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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Kevin Wright  
Wednesday, March 27th 2013
Created: Mar 27th 6:29 am
2 Moderate Alpine / Above 2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
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The Bottom Line

The recent snow storm on Monday gave us enough snow to worry about backcountry stability.  After a look around yesterday, we found mostly stable snow with pockets of stiff slab with a reactive character.  Today's danger rating is MODERATE for specific areas of stiffer wind slab which sits on top of loose powder.  South facing slopes are also a greater concern with buried sun crusts that have shown to be reactive over the last 5 days.  


Primary Concern

The storm on Monday dropped 12-15 inches of snow in some parts of Anchorage.  You can expect to find similar amounts in the Turnagain forecast region, with Girdwood getting a little more in the areas we've surveyed.  A notable feature of this storm was the cold temperatures.  The snow fell cold and dry, making for a light density powder with low water content.  Despite only moderate wind during the storm, the light powder was easily moved around by wind.  There are a lot of wind affected slopes, varying from scoured surfaces on one aspect, to stiff wind slab, to sheltered pockets of loose powder.  

Today, the wind slab is my greatest concern.  Yesterday we found a couple pockets of stiff supportable wind slab that collapsed with a "whoomph" when we skied across (see pit profile and description here).  Given a steep enough slope, this would probably initiate a small avalanche.  Furthermore, the problem can be even worse if it sits on top of a sun crust.  The two things I would actively try to avoid today - stiff wind slab on steep slopes, and southerly aspects where reactive sun crusts may be found.  

If you can avoid these two issues, there are still pockets of good quality loose powder to be found.


Secondary Concern

The recent stretch of sunny weather produced 2 specific weak layer concerns.  

1.  Sun crusts on south aspects.  We found at least 3 distinct buried sun crusts yesterday, with the top one being moderately weak with a tendency to propagate.  A number of smaller skier triggered avalanches have been reported in the last week, and the majority seem to be on southerly slopes, probably because of the sun crust layers.

2.  Non sun affected slopes simply got weaker in the surface snow during the 2 weeks of clear weather.  Weak snow by itself isn't necessarily a problem, until you get stronger or stiffer snow on top of the weak snow.  


Mountain Weather

Following the snow storm two days ago, the weather turned cold and sunny.  Last night it got even colder, with temperatures dipping into the negatives.  There is a mild temperature inversion, making the mountains slightly warmer than the valleys.  

Temperatures at 6am

Portage valley -15 degrees

Turnagain Pass Center ridge 2.7 degrees

Summit Lake -7.3 degrees

Alyeska, top chair 6 is 4 degrees

We had no measureable precipitation yesterday and wind was light from the north at most of the weather stations.  
Today's weather looks fairly tame if you can deal with the cold.  Incoming in the next few days is a larger storm system with warmer temperatures and more precipitation.


Graham will issue the next advisory tomorrow morning, March 28th.

 

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).

Winter snowmachine use open/closed status and riding conditions updates

Riding status is not associated with avalanche danger. An area will be open to motorized use in accordance to the Forest Management Plan when snow coverage is adequate to protect underlying vegetation. Backcountry hazards including avalanche hazard are always present regardless of the open status of motorized use areas.

(Updated: May 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur. This advisory provided by the Chugach National Forest, in partnership with Friends of the Chugach National Forest Avalanche Information Center.


USFS SNOW AND AVALANCHE HOTLINE (907) 754-2369
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