Mar 052015
 

This advisory expires at midnight.

Tuckerman Ravine has Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features.

Huntington Ravine has Moderate and Low avalanche danger. Central, Pinnacle and Odell have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features.  All other forecast areas have Low avalanche danger where natural and human triggered avalanches are unlikely except in isolated terrain features.

AVALANCHE PROBLEM: Wind Slab is the primary concern today followed by Persistent Slabs as a secondary problem. Over the past two days 4” (10cm) of new snow loaded in on moderate to very high winds creating new wind slabs in both Ravines. Wind Slabs can primarily be found in the center and some south side locations based on SW and W loading winds.  These are sitting on Persistent slabs that were beginning to be our primary problem near the end of last week.  In our Tuckerman field work, we were finding some weak layers that were going to early facets, but this was sporadic and not consistent. In areas where it is located, expect the persistent weak layer beneath these layers to yield   unstable test results.

WEATHER: 4” of snow, clouds and wind over the past 2 days has kept visibility poor with a thin veil muting the definition in both Ravines.  The forecast is expecting a clearing trend later today as a front brings in yet another round of arctic air.  Temperatures will fall to -10F (-23C) today and -20F (-29C) tonight.  Conditions will warm a bit, but we expect all negative numbers into the weekend.  Very high winds this morning should abate down to about 40-50mph (64-80kph) later today and through the overnight. Very cold air and wind do not create conditions for an increased stability trend, so expect avalanche problems to linger.

SNOWPACK:  The potential for natural avalanches has clearly subsided from areas being “possible” yesterday, to “unlikely” today.  Human triggered avalanches in the new wind slab are our primary concern today.  Based on some periods of very high winds you will likely find a mix of stubborn, stiff pencil (P) hard slabs in exposed locales and softer, one finger (1F) new snow in very protected terrain under some cliff bands, ice features, and buttresses.  There is a little uncertainty in our forecast this morning exactly where these different problems occur based on limited visibility.  Clearing is anticipated later today which will help you make navigation and terrain management decisions, but until then clouds will make this challenging.  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.

In Huntington, the northern side of the Ravine has limited stability issues and less to mitigate compared to snowfields near the rim of the southern side. The exits up high in the Escape Hatch and South have pockets to manage under a Low rating. In the Moderate rated Central, Pinnacle and Odell you will find issues lower down such at the base of Odell’s first ice pitch.  Generally, in Tuckerman you will find more stability on the north and south sides compared to more problems in the Sluice, Lip, Center Bowl and the Chute. Although all of Tuckerman is rated Moderate these 4 areas harbor the greatest potential for a larger avalanche based on the size of the slopes, the potential for surface wind slab avalanches stepping down into deeper persistent slabs and their start zone steepness.  Our persistent slab concerns are found mostly in these 4 areas and are of a limited to minor issue in other Tuckerman locations, and not much of an issue at all in Huntington.

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 8:25 a.m. Thursday, March 05, 2015. A new advisory will be issued tomorrow.

Christopher Joosen, Snow Ranger USDA Forest Service

2015-03-05

 Posted by at 8:47 am
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