Avalanche Advisory for Thursday 3-28-2013

Expires at Midnight 3-28-2013

Tuckerman and Huntington Ravines have MODERATE avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible.  Heightened avalanche conditions in specific terrain features exist.  Evaluate snow and terrain carefully to identify features of concern.

The dreaded “trace to 2″” has reared it’s head for both today and then once again for tomorrow.  These upslope snow events can be hard to deal with from a weather and avalanche forecast point of view.  If we get a trace obviously not much change will occur to avalanche danger, but if we exceed expectations a bit and if the winds are right, well then we can have some real problems.  These scenarios are a real challenge from the forecaster’s chair for us, and for you in the field.  Therefore it is critical that you pay attention to what is actually happening weather and avalanche wise as the day continues and use all your avalanche training and experience to make good choices.  Here’s my take on today’s situation.

Beginning yesterday afternoon light snow showers began and continued for 12 hours to about midnight delivering about 2.5″ (6cm) of snow on the summit.  This precipitation was brought in on a NW to NNW wind between 25 and 45mph (40-72 kph).  Early this morning winds shifted quickly and briefly came from the ENE before heading back through the NE at about 25mph (40kph).  They are expected to head back to the NW today and increase to about 40 mph (65kph). All the while, up to an additional 2″ (5cm) of snow is expected.  When adding Wednesday’s snow to today’s accumulation potential, with a moderate wind moving back and forth from the NW to the NE and back again, we have concerns for south facing slopes and gullies.   Specifically our concerns are focused on the Lobsterclaw, Right Gully, the Sluice, and the Lip in Tuckerman and North, Damnation, Yale, and Central gullies in Huntington.  These locales are in the direct lee of today’s anticipated wind.  I would also have an eye on crossloading in some areas facing E, however our historical experience with today’s anticipated wind speeds this should be quite limited.  The aforementioned gullies and slopes with a strong S facing component should pick up new wind slab in their upper start zones.  I would generally expect the main instabilities to be focuses near the rim where gullies top out. If we do receive closer to 2″ than a trace expect to be on the upper end, bumping the ceiling, of the “Moderate” rating definition hedging towards “Considerable”.  Begin thinking about natural avalanches moving from “unlikely” to being “possible”. Also, lookout for snow piling beneath ice bulges and forming slabs.

To recap the main points for the field today.  1.  Winds have moved from the NW to the NE and are now moving back to the NW from 25-45mph.   This will load new snow into mainly S facing aspects.  2.  Whether yesterday and today’s total snowfall is 2.5 or 4.5″ will make a big difference on whether we sit at Moderate or start leaning towards Considerable for S facing slopes.  Watch the weather and snowpack closely to make good choices.  3.  Look out for some isolated pockets of deeper slab below steep ice bulges and other midslope benches particularly in Huntington Ravine.  4. Much of our terrain will have good to very good stability if windspeeds do not increase and and new snowfall is light.

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 7:50am, March 28, 2013. A new advisory will be issued tomorrow.

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

2013-03-28 Print friendly