Avalanche Advisory for Wednesday, March 14, 2018

Huntington Ravine has High and Considerable avalanche danger. Central Gully has High avalanche danger. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. All other forecast areas have Considerable avalanche danger. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential.

 Tuckerman Ravine has High and Considerable avalanche danger. Sluice, Lip, and Center Bowl has High avalanche danger. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. All other forecast areas have Considerable avalanche danger. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. The Little Headwall is the exception with Moderate avalanche danger.

 AVALANCHE PROBLEM: Wind slab formed from northerly wind will be the primary avalanche problem this morning before wind shifts NW and begins to build new and potentially larger slabs late today. These new layers will all be very sensitive, likely to avalanche naturally and very likely to be human triggered in High rated areas. If that’s not enough to keep you out of the terrain, storm slabs and dry loose sluffing will be secondary problems forming from the snow currently falling on light wind. This number of avalanche problems is compounded by deeper and potentially unstable slabs formed late last week in much of the terrain. You’re likely to trigger an avalanche in essentially all forecast areas today, and avalanches could be quite large. It’s a great day to enjoy the powder away from avalanche terrain or at the ski area!

 WEATHER: The Nor’Easter arriving yesterday morning has so far brought 16 inches of snow to Hermit Lake, with 9.5 inches recorded on the summit. Snowfall continues currently. Summit wind speed held in the 40-50 mph range while shifting from NE to N during the heaviest snowfall periods which occurred yesterday evening. Wind speeds have diminished since midnight as direction alternated between N and NE to the current 11 mph out of the N on the summit. Snowfall should continue today and be heaviest this morning, with forecasts suggesting another 6-11 inches of accumulation. Summit wind will shift NW and steadily increase to the 30-45 mph range by this evening, with a high temperature in the upper teens and summits in the clouds all day. The big player tomorrow will be NW wind between 50-70 mph holding through the day as snowfall tapers to minimal amounts.

SNOWPACK: The significant snowfall which continues now is rapidly changing our upper snowpack. The northerly wind late yesterday blew with speeds likely to build soft and very sensitive slabs in lee and cross loaded terrain. Particularly sheltered areas could exhibit barely cohesive snow which acts more like a storm slab. This new snow continues to fall and will be transported by wind in greater amounts late today as NW winds approach 50 mph and move snow from our primary fetch zones into the Ravines. Several layers of varying hardness though relatively soft (1F-4F) wind slab formed since late last week lie on the old icy snow surface that previously dominated our terrain. These older wind slabs have gained some stability but shouldn’t be considered stable in our steep terrain. They still could release in a step-down fashion from an avalanche initiating closer to the surface or from continuing added weight of new snow. The exception to this are the few areas that were scoured to the old icy snow prior to this storm, especially upper Left Gully in Tuckerman and Odell Gully in Huntington. Additionally, significant graupel pooling Sunday, in isolated pockets primarily below water ice, is likely to act as a weak layer in these select locations. It’s safe to say that this complexity in our recently formed upper snowpack will challenge your ability to assess it.

 The Harvard Cabin will be open all nights this week.

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 7:40 a.m., Wednesday, March 14, 2018. A new advisory will be issued tomorrow.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2018-03-14