Avalanche Advisory for Tuesday, April 21, 2015

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has Considerable and Low avalanche danger. The Lip, Center Bowl, Chute, Left Gully, and Hillman’s Highway have Considerable avalanche danger. Natural avalanches are possible and human-triggered avalanches are likely. All other areas have Low avalanche danger. Natural and human-triggered avalanches are unlikely except for small avalanches in isolated terrain features. 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: Rain today will create conditions that can lead to wet slab avalanche releases. In the Lip and Center Bowl, the problem stems primarily from the potential for runoff to overwhelm the waterfall’s existing drainage channels. This has led to very large destructive avalanches in past events like it. Other locations posted at Considerable have received new snow in the past 24 hours, which may have been capped off with freezing rain. As we warm further and transition to rain, there is a potential for this new snow to slide as either a wet slab or a wet loose avalanche. As precipitation changes back to snow later today, the problems created by rain on surface slabs will subside, but percolating water coursing down through the snowpack and into the headwall may still keep alive the chance for a waterfall blowout.

WEATHER: Put simply, today will be a nasty day in the mountains. Seriously, if you are reading this before leaving from Pinkham, I encourage you to think about how much you enjoy being soaked to the bone with temperatures in the 30’s F. Unless this is just your cup of tea, you might want to find an alternative to hiking to the bowl today. We’ve had a lot of precipitation fall on the mountain in the last 24 hours. Precipitation began as snow across much of the higher terrain, leaving a little more than 3” of snow at the summit before changing over to freezing rain. I don’t yet have a rain total for Hermit Lake, but at home in Conway I received 1.85” of rainfall by 5am. The potential exists for another 0.25” to 0.5” of rain to fall on the mountain today, possibly heavy at times this morning. As is always the case in the mountains, weather can come faster and heavier than the broader synoptic scale forecasts may indicate. It looks like more snow at the upper elevations in the coming days, so pay attention if your plans involve a trip to the mountains this week.

SNOWPACK: Today’s Considerable rating might be on the conservative side for areas such as Hillman’s. 3” of dense snow may not be much, but I do suspect some loading took place while winds were strong from the SSE and temperatures were below freezing. Rain on this new snow layer may simply be absorbed, or it may produce smaller wet loose avalanches. In the worst case scenario, an upside down slab may have developed that could release. Over in the Lip and Center Bowl, the concerns are much more serious. The hazard potential there is virtually unpredictable. There are no reliable tests or other ways to detect whether or not the waterfall will blow out a deep slab. Traveling into the bowl, even just into the flats near the bottom, puts you in the line of fire from this type of avalanche.

OTHER HAZARDS: The typical springtime hazards have emerged and it will be challenging to protect yourself from them today. You should be aware of the potential for falling ice, crevasses, and undermined snow. These objective hazards exist and to a large extent are beyond your control. My advice for today is to avoid the potential hazard entirely.

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 6:35a.m., Tuesday, April 21, 2015. A new advisory will be issued tomorrow.

Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713