Avalanche Advisory for Tuesday, 2-28-2012

This advisory expires at 12:00 midnight, Tuesday, February 28 2012.

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. The Sluice, Lip, Center Bowl, and Chute have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Lobster Claw, Right Gully, Left Gully, Hillman’s Highway, and the Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. The Little Headwall has Low avalanche danger. Natural and human triggered avalanches are unlikely.

All forecast areas of Huntington Ravine have MODERATE avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. 

Today is a day of changing avalanche danger. Yesterday’s weather forecast for 1-3” didn’t quite pan out as we had hoped, with just 1” of silky 10% density snow falling at Hermit Lake. This is OK, though, because any snow is better than no snow this season. Late yesterday morning, winds began to transport snow around Tuckerman Ravine. This snow was leftover from the weekend storm and was made available for loading by a slight shift in wind direction. Fracture lines in the bowl were refilling even before any new snow began to fall. Later in the afternoon, when light snowfall started, the winds also began to accelerate. This trend has continued to the present time, with winds blowing even stronger than the morning forecast (currently gusting over 100mph/162kph) and light snow flurries still in the air. All this is adding up to the idea that there is sufficient loading taking place at this time that you should be thinking about naturally-triggered avalanches being possible in some locations. The Sluice definitely has my attention, since we believe it did not avalanche during the weekend cycle while slopes on either side of it did. Adding another layer of new slab on top might be just the load it needs to fracture and fail. As I mentioned in yesterday’s advisory, getting into an avalanche in the Sluice would carry severe consequences due to the terrain traps in the runout below. Additional loading on the bed surface in the Lip and Center Bowl could also produce naturally-triggered avalanches today.

The changing part of this forecast has to do with the high pressure system that is expected to take hold and clear the mountain of its foggy shroud. As this moves in, wind speeds will be decreasing, which is a two-sided coin in this situation. Current wind speeds are doing a good job of scouring new snow out of many forecast areas, but as speeds diminish, the rate of slab development will increase. This will continue either until there is no longer any snow available for winds to move, or until wind speed drops off significantly. The safe bet today is to expect further wind loading to be taking place until visibility improves and shows you that the loading is over. By the end of daylight hours, I think the Considerable rated areas will have dropped down into Moderate territory, but that still means there is the possibility of a person triggering an avalanche. I also think there might be some areas of Huntington and Tuckerman that won’t hold onto much new slab. If this is the case, late in the day the hazard in these areas would be dropping as well. Until visibility improves, you won’t be able to determine whether or not this has happened. Basically, if you’re staying on the hard old surfaces you’ll avoid instabilities altogether.

I had the not-so-fun experience yesterday of trying to ride a snowboard out through the Little Headwall. Attempting this in its current state will put you into bushwack to avoid the open streambed, followed by a couple turns on the Little Headwall to avoid the open water hole, then down into slightly more open bushes down below. You’re not missing much by taking the hiking trail down. Maybe some new snow on Wednesday night and Thursday will change things here, but I’ll believe it when I see it.

 

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 8:35am. A new advisory will be issued tomorrow.

 

Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2012-02-28 Print Friendly