Avalanche Advisory for Sunday, February 18, 2018

Huntington and Tuckerman Ravines have CONSIDERABLE avalanche danger. All forecast areas have Considerable avalanche danger. Large avalanches in specific areas and small avalanches in many areas are possible. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential.

AVALANCHE PROBLEM: Wind Slabs that will continue to develop through the day are our primary avalanche problem. Avalanche danger will increase through this afternoon as wind builds our several inches of new snow into much thicker slabs. Increasing wind speeds mean than snow deposited will be generally more dense over less dense snow and therefore be increasingly sensitive to a trigger. Natural avalanches will be possible and human triggered avalanches will be likely. Dry loose sluffs which could knock you off your feet, initiated naturally or by a human, should also be on your radar in our steep terrain. We still have relatively thin snow coverage in much of our terrain, particularly Huntington Ravine. This means that many hazards in the runout of our avalanche paths elevate the consequences of even a small avalanche. Consider the rocks, vegetation, and terrain traps which may be below you if you choose to travel in avalanche terrain today. Also remember that though avalanches typically occur on slopes steeper than 30 degrees, they can run well into flat areas like the floor of Tuckerman Ravine.

 WEATHER: New snow overnight is currently tapering off as wind increases and shifts NW. Mixed snowfall totals and accumulation on the ground lead us to approximate 3” of new snow in our terrain. This morning could bring another trace to 1” with no precipitation expected later today. New snow density at Hermit Lake is 6.9%. SW shifting to W summit wind of around 40 mph accompanied the bulk of precipitation. Wind has shifted NW this morning and should increase with a peak in the 50-60 mph range early this afternoon. Temperature on the summit will hover around 10F. Tomorrow should bring warmer temperatures ahead of a weather system arriving late in the day that could bring mixed precipitation.

SNOWPACK: The wind slabs that are currently forming lie on a mixed surface of icy refrozen snow and areas of wind slab formed early yesterday. Snow deposited Friday night into yesterday morning formed many pockets of wind slab that were largest in areas like the Sluice and Lip of Tuckerman Ravine and smoothed the icy snow surface with a thin layer of snow in areas with lesser slab development. This means that today’s newly forming slabs will have a smooth bed surface and avalanches in this slab could entrain additional snow and become larger. A series of melt/freeze cycles last week limit stability concerns to snow which has fallen in the past two days. Expect varied slab characteristics in this new snow which is loading on shifting and increasing wind with potential for touchy slabs in much of our terrain.

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 8:15 a.m., Sunday, February 18, 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

2018-2-18