Apr 252015
 

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger today. Natural avalanches are possible and human-triggered avalanches are likely in The Sluice, Lip, Center Bowl, and the Chute and are rated CONSIDERABLE as a result. All other areas have Moderate avalanche danger. Natural avalanches are unlikely but human-triggered avalanches are possible in Lobster Claw, Right Gully, Left Gully, Hillman’s Highway, and Lower Snowfields. The only exception is the Little Headwall which has Low avalanche danger but has some open holes in the waterfall area. Use care if riding this and start from Connection Cache down the trail from the floor of the Ravine. 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: A surprising amount of recent new snow and ideal wind speeds for loading lee slopes have built Wind Slabs in Tuckerman Ravine. These wind slabs are likely to generate medium to large size avalanches, sensitive enough to be triggered by a skier, rider or climber and will have the ability to propagate a crack a long distance. They will be more than capable of burying a person and killing them by suffocation or trauma. This is true in Moderate as well as Considerable rated areas. Lower angle areas with bushes and rocks may be less prone to avalanche but could still be swept by debris from avalanches starting higher in the terrain. Once you pass the first aid cache on the way into the Ravine, 15 minutes up from Hermit Lake, you are in avalanche terrain.

WEATHER: Low visibility is expected to be a problem all day. Flat light and fog will make identification of critical snowpack details, as well as spotting people in avalanche start zones above you, a significant challenge today. A trace to 2” (TR to 5 cm) of new snow will further complicate things and add to our stability concerns. Cloud cover will keep temperatures below freezing even as the ambient temperature rises to the low 20’s F on the summit. Expect a windy, cold winter-like day.

SNOWPACK: A grainy and textured bed surface of refrozen corn snow allowed the initial new snow falling on it a few days ago to bond. The snow just above is our weak layer due to it being deposited during very low winds. Think of this layer as generally intact snowflakes with weak arms trying to hold the overlying firmer wind slab in place. These flakes are currently quivering and shaking due to the strain of holding up the wind slab which is likely to be thick in many of our start zones. In total, 9” (23 cm) of new snow built this wind slab on 40-60 mph (65- 95 km/h) W and NW winds. The wind slab is soft enough to crack easily and depending on the location will be finger to pencil hard. We have not been able to verify what has naturally avalanched, what has potentially been reloaded and what is harboring the thickest wind slabs. Because of this we need to assume all locations still possess substantial hazard and instabilities. Looking ahead, keep in mind the weakening affect that heat and filtered sunshine will have on this slab.

OTHER HAZARDS: The typical springtime hazards have become less of a problem with the recent freeze-up. You should 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. Hazards such as emerging crevasses and holes in the Little Headwall may be hard to recognize today and tomorrow, 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 will have the lower section closed. You can ski (mostly) to the #3 crossover, then pack up the skis for the 3/4 miles of hiking down the Tuckerman Ravine Trail.

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 25, 2015. A new advisory will be issued tomorrow.

Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713

2015-04-25 Print friendly

Apr 242015
 

Talk about full on winter!  It’s really hard to believe it’s almost May with the full on conditions today.  No visibility, temperatures in the teens, and 8.3” of snow in the past 48hours as made for more like a February afternoon than a typical spring day.  We are most concerned about the increasing avalanche danger that has developed over the past 24 hours with some areas currently bumping the upper end of the Considerable rating.

Fine grains are mixing in with average sized crystals which are producing a high water content per inch of snowfall packing into some fairly dense slabs.  As we expected the main weaknesses can be found above the old surface in lower density slabs created yesterday during periods of light wind.  Snow should taper overnight, but forecasts expect continued low visibility and temperatures in the high teens, perhaps reaching 20F on the summits. A blustery morning should give way to a diminishing wind in the afternoon, but currently it appears a chance of precipitation will keep all of us on our toes for the day.

With the information I’m seeing right now, along the weather that was slapping my face today, there is no way to sugarcoat or get around the reality that we will have avalanche issues tomorrow.  Expect to see an elevated avalanche danger rating for a number of areas with some “Considerable” slats probable.  Avalanche experience, skills, equipment and a history of good conservative decision making will be important.  If you have these skills and abilities several other issues and challenges would run through my mind.  1. With potential low visibility, and being a Saturday in April, I would have a fair amount of angst for triggers above me that I can’t see.  Expect some users coming in from multiple locations like hyenas converging on desired prey   2. Will someone adjacent to you, seemingly far away, trigger an avalanche that will propagate to your location.  Or 3. To ski something safely will ‘ski cutting’ a slope to clear it send snow down onto others below.  Frankly, slab instability and lots of people just don’t mix in the confines of an alpine cirque with avalanche paths that converge in multiple locations.  It is very difficult to mitigate the multiple hazards that are reasonable during a quiet day midweek versus dealing with a busy Saturday.  It can spell a disaster mixing hazards and crowds.  I don’t say these things lightly, but I think it’s important to accurately portray the potential situation tomorrow.  And although it’s not lining up as the cover shot of the “Worst Case Scenario” books it might be found on page 5 or 6.

Okay that was important to get across. Now how could it be not all that bad?  Loading and snowfall today has me believing that we are fully in the midst of Considerable avalanche danger.  This means that natural avalanches are possible.  If this occurs in numerous slide paths today/tonight we may rid ourselves of a good deal of hazard.  Although this is hard to plan or count on, it’s a possibility.  If snow shuts down overnight the concern for natural avalanches will dissipate a bit tomorrow which may leave us with a number of areas potentially being Moderate on Saturday.  This is quite plausible, but we will undoubtedly have concern for human triggered avalanches.  “Moderate” means a lot of different things to people.  Read the full meanings, size, and potential destructive forces for “Low”, “Moderate”, and “Considerable” in the scale below.  For a minute, focus only on the definitions for LOW and CONSIDERABLE.  There’s a pretty big gap between them isn’t there!!??  Well that’s the hole MODERATE is trying to fill.  So in reality there is a difference between instability that is just a bit above Low versus just below Considerable.  I think tomorrow’s Moderate will be just coming off of Considerable.

danger-scale-english

I recognize these are hard things to plan around for coming to the mountain or not, but for what I’m seeing it may not be the best Saturday to head for east facing higher terrain from the Gulf of Slides to the Northern Presidentials.  Some improvement for Sunday is likely, but anticipate some lingering avalanche instabilities.  Truthful and accurate reporting is important to us and I frequently ask myself the self-monitoring question “Am I crying wolf?”.  Although I do believe things can play out a number of ways overnight the above discussion reflects a high likelihood of how it will all play out tomorrow.  Be sure to check the Avalanche Advisory each morning before heading up into avalanche terrain.  See Jeff’s video post about descending from the Ravine.  We’ll see you in the hills or on the internet. Chris

 Posted by at 6:30 pm