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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, November 24th, 2012 - 7:00AM
Expires
Sun, November 25th, 2012 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

We are issuing advisories 5 days a week through November on Sat, Sun, Tue, Thur and Fri.

BOTTOM LINE

Cold temperatures and no significant precipitation in several days is leading to a slow decrease in the avalanche danger.  Pockets of stiffer slab over very weak facets at the ground still create the avalanche recipe in specific places.  Conservative terrain management is still advised.  Below treeline is generally LOW avalanche danger.  

Sat, November 24th, 2012
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
  • 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

If I could relabel the icon on the left as “Persistent Weak Layer”, it would tell the story a bit more accurately.  Faceted snow at the ground is still the culprit, but the overlying snow is also slowly rotting away in our colder temperatures.  This means the former slab over the persistent weak layer is degrading into “weak layer over weak layer”.  Everything is faceting, getting weaker, and losing the potential to propagate into destructive avalanches.  Check out a pit profile from yesterday HERE.

However, we are still finding pockets that will collapse or “whoomph” when you set your own skin track.  This indicates enough of a stiffer slab component to collapse as a unit.  Any areas that show this sign should be considered for avalanche potential.  We found whoomphing on the lee side of a wind loaded ridge yesterday, which convinced us to go elsewhere.  We know that recent avalanches have happened without human influence.  Despite evidence of better stability, I’m not ready to tell myself that I can outsmart the current problem.  

The best way to manage terrain this weekend is to monitor slope angles and keep it less than 35 degrees.  All the recent avalanche activity (HERE, HERE and HERE) has happened on steeper slopes, so this should be an effective strategy.  The picture below shows 2 recent avalanches on Sunburst, and illustrates the terrain that is likely to harbor more avalanche potential.  

Weather
Sat, November 24th, 2012

We continue to be locked into a clear and cold weather pattern.  A 30 degree temperature inversion is showing on weather stations this morning, with comfortable temperatures in the 20s at the ridgetops.  Weather models are showing some kind of pattern change early next week.  


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).  

Wendy will issue the next advisory Sunday morning, November 25th.  

Observations
Recent Observations for Turnagain Pass
Date Region Location
02/27/24 Turnagain Observation: Seattle Ridge
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02/21/24 Turnagain Observation: Tincan Trees
02/21/24 Turnagain Observation: Sunburst
02/20/24 Turnagain Avalanche: Tincan
02/20/24 Turnagain Observation: Seward Highway across from Johnson Pass TH
02/19/24 Turnagain Avalanche: Base of Seattle Ridge
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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.