Avalanche Advisory for Friday, March 20, 2015

This advisory expires tonight at 12:00 Midnight.

All forecast areas of Tuckerman and Huntington Ravine have CONSIDERABLE avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. Careful snowpack evaluation, cautious route-finding and conservative decision making are essential. The only exception to this rating is the Lower Snowfields and the Little Headwall. The Lower Snowfields has Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. The Little Headwall has Low avalanche danger. Natural avalanches and human-triggered avalanches are unlikely. 

AVALANCHE PROBLEM:  The dry, light snow that fell Wednesday night and Thursday will be transported by increasing NW winds and build wind slabs over a weak layer of this low density snow. Expect these wind slabs to be largest in lee areas of this NW wind such as Sluice, Lip, and Center Bowl with the greatest potential for a natural avalanche in these areas. Adjacent areas are less prone to avalanche naturally but still certainly possible. In Huntington, many areas in the lee of the NW wind will harbor dangerous wind slabs until the wind reaches higher into the 90 mph (145 km/h) range late in the day. At that point snow in Huntington will begin to be scoured out but not before becoming dangerously sensitive to human-triggering.

WEATHER: The increase in wind speed and shift to the NW was delayed yesterday keeping today’s forecast similar. Winds are forecast to reach the 50-70 mph (80-115 km/h) before ramping up further to the 70-90 mph (115-145 km/h) range. Wind speeds are currently already blowing out of the NW at 59 mph (95 km/h) which is the highest velocity since yesterday’s new snow accumulation. Increasing NW wind plus around 7” of snow on the summit yesterday are the bright “red flags” signaling our avalanche danger. Expect summit fog and blowing snow to hamper visibility though cloud cover should begin to clear late in the day as high pressure takes over. Temperatures will be well below zero so anticipate arctic conditions with a temperature around -15F (-26C). Peak gusts on the summit are expected to hit 110 mph (175 km/h) before diminishing through the night.

SNOWPACK: As discussed yesterday, a small but intense storm system dumped widely variable amounts of snow on the area Wednesday night. While 14” fell at Hermit Lake, only 4.6” fell on the summit with some amount in between falling in our start zones and above in our fetch zone. Snow shower activity yesterday deposited another 2.5” to 3” on the summit. All this snow was very light density which makes the snow easily transported by the wind and also very weak. This weak and uncohesive snow was enjoyed by a few skiers yesterday who It is likely that the slow ramp up of wind yesterday allowed for the weak layer of new snow to adjust somewhat to the new load being piled on by the wind. This is the primary reason why I feel that a High rating is not warranted today. That said, you will find slabs growing to a sizable dimension today with the potential for natural and human-triggered avalanche activity more than likely peaking mid-day. Sluice unleashed a wind slab earlier in the week but Lip and Center Bowl did not so consider deeper wind slabs to contribute to an avalanche coming from these areas. In Huntington, the timing for potential avalanche activity also would correspond to the typical climbers travel plans with scouring not occurring until later in the afternoon. At that point, you could look forward to potential lower avalanche hazard while climbing in sub-zero temperatures and winds pushing towards the century mark. It seems like tomorrow might be a better option.

The Continuing Education series continues Saturday night at 6:30 p.m. at IME in North Conway where the presentation and discussion will be on the subject of Terrain Management so come on down and join me in getting my avalanche geek on.

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 7:20 a.m. February 20, 2015. A new advisory will be issued tomorrow.

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

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