Jan 232015
 

This advisory expires tonight at 12:00 midnight.

Tuckerman and Huntington Ravines have Low avalanche danger.   Natural and human-triggered avalanches are unlikely, but watch for unstable snow in isolated terrain features. It is important to realize these pockets do exist and can produce smaller avalanches in remote steep locations.  This is a greater concern in Tuckerman than in the wind scoured gullies of Huntington.

AVALANCHE PROBLEM: Persistent Slabs are the primary avalanche concern today. These slabs exist as both as hangfire from the natural avalanche cycles on Sunday and as pencil hard slabs from the wind loading on Tuesday. These are most likely to be found beneath the highly wind protected upper ice flows in the Tuckerman Headwall area. The second threat is from softer wind slab that developed as winds died down on Tuesday. Look for these smaller, but touchier slabs (1F hardness) behind terrain features in strong lee areas such as lookers left at the top of Right Gully, and along steep buttresses.

WEATHER: Weather will start transitioning late today from the clear high pressure system to increasing clouds with the approaching low pressure from the south. However, nice weather will continue for a day in the mountains and should not affect snow stability. An increasing wind may move just a little alpine snow, but not enough to load in as a new problem. Late tomorrow and into the early Sunday morning we will pick up some new snow, albeit scant.

SNOWPACK: Field time yesterday and a lot of discussion led us to settle on a Low rating today despite the fact that Persistent Slabs more often than not for us earn a Moderate rating. The main driver behind the Low rating is that the persistent weak layer of facets in question was discontinuous in nature even before this last avalanche cycle. Persistent slabs are typically hard, stubborn and therefore resistant to a human acting as a trigger.  Although this is true for our current situation we also have limited weak layers keeping us from moving our concern to a higher rating.  In addition, we believe the tensile slab strength of varying depth is bridging over an occasional deeper facet layer or isolated graupel pool.  Intense spatial variability and the discontinuous nature of the slabs and weak layers lead us to believe isolated pockets of concern most accurately describe our snowpack. While you may find some smooth Q2 shovel shears among the wind slab layers you will generally find them “hard” and stubborn. There is a lot of bridging power in hard slabs like these. That said, I would be careful of any of these slabs sitting on top of ice flows such as in the Center Bowl area. As always, mitigate your exposure to avalanche threats by careful route selection.

Look for more terrain/conditions photos today on our Facebook page and possibly the new Flickr account if all goes well on the technology front. The Sherburne is not particularly enjoyable skiing unless you like hard snow and water bars. It is currently plagued with a brutal frozen rain crust on it’s upper half. Right Gully saw a half dozen skiers yesterday on firm but smooth and carvable snow. Many other areas such as Left Gully were much more bumpy due to wind whipped sastrugi. Chris is writing what may be his last weekend update today….look for that later today.

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 8:40 a.m. January 23, 2015. A new advisory will be issued tomorrow.

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

2015-01-23 print friendly

Jan 222015
 

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Moderate and Low avalanche danger. Right Gully, the Sluice, Lip, Center Bowl, Chute, Left Gully, and Hillman’s Highway have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanche are possible. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully to identify features of concern. The Lobster Claw, Lower Snowfields and the Little Headwall have Low avalanche danger. In these areas, natural and human-triggered avalanches are unlikely, but watch for unstable snow in isolated terrain features.

Huntington Ravine has Moderate and Low avalanche danger. Central and Pinnacle Gullies have Moderate danger. Natural avalanches are unlikely and human-triggered avalanches are possible. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully to identify features of concern. All other forecast areas have Low avalanche danger. Natural and human-triggered avalanches are unlikely; however, watch for unstable snow in isolated terrain features.

AVALANCHE PROBLEM: Wind Slabs that developed on Tuesday coupled with the hang fire from the avalanche cycle on Sunday night are the primary concerns today. Of particular concern would be the upper start zone of Right Gully, Sluice and the Lip. Most of the wind slabs are likely to be stubborn and resistant to triggering. A close second to these wind slabs are sluff piles beneath steep features which did not avalanche or were reloaded on Tuesday such as in Center Bowl and Chute. Huntington was more scoured by these winds, which were near 100 mph (160 km/h), on Tuesday. That said, Central and Pinnacle should be assessed for remaining wind slabs.

WEATHER: Highs in the teens F today coupled with light winds out of the west will do little to affect snow stability in either direction today. Winds are expected to shift from the W to NW and ramp up a bit from it’s current calm 5 mph (8 km/h) to around 30 mph (50 km/h) with higher gusts through the afternoon and evening.

SNOWPACK:  As Chris discussed yesterday, a wide range of snowpack issues exist in the Ravines. Not much has happened since then to either increase or decrease stability. A wet snow and freezing rain storm on Sunday was responsible for a widespread avalanche event on slopes and gullies with a more northerly facing aspect. The good news is that in many areas the cycle swept out the older persistent grain types associated with the January 4 crust.  However, Sundays snow/freezing rain line was right around the bottom of the Ravines and is already producing another layer of facets. A frozen crust also capable of producing these facets may have developed in some slightly higher elevations in the Ravines as well but its extent remains to be fully understood. Travellers should remember that firm or hard wind slabs that exist in many areas now can still be triggered if the right sweet spot is found. Often that spot is a thinner part of the slab. Multiple quick hand pits and continual assessment of your position relative to the hazard are more helpful in cases like these than one deep pit.

Sections of the Sherburne trail are very icy due to the freezing rain on Sunday.

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 8:10 a.m. January 22, 2015. 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

2015-01-22 print friendly