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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, November 28th, 2015 - 7:00AM
Expires
Sun, November 29th, 2015 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

CONSIDERABLE avalanche danger exists both in the Alpine and at Treeline. Due to a four day rain event wet saturated snow up to 3′ thick could be triggered below 2500′. At higher elevations heavy snow is sitting on top of cold weak snow below making it possible to trigger a large slab avalanche up to 4′ thick on all aspects. Avoid steep slopes and high consiquence terrain features. Careful snowpack evaluation, cautious route finding and conservative decision-making are essential skills if venturing into the mountains today.  

No Rating below Treeline (below 1000′) means there is currently not enough snow to produce an avalanche at this elevation band.    

Special Announcements

DANGEROUS AVALANCHE CONDITIONS REMAIN IN MANY AREAS around Southcentral Alaska.

Due to high avalanche danger the East Hatcher Pass Management Area is closed to public use until further notice. For current information visit DNR Newsroom   and hatcherpassavalanchecenter.org

The search for a missing skier in Hatcher pass continues today. Click HERE for latest media release from the Hatcher Pass Avalanche Center.  

An avalanche was reported yesterday near Anchorage in the Front Range on the Powerline Pass trail. Limited information is known at this time, but warrents extra caution on all hiking trails near steep terrain in Southcentral Alaska.  Click here for observation and photos.        

Sat, November 28th, 2015
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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
  • 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

Over the last three days 4″ of water fell in the form of rain at lower elevations in Turnagain Pass. Rain/snow line fluctuated between 1800’ and 2500’ leaving the snow saturated with water. Several large wet avalanches were observed along the Seward Highway and Portage Valley over the last two days. Warm temperatures will persist today making it possible to trigger a wet avalanche on steep terrain features. Avoid this hazard by choosing low angle terrain away from large slopes and terrain traps. 

*If temperatures drop below freezing this concern will stabilize quickly as water drains and the slab strengthens in the mid elevation zone. 

Debris from a wet avalanche in Portage Valley. This avalanche likely released on the morning of Nov.27th.

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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

Strong Northeast winds topped out at 109 mph on Sunburst weather station yesterday morning. Windslabs over 4’ thick on leeward aspects and crossloaded terrain features are a concern for today in the upper elevation zone. Avoid smooth pillow shaped snow on steep slopes and convexities. Even small features if steep enough could break well above you and have plenty of volume to bury a person. Obvious clues like shooting cracks and whumpfing sounds may not be present today making this avalanche problem difficult to identify. 

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

In the upper Alpine above 2500’ weak faceted snow that formed during a cold snap has been covered up by 4’ of heavy snow creating an upside down snowpack. Last week observations showed a large variation in the distribution of this weaker snow below. It is likely that Northern aspects will harbor the bulk of this problem, but until more information is gathered much uncertainty exists as to how well this new snow has bonded with the older less stable snow below it. This is just one more high consequence reason to avoid steep terrain today. 

Weather
Sat, November 28th, 2015

A very wet and warm storm passed through Southcentral Alaska leaving the region with above freezing temperatures and high-sustained winds for multiple days. In Turnagain Pass rain/snow line reached 2500′, Easterly ridgetop winds maxed out above 100mph and 4 € of water fell over a three-day period.  

Showery weather in the form of mixed rain and snow is expected today and into the weekend with rain/snow line moving to 1000′. Temperatures will hover just above freezing (32F) and begin to cool slightly by this evening. Easterly ridgetop winds 20-30mph are also expected to depreciate by early evening.  This pattern will continue through the weekend with patches of clear sky at times.  

*Seattle Wx Station wind data is currently not available.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32F   0   1.4   25  
Summit Lake (1400′) 33F   0   0.2 10  
Alyeska Mid (1700′) 34F   0   2.0    13.5

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26F   NE   23   98  
Seattle Ridge (2400′) 28F   *N/A   *N/A     *N/A    
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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.