Avalanche Advisory for Thursday, February 11, 2016

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine will have High and Considerable avalanche danger. The Sluice, Lip, Center Bowl, Chute and Left Gully will have High avalanche danger. Natural avalanches are likely and human triggered avalanches are very likely. Very dangerous avalanche conditions will exist and travel in avalanche terrain is not recommended. Right Gully and Hillman’s Highway will have Considerable avalanche danger. Dangerous avalanche conditions exist. Natural avalanches are possible and human-triggered avalanches are likely. Careful snowpack evaluation, cautious route finding and conservative decision making is essential. The Lobster Claw, Lower Snowfields, and Little Headwall remain not posted due to a lack of snow in these locations.

Huntington Ravine will have Considerable avalanche danger. Dangerous avalanche conditions will exist. Natural avalanches are possible and human-triggered avalanches are likely.

AVALANCHE PROBLEM: Today’s primary avalanche problem will be the rapid growth of Wind Slab.  The secondary problem will be Loose-Dry avalanches a.k.a. sluffing. Three days of light density snow and low winds has made a lot of snow available in the alpine zone for today’s big wind ramp up.  Expect touchy slabs to grow quickly during the second half of the day.  New wind slabs will grow on a loose, low density layer that should act as the dominate weak layer leading to natural avalanche issues during daylight hours this afternoon.  Expect the climb from dawn’s Moderate danger, through Considerable this morning, and in some Tuckerman locations reaching High later.  The timing will be directly related to the wind speed increase.  Very steep terrain, such as the Huntington gullies, should see Loose-Dry sluffing as well as Wind Slab issues.

WEATHER: About 8″ (20cm) of 4% low density snow has fallen on the summit of Mt. Washington in the last few days. During that period winds have been low to moderate for Mount Washington, which has transported little amounts of the available alpine snow into the deposition of the Ravines.  That will all change today as NW winds increase, gusting to 75mph (120kph) this afternoon. Additionally, new snowfall up to 2″ (5cm)will also mix in with wind transported snow.  Temperatures will fall to -10 to -15F (-23 to -26C) today as we begin a very cold several days. Expect a plummeting mercury in the heart of the weekend with potential summit lows hitting -30F (-34C) Saturday night. (Yes, before windchill)

SNOWPACK:  The knife-hardness, melt-freeze crust formed from the warm spell last week (Feb. 3 and 4) will be serving as the primary bed surface for today’s avalanche activity. 3.3” of snow fell soon after the formation of this crust, forming fairly small, somewhat stubborn wind slabs peppering our terrain. On top of these layers, 8” (20cm) of light density (4%) snow fell over the past three days. Unusually low wind speeds and cold temperatures have left this snow unchanged and in place throughout our terrain. The light density snow will serve not only as a sensitive layer for failure in our start zones, but also as the raw material in the alpine for winds to transport and form thick slabs in multiple start zones. These slabs will be soft enough to be sensitive to human-triggered and capable of producing avalanches large enough to bury and kill a person. If an analogy helps to clarify today’s situation, try this one…the floor of the Ravines is the muzzle of the cannon and the Alpine zone is the breech. This weapon is currently loaded, primed and aimed directly at the runout zones of Sluice through Left Gully, as well as several of the gullies in Huntington. The trigger will likely be squeezed sometime this afternoon, then reloaded with more ammo and fired again. These avalanches will not require a human trigger and will form and reform rapidly as winds increase. Travel into our terrain will require an early start and exit from avalanche terrain with an experienced and vigilant watch on weather and snowpack conditions.

The Lion Head Winter Route is open and the quickest route to the summit that avoids avalanche terrain. The John Sherburne Ski Trail has improved with recent snowfall but many obstacles, including water bars, lurk just beneath the surface.

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 7:55 a.m. February 11, 2016. A new advisory will be issued tomorrow.

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