Avalanche Advisory for Wednesday, December 24, 2014

This advisory expires tonight at 12:00 midnight.

Tuckerman and Huntington Ravines will have HIGH avalanche danger today. Natural avalanches are likely and human triggered avalanches are very likely. Very dangerous avalanche conditions exist and travel in avalanche terrain is not recommended which includes runout paths.

AVALANCHE PROBLEM: Wet Slabs are the main avalanche problem today.  Several inches of new snow fell yesterday morning which has since transitioned to light rain, freezing rain and drizzle in the higher terrain.  Heavy rain today will rapidly increase instability pushing a number of slabs of varying density to their limit of strength causing some to fail. This will transition several problems to a singular wet slab issue. Expect natural wet slabs today.

WEATHER: The liquid gauntlet is about to begin.  A tropical system is setting it’s mass on the region expected to bring at least 1.5″ of rain to the mountains, much of it falling heavy at times.  Actual forecasted amounts (QPF) have been difficult due to the digital models having a history of trouble with this type of event.  Human forecasters are adding up to another inch to the potential amount and even more in isolated upsloping areas.  This makes the potential liquid window pretty large at 1.5″ to give or take 3″ over the next 24-30 hours.  Another question is wind speeds over the next 48 hours.  They will get ferocious, but forecasts differ on their level of violence.  Today we could see winds exceeding hurricane force on the higher summits gusting towards 90mph.  This upward moving trend will continue tonight, tomorrow and into Thursday evening when some meteorologists are discussing winds gusting to 140mph (224kph)!  Generally expect travel in alpine zones to be particularly horrific as temperatures drop tomorrow and the front moves in through the day.  Where the uncertainty stops is the question of precipitation type today.  The summit of Washington will be crawling towards its daily record with forecasted temperatures in the low 40’sF.  The mercury is anticipated to drift back below freezing after daylight tomorrow morning, changing precipitation back to snow.  Temperatures will continue to fall into the teensF after dark tomorrow night.

SNOWPACK: Typically the snowpack discussion is the longest, but it takes a backseat to the weather today.  This is because issues will become very clear over the next several hours leaving little room for doubt.  Heavy rain intensity rates on a variety of slab densities and thickness will move the Ravines from a current Considerable rating at 730am to the forecasted High avalanche danger.  Natural avalanches will be likely due to wet slab development.  Rain adds weight, melts bonds decreasing slab strength and can lubricate impermeable or semi-impermeable layers such as buried water ice or crusts.  Will every slope naturally avalanche? No.  However a variety of paths criss-cross and the potential for some stream blow outs from under snow water flows such as in Tuckerman’s Lip or Sluice, and Huntington’s narrow gullies, is possible. Therefore, a prudent call is to stay out of avalanche terrain.

Based on the rain and extreme wind forecast a multi day Holiday alpine terrain trip starting this morning would be a horrendous idea. Looks like we’re generally getting a Holiday stocking of coal today, but we’ll talk about a few presents of whiteness in the advisory tomorrow.

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 7:50 a.m. December 24, 2014. 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