Mar 042015
 

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Considerable and Moderate avalanche danger today. The Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Dangerous avalanche conditions require cautious route-finding and conservative decision making. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features.

All forecast areas of Huntington Ravine have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features

AVALANCHE PROBLEM: Wind slab is the primary concern today. The driving force behind the increase in ratings today is the new wind slab that developed overnight, and is likely to continue to build today. New hard slabs should be expected in all forecast areas. We anticipate the potential for reasonably large avalanches, with the areas rated Considerable holding the greatest potential for slab failure to step down into deeper layers and produce a larger avalanche.

WEATHER: This was not the storm of the year, but we are happy to have received another 3.5” (9cm) of snow yesterday on top of the 4″ that fell Sunday through Monday. The new snow came along with strong winds shifting from the SW to the NW with peak gusts from the W over 100mph around midnight. This is also around the time when snowfall shut down, but wind loading should be expected today with winds continuing from the W at 60-80mph possibly gusting over the century mark again later. There is a chance we will receive another trace to 2” (5cm) of new snow today, so pay attention to both windblown snow and newly falling snow.

SNOWPACK: The difference in ratings between Considerable areas and Moderate areas is due mostly to the composition of the snowpack prior to the onset of snow yesterday afternoon. Those areas rated at Considerable will have more potential weak layers and weak interfaces between layers.  These areas also have steep slopes in the direct lee of W winds that are more protected from the intense scouring of high winds. Prior to new snow, most of those rated Moderate had a stable snowpack due to heavy wind effects and scouring. There is a chance that some of these areas also were scoured last night during strong winds, but until you have the good evidence of this, your best bet is to assume that the slopes were loaded rather than scoured.

If you are out in the ravines today, you will likely have very poor visibility. You’ll need to pay close attention to the amount of snow falling and blowing around. As long as this is going on, you should be thinking about the potential for avalanches to be triggered naturally and running down into relatively flat terrain.  It will be very difficult to ascertain if you are in avalanche path runouts without good visuals unless you are extremely familiar with the terrain. As the definition for Considerable danger states, careful snowpack evaluation, cautious route finding, and conservative decision making are essential today.

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 8:20a.m. March 4, 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

2015-03-04

 Posted by at 8:32 am
Mar 032015
 

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Moderate and Low avalanche danger. Lobster Claw, Right Gully, the Sluice, Lip, Center Bowl, 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. Unstable snow may exist in isolated terrain features in these locations.

Huntington Ravine has Low avalanche danger. Natural and human triggered avalanches are unlikely.

AVALANCHE PROBLEM: The primary concerns today are wind slabs that developed during strong winds and upslope snow yesterday. There were some naturally triggered avalanches in Tuckerman, but slopes that avalanched were able to reload before the blowing snow began to diminish. The areas of greatest concern will be in the Sluice, Lip, Center Bowl, and Chute of Tuckerman. All of Huntington Ravine was heavily scoured and has very stable snow. Hillman’s and Left Gully are similarly Low danger, although more wind-hammered than scoured. The Lower Snowfields and Little Headwall have areas that may produce small human triggered slides.

WEATHER: Weather will be changing significantly through the day. We are starting with clear and relatively calm conditions. There is a little bit of low drifting snow blowing over the headwall which should cease as summit wind speeds drop down to 25-40mph (40-65kph). Clouds will build this afternoon and snow should begin falling after dark. Tonight’s weather is expected to increase the avalanche danger, but not until very close to the end of this advisory’s lifespan. Total snowfall from Sunday through today has been roughly 4”. It’s possible that more fell, but winds have made measurements difficult at our snowplots and at the summit.

SNOWPACK: Be on the lookout for areas where yesterday’s snow has been loaded into slabs. Don’t take the recent avalanche activity as an indicator of a stable slope. In fact you should be thinking just the opposite. In addition to hangfire, reloaded slabs on top of previous bed surfaces may not have had a good opportunity to bond well to the bed surface and could be just as reactive as the slab that had already avalanched. As mentioned, these are primarily in the Sluice, Lip, Center Bowl, and Chute. Also expect to find some new slab in Right Gully and Lobster Claw, but these routes may also offer more options for avoiding stability problems than the more exposed routes in the middle of Tuckerman.

Much of the new snow that fell yesterday has blown down out of the ravines and into the forests below. Judging from the amount of drifting on the Tuckerman Ravine Trail and Huntington Fire Road this morning, I suspect the Sherburne Trail is in fine shape with some fun drifting to play around on.

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 8:20a.m. March 3, 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

2015-03-03

 Posted by at 8:17 am