Avalanche Advisory for Monday, April 27, 2015

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Moderate and Low avalanche danger. Lobster Claw, Right Gully, Sluice, Lip, Center Bowl, Chute, and Left Gully have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Hillman’s Highway, Lower Snowfields, and Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features. Huntington Ravine is under a General Advisory. You will need to do your own snow stability assessments when traveling in avalanche terrain in Huntington.

AVALANCHE PROBLEM: Avalanche danger will be increasing today as wind slabs form during daylight hours. The danger will increase most quickly on slopes such as Right Gully and Sluice. Prior to new snow, areas such as the Lip and Center Bowl hold the greatest hazard and will receive cross-loading of new wind slab today. Should temperatures in the ravine stay on the warm side and precipitation falls as rain, there is the chance for either wet loose avalanches or wet slabs. The location for both of these wet avalanche problems would be across all forecast areas in locations that have collected snow from the previous week.

WEATHER: Another round of light precipitation is expected to fall today. Liquid equivalents in the 0.10” (2.5mm) range will bring another 1-3” (2.5-7.5cm) of snowfall to the summit. We expect this to fall as snow at the elevation of Tuckerman and higher, but temperatures will be very close to the point where it may fall as rain. This precipitation will coincide with an increasing wind from the N and NE, rising to 50-65mph (80-105kph) with higher gusts.

April has been a very snowy month on the summit, though unfortunately not all of this snow has fallen on lower elevations. This is very normal at this time of year, and it means that the weather you are experiencing at Pinkham Notch or at Hermit Lake may not be representative of what’s taking place above treeline. Today will be another example of this, and it’s the higher elevation weather that will play a role in the avalanche conditions more than what’s down below.

SNOWPACK: Today’s concerns are driven by two sets of factors. First are the pre-existing conditions. Were it not for incoming snow and increasing wind, there would probably be more areas rated at Low danger. The recent snowfalls have had some time for some stabilization, and in some locations the snow did not completely blanket the terrain in new slab. Areas such as the Sluice, Lip, and Center Bowl did show smooth blankets of new slab, while Hillman’s, Right Gully, and Lobster Claw have many locations with exposed old surfaces. If you’re venturing out into the right or left side of the ravine, be wary of areas of deeper snow. This is an indicator that wind loading has taken place and the snowpack might be unstable.

The second set of factors is related to the new snow coming today. We’re expecting some loading to take place on aspects facing south through east. How quickly this develops will depend on how much snow we receive and the wind’s ability to transport it from upper elevations down into the avalanche start zones. You’ll need to monitor this carefully, especially later in the afternoon.

OTHER HAZARDS: Be aware of the potential of falling ice, crevasses, and undermined snow. The best you can do to mitigate the risk from these objective hazards is to avoid them, especially during times when they are more probable. Recent cold has kept these in check to some extent. Emerging crevasses in the ravine and holes in the Little Headwall may be hard to recognize today due to being hidden by new snow. The greatest hazard today is the threat of avalanches and debris running on to the floor of the 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 Mount Washington Volunteer Ski Patrol, or the AMC at the Pinkham Notch Visitor Center and Hermit Lake.
  • Posted 8:15 a.m., Monday, April 27, 2015. A new advisory will be issued tomorrow.

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