Apr 272015
 

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

2015-04-27

 Posted by at 8:16 am
Apr 262015
 

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. The only exceptions are the Lower Snowfields and Little Headwall which have Low avalanche danger. 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: Wind slabs exist throughout much of the ravine, providing snow stability conditions from the upper end of the Moderate range right down through the lower end of the range. Your terrain choices will certainly play a role in how much exposure you have to the avalanche hazard. Remember, by the time you have reached the floor of Tuckerman, you have already entered avalanche terrain and are at risk of an avalanche hitting you and your group from above. The areas of greatest concern are in the Sluice, Lip, Center Bowl, and Chute, as well as in the flat terrain beneath these areas.

WEATHER: Today will be much like yesterday as far as weather is concerned. We currently have some visibility, but with the forecast as it is, I think the prudent thing would be to expect thick fog to obscure sight lines at elevations above Hermit Lake. If visibility gets better, we should consider ourselves fortunate. There is a chance for a light snowfall to bring a trace to 2” to the summits, though I doubt if we get this it will affect snow stability to a great degree. Temperatures in the ravine will rise to somewhere near the freezing mark, but the fog and humidity makes things feel much less comfortable than a typical 30-35F day.

SNOWPACK: The story of the snowpack begins with a buried melt-freeze crust layer that is still holding heat and moistening the snow immediately above it. However, you don’t have to look far above the crust to find cold dry snow with a layer of weak rimed crystals mixed in. Slab that built from the recent snow on top of this weak layer is denser and dry. If you are on foot, you’ll feel the discomforting “upside-down” snowpack, which should raise the hairs on the back of your neck. If you’re on skis, you might not notice this underfoot, but a couple pole-probes should alert you to the presence of weak snow under strong snow. The majority of the new wind-loaded slab has built in the mid-elevations of the ravine, such as directly above and below the ice in the Center Bowl. Hillman’s has old surface showing in places all the way to the top, but the narrow section just above the fork appears to be holding deeper slab. Where we poked around under Right and Lobster Claw, the slabs were between knee-deep and thigh deep, but there are pockets of old surface showing here and there as well. This leads us to believe that there is a wide variety of stability falling within the Moderate range throughout all areas.

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.

The Sherburne Ski Trail is open about 2/3 of the way down. You’ll see the rope across the trail directing you back to the Tuckerman Ravine Trail, where you will need to hike 3/4 mile down to the parking lot.

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 8:30 a.m., Saturday, April 26, 2015. A new advisory will be issued tomorrow.

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

2015-04-26

 Posted by at 8:30 am