic, including a couple outside of our forecasted terrain in Gulf of Slides, released an avalanche in the storm slab. Skier’s left fork of Lobster Claw, a couple of hundred feet below the top of Right Gully, and skiers left fork of Hillman’s Highway all saw avalanche activity in the new snow triggered by skiers yesterday. A crown face from a natural avalanche, which was partially reloaded, was also visible yesterday in Center Bowl a few hundred feet below the ice. One takeaway lesson for many folks from this avalanche cycle was that formal stability tests are not a good substitute for classic red flags. Compression tests, extended column tests and other tests do not really work in “shallow” snow, particularly not loose snow with barely enough cohesion to form a slab. Twelve inches of fresh snow within the past 24 hours, ridgetop winds, slopes over 35 degrees, as well as cracking under foot on low consequence test slopes are among the classic indicators that avalanches can occur. Yesterday’s relatively light wind speeds created a storm slab avalanche problem that we don’t often see here and created unfamiliar conditions for even experienced avalanche terrain travelers. Today’s wind slabs will be much more familiar to everyone. The size of today’s avalanches will be a result of a complex formula that includes density of available snow on the ground, direction and duration of loading wind speed, and the breaking point of existing weak layers. Today we have the potential for larger avalanches that could break above you on the slope, either from your own weight, from increased load of new wind transport, or another trigger. These avalanches will also run much further into flat terrain than yesterday’s soft slabs so think twice before heading out into the runouts of avalanche paths in either ravine.

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 Harvard Cabin.

Posted 8:00 a.m., Sunday, April 2, 2017. A new advisory will be issued tomorrow.

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

2017-04-02