Avalanche Advisory for Friday 3-29-2013

This advisory expires at 12:00 midnight tonight.

All forecast areas of Tuckerman Ravine and Huntington Ravine have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully and identify features of concern. The only exceptions to this rating are the Little Headwall, which have Low avalanche danger. Natural and human triggered avalanches are unlikely in these areas except in isolated pockets.

Another day, another uncertain upslope snow event. That was the focus of our forecaster meeting this morning. Several times this month we’ve seen upslope events drop much more snow than expected, and other times not much materializes. Yesterday we had the latter, with only 0.5” of snow falling on the summit and a dusting around Hermit Lake. Today’s forecast is similar to yesterday’s, with a trace to 2” (0-5cm) in store with NW winds blowing 25-40mph (40-65kph). The range of snow makes for a challenging avalanche forecast and puts more of the burden on you to pay attention to what is actually taking place throughout the day. (Of course, this is no different than what you should always be doing.)

Let’s start with the scenario that would produce the greatest avalanche concerns. Let’s suppose we do get 2” of snow with summit winds blowing at the upper end of the rating, around 40mph with some higher gusts. There have been approximately 3” of snow which has fallen in the past couple days, so we’d be looking at a grand total of about 5” of snow available for loading into lee slopes. That’s a lot of snow to be loaded into slabs in the ravines. Expect these to be pretty soft and weak in the most protected locales, such as the Center Bowl or Central Gully. Most other areas would also develop fresh new slabs under this scenario, whether through direct loading or cross loading, and the problems would most likely be found in the middle to the top of the gullies or slide paths. If it plays out, this worst-case scenario would have some areas pushing the upper limits of the Moderate rating. As one who travels frequently in avalanche terrain, this is the scenario I’d be expecting, that way I’m not disappointed when I decide to turn back due to worsening conditions.

I’ll preface the following scenario with the fact that wind speeds have already exceeded the 40mph mark. In this alternative best-case scenario, suppose winds do become light, around 25mph, and we only receive another trace amount of new snow. This may produce smaller pockets of unstable snow, but would limit the widespread development of slabs. Prior to the upslope snow of the last couple days (i.e. before Wednesday), stability was generally good. Some areas, such as Hillman’s and Left, had very stable snow. Others had mostly very stable snow with smaller areas of concern; Right Gully and Lobster Claw are examples. The center portion of Tuckerman, from the Sluice through Chute, had fairly good stability, but if one were to trigger something here it could be sizeable. In the absence of significant new wind loading from yesterday and into today, we’re left with good underlying stability, but will have concerns for human triggered avalanches in the uppermost slabs. In this situation with little snow and light winds, some areas would have difficulty getting into the Moderate range.

Hopefully you can see the range of possibilities today. Don’t expect to see much of the ravines today, they’re thickly in the fog at this time and we may not have much of a break until tomorrow. Speaking of tomorrow, we’ll be posting a Weekend Update later this afternoon with our thoughts on what’s in store for the coming days. Look for it in The Pit section of our website.

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 at 8:30a.m., March 29, 2013. 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

2013-03-29 Printable