Avalanche Advisory for Saturday, February 21, 2015

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Considerable, Moderate, and Low avalanche danger. The Sluice, Lip, and Center Bowl have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Lobster Claw, Right Gully, the Chute, and Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Left Gully, Hillman’s Highway, and the Little Headwall have Low avalanche danger. Natural and human-triggered avalanches are unlikely except in isolated terrain features.

All forecast areas of Huntington Ravine currently have Low avalanche danger. Natural and human-triggered avalanches are unlikely. Watch for unstable snow in isolated terrain features.

AVALANCHE PROBLEM: The existing wind slab is the primary problem for today, followed by the growth of new wind slab as snow begins to fall this afternoon and evening. Numerous naturally-triggered avalanches occurred recently on a variety of slopes, which should be an indicator of potential instability today. The area of greatest concern is in the Sluice through Center Bowl of Tuckerman, though all forecast areas of Tuckerman should be treated with caution today. Even those rated Low may hold smaller isolated pockets of unstable snow, the Little Headwall is one example of this. New snow this afternoon and evening will cause avalanche danger to rise, possibly exceeding some of today’s ratings before midnight.

WEATHER: Today is a good day to get out early and move quickly. Weather will be deteriorating as clouds lower, snow falls, and winds increase in velocity. Current winds of 40mph (65kph) gusting to 50mph (80kph) are already enough to cause low drifting snow to cascade down the headwall of Tucks. Much of today’s avalanche danger is brought on by ~18” (46cm) of light density snow (as measured at Hermit Lake) that fell this week, followed by winds yesterday afternoon and evening gusting in the 80-90mph (130-145kph) range.

SNOWPACK: We’ve had a good avalanche cycle in the last 24 hours, with large slides in many areas. I’m not sure which is my favorite avalanche this morning, the summer Lion Head Trail where it traverses at treeline or the one in the upper Chute. Both tell a good story about what’s happened with our snowpack just recently. Although winds have subsided a good deal since most of the loading took place, cold temperatures are going to keep a lot of the snap in the slabs that did not avalanche. The Lip and Center Bowl look like they may have already slid once, but if they did, reloading is hiding much of the evidence. The easy weak layer to look for is going to be weak, soft snow deposited before noontime yesterday. It will be much softer than the slab that is likely sitting on top of it. However, don’t only look for this structure. Very often, it’s subtle changes in wind speeds or directions that can create weak interfaces within a slab layer. These vary widely from one place to another, so be sure collect a lot of information today that’s relevant to your intended route.

Huntington Ravine starts today with a heavily scoured snow surface. I don’t expect avalanche danger to rise much during daylight hours, but after dark it may go above the Low threshold.  Within the Low rating, there may be small terrain features with unstable pockets of wind slab. Below the ice bulge in Central is one such example.

Looking for something to do tonight? Come by International Mountain Equipment at 6:30 for a free avalanche continuing education session. Snow Ranger Frank Carus will be presenting tips and techniques for effective terrain management in Tuckerman and Huntington 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 the Harvard Cabin.
  • Posted 8:30 a.m. February 21, 2015. A new advisory will be issued tomorrow.

Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2713