Avalanche Advisory for Thursday, January 29, 2015

This advisory expires at midnight.

Tuckerman Ravine has Moderate and Low avalanche danger.  The Lobster Claw, Right Gully, Sluice, Lip, Center Bowl, and the Chute have Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible.  Left gully, Hillman’s Highway, the Lower Snowfields, and the Little Headwall have Low avalanche danger.  Natural and human triggered avalanches are unlikely except in isolated terrain features.

Huntington Ravine has Moderate and Low avalanche danger.  North, Damnation, and Yale gullies have Moderate avalanche danger.  Natural avalanches are unlikely and human triggered avalanches are possible.  Central, Pinnacle, Odell, South, and Escape Hatch have Low avalanche danger.  Natural and human triggered avalanches are unlikely except in isolated terrain features.

AVALANCHE PROBLEM: Wind Slabs that developed from about a foot of snow from the recent storm are the #1 problem today.  Wind slabs formed initially on very high winds with an easterly component.  This created very hard slabs initially as the Ravines were on the windward side of early storm winds.  The second half of the Tuesday/Wednesday storm came in on a diminishing NE and N wind.  This loaded softer wind slabs on S facing aspects.  Expect wind slabs to be softer and easier to trigger on these S facing slopes and anticipate slabs facing directly E and N to be harder, more difficult to trigger, but resulting in larger avalanches if they fail.

WEATHER: Wind loading shut down yesterday afternoon as winds fell to 50 mph resulting in excellent visibility.  Today very low winds and sun will dominate the day until late when a shifting wind moves from the NW to the S and increase.   Late in the day gusts may move into the 60’s mph. (96kph).  This may cause some light new loading on N facing slopes.  New snow moving in tonight and all day tomorrow is expected to bring 4-8” of new snow causing an increase in avalanche danger for Friday and perhaps Saturday.

SNOWPACK: There are some slopes, facing towards the E, which lost snow due to wind gusts over 100mph (160kph) during the early parts of the storm. As winds subsided a bit and moved to the NE, NNE and then N, some of these slopes were cross-loaded and wind packed. Meanwhile, S facing slopes became heavily loaded with soft wind slab.  As some examples, you can expect soft slabs in the upper start zones of Huntington’s Damnation and Yale gullies as well as Tuckerman’s Lobster Claw, Right Gully and the Sluice.  These are considered as having Moderate danger and should be easier to trigger than the harder slabs facing E and N.  A number of these harder slopes such as the Center Bowl and the Chute also harbor Moderate danger, but will be more stubborn and difficult to trigger. However if they fail expect these harder slabs to propagate farther resulting in larger avalanches.  So areas posted as Moderate have some different issues within the same definition.  Both issues may result in dire consequences, but softer slabs will be a bit more straight forward to manage for avalanche skilled users than firmer wind hardened slopes.  I would be wary traveling out into the middle of a large hard slab so soon after this storm.  In areas posted at Low danger keep your eyes open for isolated snow instabilities such as the mid slope sections of Hillman’s and Left gully.

Late in the day a shifting, increasing, wind from the S may pick up some snow in alpine areas that have been protected by terrain features during the recent N wind.  Look for plumes late this afternoon as clues that some light loading on N facing slopes may be occurring.  Saying this, the probability this will cause new problems is remote, but worthy to note.  Expect snow tonight and all day tomorrow, adding up to 4-8” (10-20cm), to increase the avalanche danger into the beginning of the weekend.

We are now using the Winter Lion Head Route which is marked by orange signs half way up to Hermit Lake at the bottom and at treeline up top.  Expect a post holing slog until it is packed out, snowshoes could be helpful.   The Sherburne Ski Trail has improved dramatically.

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 8:45 a.m. January 29, 2015. A new advisory will be issued tomorrow.

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