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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, January 15th, 2014 - 7:00AM
Expires
Thu, January 16th, 2014 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The general avalanche hazard is MODERATE above and below treeline.   In the upper elevations the hazard will rise to CONSIDERABLE later in the day as new snow falls.   Slabs up to 2 feet in depth could be triggered today in steep wind loaded starting zones.

The potential remains for triggering deeper weak layers in the snow.   Avalanches in the new snow could step down to layers near the bottom of the snowpack, with slab depths over 3 feet possible.

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Wed, January 15th, 2014
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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. Dangerous avalanche conditions. 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

It will be important to pay attention to the following weather factors today:
Snow
Yesterday we found new snow amounts above treeline to be in the 6-8” range.  Snowfall should pick up again this morning across the forecast area.   As much as an additional 6” of new snow will fall in the higher elevations today.  
Wind
Winds overnight blew out of the West (17 mph average with gusts to 50mph). In the higher elevations today winds out of the East and Southeast will help to build isolated pockets of fresh wind slab up to 2 feet on leeward slopes.  Snow will be most reactive on steep slopes and during times of peak precipitation intensity.

Bonding in the new snow was generally good yesterday.  Quick hand shears, pole tests and looking for shooting cracks will allow you to assess how well the new snow is bonding.  If you notice cracks radiating away from you on the surface, this is a sign that the new snow is unstable.  Staying off of steep slopes, especially along ridge crests and above gullies will help in minimizing exposure to avalanches within the storm snow today.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

With our focus on how the new snow is bonding and reacting, it can be easy to forget about the dragon lurking well below the surface.  The weak foundation of the snowpack has been able to adjust to the most recent load.  Continued loading at a relatively slow rate will keep the likelihood of triggering a deeper weak layer on the low end of the scale.  Don’t let lack of action near the surface fool you.  The potential still exists for weak snow near the ground to be reactivated, especially on slopes that are able to produce avalanches in the new snow.  Slab depths up to 3.5’ in depth have the potential to propagate across slopes and do a lot of damage.

Weather
Wed, January 15th, 2014

In the past 24 hours the mountains around Eastern Turnagain Arm have picked up 2-3 € of new snow with .1-.2 € of water equivalent.   Winds have come from a variety of directions averaging 17 mph with gusts to 50 mph.   There was a 6 hour period overnight that saw moderate to strong winds out of the West.   Ridgetop temperatures have averaged in the low 20s F.

Today will bring another pulse of moisture, with up to 6 € of new snow possible by evening.   Winds will be out of the Southeast at 10-20mph.   Ridegtop temperatures will remain in the low to mid 20s F.

A series of strong low pressure systems to our South and West will continue to bring precipitation to the area.   Temperatures will be on the rise as we head towards the weekend.   The next chance for more intense precipitation looks to arrive on Friday.

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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.