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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Thursday, March 23rd 2017
Created: Mar 23rd 5:13 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.
2 Moderate Treeline / 1,000'-2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
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The Bottom Line

The avalanche danger is MODERATE on slopes steeper than 35 degrees and at all elevations. Human triggered slab avalanches 1-2+' thick are possible in areas that saw a foot or more of new snow from over the weekend. Triggering fast moving loose snow ‘sluffs’ will also be possible in steeper terrain. There are a few glide cracks out there, limit time underneath them and give cornices a wide berth.

Summit Lake: Read the Saturday Summit Summary HERE.  


Primary Concern

A storm that impacted our region last Sunday/Monday dropped varying amounts of snow throughout our forecast zone. Placer Valley was the winner with 2-3’, Turnagain Pass had 8-14”, Girdwood Valley saw 7-10”, and Summit Lake with 4-6”. This new snow fell on weak old surfaces consisting of near surface facets and buried surface hoar. Over the last few days the new snow has been settling and adjusting as cold weather and light winds have kept this snow mostly loose and unconsolidated. Over the last few days there have been a handful of natural and skier triggered slides and few snowmachine triggered slabs. In Placer/Skookum Valley where the slab is thicker these avalanches have been on steep features proportionate to their terrain size. In Turnagain Pass where steeper slopes have seen heavier traffic, these slabs have been relatively small, and not quite large enough to bury a person. Determining whether the new snow will act as a slab is the current question and will determine what type of avalanche could be triggered. Furthermore, the deeper the new snow the larger the avalanche will be if a slab is triggered - such as in the Placer Valley. Questions to keep in mind today:  

  1. Is the snow loose and unconsolidated or is it becoming 'slabby' with daytime warming on Southerly facing slopes? A slope around noon could be stable only to heat up at 3pm and become unstable, taking out your prior tracks. 
  2. Was the snow affected by the winds during the storm and is it stiffer? Any slope where the new snow is acting like a slab will be suspect for triggering an avalanche. Expect poor bonding to the older/weaker snow below on all aspects. 
  3. What are the consequences of the terrain if I trigger an avalanche? Larger slopes have more potential to propagate a larger avalanche - especially in Placer/Skookum zone where the slab is thicker. Be aware of terrain traps such as gullies, cliffs or trees below you.

This is a possible natural or remote triggered slab on a Southwest aspect near the toe of the Skookum Glacier. Notice the three sledders on lookers left side of the photo for scale. This is a good example of a terrain trap that could catch you by suprise and also shows you the potential of a slab to propagate on a bigger slope. Photo taken on 3/21/17 by Lloyd Tesch.

 

A handful of natural and skier triggered avalanches on Magnum's South face. Photo taken on 3/21/17 by Peter Wadsworth. 

  


Secondary Concern

Triggering loose fast moving ‘sluffs’ will be possible today in steep terrain and could knock you over and be larger than expected. On southerly aspects where a thin sun crust has formed triggering a sluff will be limited.  

Skier triggered sluff on the West face of Magnum from 3/21/17. 


Additional Concern

As always, give cornices a wide berth and minimize exposure under them. 

GLIDE AVALANCHES?  Limit time under glide cracks. There is one on Seattle Ridge, left of the up-track, and some in the Skookum Valley along with others scattered about.

 


Mountain Weather

Yesterday skies were sunny and clear. Temperatures ranged from single digits F into the upper 20F’s below 2000’. In the alpine temperatures remained in the teens F with less fluctuation. Ridge top winds 5-10mph were from the West. 

Today looks very similar.  Daily temperatures may range from 0F into the mid 20F’s during the heat of the day. Valley fog is expected to burn off in the afternoon. Ridge top winds are expected to be in the 5-15mph range and no precipitation is expected. 

This stable and dry pattern is expected through Saturday. The first hint of precip in the forecast will be on Sunday as a Low in the Bering moves towards the Aleutians. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 14  65 
Summit Lake (1400') 12  30 
Alyeska Mid (1700')  19 59 

 

RIDGETOP 24-hour data (6am - 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 12  WSW  12 
Seattle Ridge(2400') 15  variable 

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

Subscribe to the Turnagain Area Avalanche Advisory:

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
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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