Avalanche Advisory for Sunday, March 11, 2018

Huntington Ravine has Considerable and Moderate avalanche danger. Central, Pinnacle, Odell, South, and Escape Hatch Gullies have Considerable avalanche danger. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. North, Damnation, and Yale Gullies have Moderate avalanche danger. Evaluate snow and terrain carefully to identify features of concern.

 Tuckerman Ravine has High and Considerable avalanche danger. The Lip and Center Bowl have High avalanche danger. Very dangerous avalanche conditions exist. Travel in avalanche terrain is not recommended. Lobster Claw, Right Gully, Sluice, Chute, Left Gully, and Hillman’s Highway have Considerable avalanche danger. Careful snowpack evaluation, cautious route finding, and conservative decision making are essential. The Lower snowfields is rated Moderate and the Little Headwall is rated Low due to a less developed snowpack.

AVALANCHE PROBLEM: Wind Slab formed in the past 24 hours is our primary avalanche problem, with older wind slabs from our recent successive storms adding complexity to the upper snowpack. Significant snowfall yesterday combined with westerly winds to transport significant snow into lee terrain and cross load other areas. The resulting wind slabs will vary in hardness and could be large. Expect them to be reactive to a trigger. Human triggered avalanches are very likely in High rated areas. Peak instability likely occurred last night, but we don’t expect these slabs have gained much strength since then. Two known close calls occurred yesterday, including a skier caught and carried in Gulf of Slides by an avalanche that occurred while the party ascended.  Shortly after, two skiers were knocked off of their feet at the base of Hillman’s Highway by a natural avalanche. The Hillman’s avalanche is a reminder that low angle areas in our terrain, especially the floor of Tuckerman Ravine, are in the runout of steeper terrain above and should be treated as avalanche terrain. Moving one at a time and carrying avalanche rescue gear is important.

 WEATHER: Yesterday brought continuous and often heavy snowfall, totaling over 9” at both the summit and Hermit Lake. Wind blew out of the W with a few brief shifts NW, increasing through the day with peak summit gusts over 80 mph in the evening. Both wind and snowfall tapered overnight to the current light snow showers and W summit wind of 50 mph. Another 1-3” of snow is forecast today as wind decreases by this evening to under 30 mph out of the NW. We may see another trace to 1” of snow tonight and likely no snowfall tomorrow as wind remains below 30 mph.

SNOWPACK: Winter is back in a big way. The snowfall wouldn’t let up yesterday as westerly winds ideal for transporting snow out of our primary fetch zones increased through late evening. The old icy crust that snow struggled to stick to last week is certainly still a player in our snowpack, and we expect that new snow is finally building unstable slabs on this crust rather than being scoured away by wind. The extent of slab development versus scouring to this crust is our key uncertainty today, with no visibility to middle and upper avalanche start zones since Friday. The wind slabs formed in the last 24 hours could be quite large and well connected, but there is also a chance that some old surface is exposed. Overall we expect that these recently formed slabs are poorly bonded to the old ice crust. Further, these recent wind slabs are likely not bonded well to snow deposited earlier in the week in many areas. Without visibility into the upper terrain it’s wise to travel as if our upper start zones hold large slabs capable of avalanching naturally and running a long ways.

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 Harvard Cabin.
• Posted 8:20 a.m., Sunday, March 11, 2018. A new advisory will be issued tomorrow.

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