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Issued
Fri, December 13th, 2013 - 7:00AM
Expires
Sat, December 14th, 2013 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is LOW this morning and will increase to MODERATE above treeline late in the day today.   Snowfall beginning midday, combined with winds will form slabs that will be very sensitive to human triggers.

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Fri, December 13th, 2013
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

For the majority of the day the main hazard will continue to be associated with early season conditions; breakable crust and rocks lurking just below a thin layer of new snow.  These are legitimate hazards and require extra time moving through terrain.

A small amount of new snow (~2” on Turnagain Pass and ~4” in Girdwood Valley) coupled with moderate winds out of the East, have created very shallow slabs in upper elevation starting zones.  Slabs are low volume this morning.

As the day progresses, new snow will begin to form slabs that will be very sensitive to human triggers.  The old snow surface consists of pockets of surface hoar sitting on a thin crust.  In areas sheltered from the wind new snow will sluff easily and should run long distances.  Again, these concerns will become more pronounced later in the day.  Should you find yourself out in the mountains as daylight wanes it will be worth avoiding higher elevation starting zones and steep terrain harboring newly formed slabs.

Weather
Fri, December 13th, 2013

The dry spell is over.   The mountains around Eastern Turnagain Arm have picked up between 1-4 € of new snow with .1-.2 € of water in the past 24 hours (slightly greater amounts in the Girdwood Valley).   Ridge top winds have shifted overnight and are now blowing out of the East at an average of 15 mph with gusts to 30 mph.   Temperatures have been in the single digits and are starting to creep up into the low teens.

A large low pressure system that is currently to our South is moving north into Prince William Sound.   As this system gains strength and moisture it will begin to scatter snow showers over the forecast area around midday.   Look for snowfall to pick up in intensity by late afternoon with the potential for an additional 8″ new snow by this evening.   Winds will be out of the East at 15-20 mph and temperatures at 1,000′ will warm up into the twenties F.

This system will bring continued snow as well as fluctuating temperatures over the weekend.   Look for the avalanche hazard to increase as new snow, wind and warming temps form new slabs on top of a weak snowpack.

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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.