Avalanche Advisory for Sunday, 3-24-2013

This advisory expires at 12:00 midnight, March 24, 2013.

Tuckerman Ravine has  CONSIDERABLE avalanche danger today.  Natural avalanches are possible and human triggered avalanches are likely. All forecast areas in Tuckerman Ravine have Considerable avalanche danger. The Little Headwall has Low avalanche danger. Natural and human triggered avalanches are unlikely in that location.

Huntington Ravine has  CONSIDERABLE and MODERATE avalanche danger. Central, Pinnacle, Odell, and South gullies have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are  likely. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.

Old man winter lashed out furiously yesterday.  Northwesterly winds gusted over 100 mph (160 kph) frequently yesterday morning and then again around 6 pm with wind holding steady in the 70-90 mph (110-145 kph) range for the past 36 hours.  Forecasted upslope snow again surprised us with it’s intensity through the day so it was no surprise that the summit recorded about 6″  (15 cm) of new snow.  We recorded 20 cm (close to 8″) at our wind sheltered snowplot at the Harvard Cabin. Though both ravines that we forecast remain shrouded in fog, there is no doubt that the new snow and high winds resulted in natural avalanche activity yesterday and/or overnight. How widespread and which gullies ran will remain to be seen this afternoon when forecasted clearing will hopefully  allow us to get into the field for a closer look. Though diminished visibility for the past 36 hrs has reduced our ability to forecast with the high level of detail that we all like, several factors allow us to lower the danger ratings from yesterday while remaining conservative.

Windspeeds over 100 mph (160 kph) generally scour the gullies in Huntington Ravine but allow more loading and crossloading in gullies with a similar aspect in Tuckerman Ravine due to it’s lower, slightly more sheltered location from northwest winds. Our windslab problem usually reaches its zenith during the wind event when avalanches tend to occur due to the great weight of the new snow rapidly overwhelming the strength of a weak layer.  Though we have turned the corner today on the rapid loading due to diminishing winds, there is still the risk that today’s upslope snow, falling on moderate winds, could trigger a natural avalanche in Considerable rated areas. This fact coupled with an inch or two of snow falling on moderate winds in the loading speed range, lead us to believe that human triggered avalanches are pushing the upper end of the definition of moderate in areas so rated. Improving weather conditions today will increase the likelihood of a person traveling into a start zone and triggered an avalanche that could sweep the floor of Tuckerman Ravine, so I would consider the consequences carefully before entering this area.  The Huntington Ravine gullies will have piles of snow at the start of the gullies and on the approach to the steep bits of ice.  We have had plenty of examples of people triggering deep slabs in the lower reaches of  Central, Pinnacle and Odell gullies following similar weather conditions.

Refer to the photo gallery and you will see that many of our start zones and bed surfaces have increased in size and smoothed out quite a bit due to the 20″ of snow which fell on Tuesday and Wednesday (March 19-20) resulting in the possibility of much larger avalanches that will run further than they have all season.  Remember too that snowfall in the early stages of yesterdays wind event will form a softer layer lurking beneath the harder windslabs on top so frequent digging to find this layer would be critical to avoid being fooled by the firm snow on top for those choosing to tangle with avalanche terrain today.

Lots of soft snow exists on lower elevation treed trails and slopes like the Sherburne ski trail.  The Little Headwall has some holes in the streambed andsome ice to deal with but it is skiable. Though still bushy, the Lower Snowfields could provide some good skiing and riding but don’t ignore the significant threat that looms above in the Duchess and the lower reaches of Deadend Gully. Many folks ski on the treed slope below and between the mouth of Right Gully and Lobster Claw. The trick is to avoid the runouts of all the gullies and to bear in mind that the slope has a steep section of windloaded snow near the base of the cliff as well as some pockets in the middle which can avalanche so use solid travel skills in this terrain.

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 8:30 a.m. Sunday, March 24, 2013. A new advisory will be issued tomorrow.

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

2013-03-24 Print friendly