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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, February 26th, 2013 - 7:00AM
Expires
Wed, February 27th, 2013 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Continued light snowfall and strong wind overnight keeps us at the upper end of MODERATE in the backcountry today.   Expect to find wind driven snow above treeline with areas of triggerable wind slab and a slight possibility of natural avalanches in some areas.   Below treeline, some areas may have a buried reactive crust layer.  

Special Announcements

Placer/Skookum and 20 mile are now OPEN to snowmachines, with adequate snow cover in those areas.   Watch for areas of thin snow cover, open water, and other hazards that you won’t find at higher elevations.   The avalanche center staff have not been to this zone yet, so we can only speculate on the snowpack at this time.  

There will be intermittent road closures on the Seward Highway for avalanche hazard reduction work on Tuesday February 26, 2013 between Girdwood and Portage (MP89-82).   Motorists should expect delays of up to 45 minutes between 8:30AM and 10:30AM.   Thank you for your patience.

Tue, February 26th, 2013
Alpine
Above 2,500'
2 - Moderate
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. 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

Even light snowfall adds up over time and can become a probelm.  About 6 inches have fallen in Turnagain Pass and Girdwood in the last 24 hours.  Overnight wind was strong enough to transport quite a bit of snow.  Yesterday the surface snow up high was getting a “slabby” feel.  Even without any prominent weak layers, recent loading has the ability to build pockets of avalanche potential. 

Last night there was a natural avalanche reported near Kern creek just south of Girdwood that was large enough to affect the railroad.  This underscores the potential for more avalanches to happen despite only moderate amounts of new snow.  High wind yesterday played a large role in causing this avalanche.

Wind loading at higher elevation will be the most likely place to find trouble today.  Expect deeper and stiffer snow on west aspects with cross loaded north and south facing slopes. 

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

A series of ice crusts with associated weak layers have kept us thinking about the lower to mid elevation snowpack.  A couple days ago forecasters found collapsing and unstable pit results at 1200 feet elevation.   As we open the low elevation zones of Placer/Skookum and 20mile to snowmachines, this should be a concern to think about.  

The Placer/Skookum/20mile zones are poorly understood at this time due to a lack of information.  Expect to find moderate avalanche danger, but remember that those zones get different weather patterns and local variations may be found.

Weather
Tue, February 26th, 2013

The last few days have been consistent light snowfall with wind up high.   Yesterday and overnight new snow built to around 6 inches at mid elevations in Girdwood and Turnagain, and double that amount in Grandview.   Wind has gusted 40-50+ mph every hour since yesterday morning at Sunburst.   Temperatures have been in the 20s at high elevation to mid 30s at sea level.  

Expect more of the same weather today.   A large low complex south of Kodiak is affecting our region with snowfall across the gulf coast spilling over to Turnagain Arm.   Total precip will be a little less than yesterday and wind may diminish slightly as well.   The forecasted snow doesn’t look like a big addition to the avalanche danger, but reduced visibility may hamper our ability to see very much today.  

Graham will issue the next advisory tomorrow morning, Feb 27th

Observations
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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.
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