Avalanche Advisory for Thursday, March 27, 2014

This advisory expires at 12:00 midnight.

Tuckerman Ravine as Moderate and Low avalanche danger. Lobster Claw, Right Gully, Sluice, Center Bowl, Chute and Lower Snowfields have Moderate avalanche danger. Natural avalanches unlikely and human triggered avalanches are possible.Evaluate snow and terrain carefully. Left Gully, Hillman’s Highway and the Little Headwall have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

Huntington Ravine has Moderate and Low avalanche danger. Yale, Central, Odell, South and Escape Hatch have Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully. North, Damnation and Pinnacle Gully have Low avalanche danger. Natural and human triggered avalanches are unlikely. Watch for unstable snow on isolated terrain features.

AVALANCHE PROBLEM: The main avalanche problem today is stiff Wind Slab. Though probably difficult to trigger in most areas, these firm Wind Slabs could propagate a crack and reach a dangerous size in select areas. These slabs are becoming Persistent Slabs as continued cold weather slows the bonding process. Reduce your exposure to these slabs with careful route finding in either Ravine.

WEATHER: High winds yesterday afternoon and overnight have moved and packed snow into slabs and scoured other areas. Northern gullies in Huntington appear to have been pretty well blasted by the wind, although some of the more wind resistant harder slabs certainly may still exist. Drifted snow, bark and branches litter the Tuckerman Ravine trail, clear signs of the harsh wind yesterday which peaked at 104 mph (46.4 m/s or 167 kph) with steadier winds near 90 mph (145 kph) for several hours. Northwest wind blowing near 80 mph (130 kph) will diminish to around 70 mph (113 kph). The wind combined with an air temperature crawling up into the teens will keep conditions noticeably colder than an average spring day.

SNOWPACK: While wind speeds were obviously less in our Ravines than on the summit, you can rest assured that very little soft snow remains. Sluice and Center Bowl escaped the strongest wind, due to their lee location, and are nudging into a more serious, higher Moderate due to the size of the potential slab and steepness. I would place Central Gully in a similar category though it is probably more scoured. The high wind seems to have built these wind slabs lower in our terrain so stay “heads up” to the right of the Fan beneath Damnation and Yale as well as in the lower portions of Sluice through Left Gully. The wind slabs that you may encounter today are certainly firm underfoot but the existence of rimed particle (graupel) layers and clean shear interfaces can leverage the brittle property of this hard slab against you. It is somewhere between difficult to impossible to know exactly where a thin spot lies beneath the upper snow layers, even with an intimate knowledge of the terrain, so your best bet for travel today, if you are going to brave the cold and wind, is to avoid traveling on or below larger areas of these slabs. Remember that although these slabs may have the ability to bridge across terrain features, they are often unsupported from below as they grow thinner downslope, so the slab can be essentially hanging on the slope. Perforating the slab with boots, impacting the slab with the weight of several people or a starfishing skier or just stepping on a thin spot in the right place could leading to failure. Even Low rated areas may contain areas with this sort of concern so ignore the calendar and bring your avalanche safety mind and PPE. 

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. 3-27-2014. 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

2014-03-27 Print friendly