Avalanche Advisory for Thursday, March 24, 2016

This advisory expires tonight at 12:00 midnight.

Tuckerman and Huntington Ravines have Moderate avalanche danger.  Natural avalanches are unlikely and human-triggered avalanches are possible.  Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully to identify features of concern.

AVALANCHE PROBLEM: Wind slab is going to be the #1 problem again today.  Only about one inch of snow fell during the morning hours yesterday, but snow began again during the predawn hours on a light W wind. Continued snow this morning will taper to showers in the afternoon on a building wind.  Expect the avalanche danger to build through the day with new loading to accelerate as wind velocities increase late in the day.  New wind slab will load on a variety of snowpack instabilities that already exist in both Ravines, but primarily in Tuckerman. Many E facing slopes were rated Moderate yesterday so today’s weather event will push some areas to the upper ceiling of the definition, edging towards Considerable.  The Lip area of Tuckerman is in the bullseye to have natural avalanche potential first.

WEATHER: Snow this morning will taper to snow showers and fog this afternoon as temperatures warm from the current 16F up to the mid 20’sF by nightfall. Expect precipitation, up to 3″ (7.5cm), to increase in density slightly. Calm to light west winds this morning will increase and shift to the southwest ultimately blowing in the 40-55 mph (64-88kph) range. Expect reduced visibility through the day as precipitation is replaced by summit fog this afternoon due to incoming moist airmass.

SNOWPACK: As Jeff stated in yesterday’s advisory from his field work on Tuesday, spatial variability is the dominate personality of the Ravines right now. There are old icy surfaces, wind sculpted snow, and numerous density slabs as soft as 1 finger hard. Some of these slabs failed on several weak layers over crusts.  Some thin slabs near the surface, up to 30cm (12″) deep, failed upon isolation.  Although this was not the norm, compression test scores to CT8 produced concern.  Moving deeper, to around 75cm, stability increased, but with extended column scores between ECTP14 and 20 indicating a potential for crack propagation.

Today’s snowfall, between 1-3″ (2.5-7.5cm), will load on an increasing W wind, shifting from the SW.  Snow will load primarily on E and NE facing aspects in both Ravines.  The Lip, Centerbowl, Chute, Left Gully and Hillman’s will be most affected in Tuckerman while in Huntington, I would have most concern in Central, Pinnacle, Odell and South Gullies.  Showers will continue after dark with an additional 1-2″ expected overnight while winds increase from 60mph (96kph) late this afternoon towards 85mph (136kph) after midnight.  For today’s recreation activities expect avalanche likelihood and peak instability to come late in the day towards darkness.  Sometime during the overnight we will likely get beyond the highest probability window, into an increasing stability trend briefly before rising quickly tomorrow as rain is expected at all elevations.

The bottom line is E and NE facing slopes will move through the Moderate rating definition through the day, many being responsive to human triggers.  I have fair confidence that later today, as winds increase, a number of these will edge closer to a Considerable rating definition.  However, in most cases this reality should hold off until after dark.

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 8:15a.m., Thursday, March 24, 2016. A new advisory will be issued tomorrow.

Christopher Joosen/Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2716