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Fri, January 17th, 2014 - 7:00AM
Sat, January 18th, 2014 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is HIGH at all elevations.   Large natural avalanches are likely today.   Rain & snow along with warm temperatures and high winds will make for very dangerous conditions in the backcountry.   Travel in or near avalanche terrain is NOT recommended today.

All of the concerns listed below deserve equal weight in terms of both likelihood and consequences.

Special Announcements

There will be intermittent closures today on the Seward Highway for avalanche hazard reduction work between Girdwood and Seward near mileposts 99, 97, 87, 44, 37, 21.   Motorists should expect delays of up to 45 minutes between 10:00 AM and 3:00 PM.

Updates will be posted on the 511 system.   http://511.alaska.gov/

Fri, January 17th, 2014
Above 2,500'
4 - High
Avalanche risk
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
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
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

The already tenuous snowpack is receiving a significant shock to its system.  Rain began falling up to 2,000’ overnight.  Snow that has fallen since mid December has formed into slabs up to 3 feet in depth.  That slab is now losing strength.  As that slab loses strength it becomes much more likely for weak layers near the ground to awaken and release large avalanches.  Expect entire slopes to avalanche.

Wet slab and wet loose avalanches are possible up to 3,000′ in elevation today.

Avalanche Problem 2
  • 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

Heavy wet snow combined with high winds in the upper elevations will create very unstable conditions within the new snow today.  Freshly formed slabs up to 2 feet in depth will likely avalanche on their own.  High winds will also help to build slabs in areas that don’t normally see much wind (e.g. below treeline and well below typical starting zones).  These slabs have the potential to step down to older weak layers near the ground.  Expect avalanches to pull out across large areas and run long distances.

Additional Concern
  • 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

Weak layers that make up the bottom of the snowpack proved to be reactive yesterday.  Both natural and remotely triggered avalanches were observed.  Even if we took today’s weather out of the equation we would still have dangerous avalanche conditions.  Given today’s weather, the likelihood of triggering an avalanche in these deeper weak layers is rapidly on the rise.  Warm temperatures and rain up to 2,000 feet will help to activate these layers.  Dangerous slabs up to 3 feet in depth are likely to take out large areas today.

Fri, January 17th, 2014

Red flags abound in the weather category today.

Temperatures (F) are first, with current temps (6am):
Center Ridge SNOTEL @ 1,880′: 35
Seattle Ridge @ 2,400′: 30
Sunburst @ 3,812′: 28

Center Ridge had a high overnight reading of 40 deg F.   This is a 10 degree rise in 12 hours.

It is currently raining at Center Ridge with .4 € of water over the past 8 hours, with slightly higher amounts in the Girdwood Valley (.5″ of H2O).   This equates to roughly 5 € of new snow at ridge tops.   This by itself is a modest amount of snowfall in starting zones.   However, let’s take a look at winds.

Sunburst averaging 62 mph out of the East.   Gust to 105 mph.
Seattle averaging 48 mph out of the ESE.   Gust to 82 mph.

Precipitation, temperature and winds are currently combining to create very unstable conditions.

Today expect as much as 12 € of new snow, with 2 € of snow water equivalent.   Freezing level will climb up to ridge top elevation (3,000′).   Ridge top winds will be strong all day, in the 65-70 mph range.

Winds and precipitation should taper off on Saturday.   The pattern will remain active (continuation of precip) through the weekend and into the early part of next week.

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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.