Avalanche Advisory for Friday, April 24, 2015

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Considerable and Moderate avalanche danger. The Sluice, Lip, Center Bowl, Chute, Left Gully, and Hillman’s Highway have Considerable avalanche danger.  Natural avalanches are possible and human triggered avalanches are likely. The Lobsterclaw, Right Gully, and the Lower Snowfields have Moderate avalanche danger. Natural avalanches are unlikely and human-triggered avalanches are possible. (The Little Headwall is falling apart and is not recommended. See posted video on our website if reading this hardcopy). Huntington Ravine is under a General Advisory. You will need to do your own snow stability assessments when traveling in avalanche terrain in Huntington. A danger of falling ice exists, and will persist until it all comes down.

AVALANCHE PROBLEM:  As of midnight the summit received 6.7″ (17cm) of snow during the previous 36 hours.  Since then it has been snowing lightly each hour which will continue through the day with up to another 2″ (5cm) forecasted. Therefore, expect Wind Slabs to exist and more to develop into the afternoon.  Anticipate the most instability on lee slopes of W and NW winds rated at “Considerable” such as the Sluice, Lip, Center Bowl/Headwall and Chute. Also be ready for areas posted at “Moderate” to be on the upper end of the rating’s definition, hedging towards Considerable this afternoon. With an increasing wind anticipate new layers near the surface to be denser than the layers deposited yesterday creating a classic, unstable and “upside down” wind slab.

WEATHER: The unsettled period of weather over the past couple of days, which will linger into the weekend, has been delivering a consistent slow steady snowfall.  6.7″ (17cm) of snow recorded in the past 36 hours, coupled with 2-5″ (5-13cm) expected over the next day, will continue our avalanche danger concerns into the weekend. Wind speeds over the past several hours have increased into the mid 60’s mph (95+kph) from the NW. This trend will dominate the day with velocities crawling towards 70+mph (112+kph)this afternoon. Summit temperatures are beginning the day at 12F (-11C) and will not move up much making for a cold winter experience.  Be ready for all these factors to work together limiting visibility in the alpine zone.

SNOWPACK: On Thursday snowfall began on a S wind and shifte d from the W during the last 4″ (10cm) of accumulation. W winds were moderate, blowing in the upper 30’s mph (50kph) for the vast majority of daylight hours.  Since midnight, speeds increased and have been gusting over 60mph (95kph) this morning. This general theme will create an unstable snowpack situation by building dense slabs with smaller wind beaten particles over lighter layers that developed yesterday.  These lighter less dense slabs should be the weak layer to look for in your stability tests.  I think you will find this above the interface with the old hard surface as initial bonding was fairly good.  Today requires avalanche experience, training, and a history of good decision making in unstable snow.  We are not in spring and have new cold snow instabilities to deal with that currently exist and will continue to build into tonight.   The avalanche hazard has increased from yesterday, although still within the Considerable rating, due to additional snow and higher wind speeds.  We are not yet at peak for these instability issues so expect an increasing hazard as the day wears on.  We’ll discuss the prognosis for Saturday and Sunday in the Weekend Update that will come out this afternoon.

OTHER HAZARDS: The typical springtime hazards have emerged. You should be aware of the potential of falling ice, crevasses, and undermined snow. The best you can do to mitigate the risk from these objective hazards is to avoid them, especially during times when they are more probable.  The move back into winter over the past 48 hours has limited the development of these problems.  However, expect emerging crevasses and some undermining hard to recognize, due to being hidden by new snow.  The avalanche dangers listed above lead today’s objective hazards with crevassess and undermining following behind.

The Little Headwall has suffered from a collapsed section. We are no longer recommending this as a route out of the Bowl. The Sherburne Ski Trail is closed from the lower switchbacks to the parking lot due to mud.  Please cross over to the Tuck trail at the arrow sign and walk the short distance to your car.

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 Mount Washington Volunteer Ski Patrol, or the AMC at the Pinkham Notch Visitor Center and Hermit Lake.
  • Posted 7:50a.m., Friday, April 24, 2015. A new advisory will be issued tomorrow.

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

2015-04-24