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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Aleph Johnston-Bloom  
Wednesday, January 6th 2016
Created: Jan 6th 4:09 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.
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

Today the danger at Treeline and above Treeline is MODERATE. The likelihood of triggering a Wind Slab avalanche 2-4’ deep is possible above 1000’. These slabs are most likely to be triggered on steep leeward slopes. Large fresh cornices loom above much of this same terrain and should be avoided. For the periphery of the core Turnagain advisory zone (Girdwood Valley and south towards Summit Lake) where the overall snowpack is thinner elevated caution is advised. There are still buried weak layers that have been reactive and could produce a Deep Slab avalanche.

Human triggered avalanches are possible today. Don't let the sunshine effect decision-making. Identify steep terrain and areas of concern, evaluate the snowpack carefully, watch for signs of instability and practice safe travel techniques.

Below 1000' the danger is LOW


Primary Concern

With sustained winds averaging in the mid-50’s mph on Sunday (and gusts to 101mph on Sunburst)  2-4' thick wind slabs are possible on steep leeward slopes, particularly above treeline; though it is worth recognizing that strong winds such as these have a tendency to load slopes far below ridgelines, creating a mid-slope avalanche problem. There was significant cross-loading as well. Identifiying where the winds deposited the snow is crucial. Look for pillowed snow, listen for hollow sounds and pay attention to stiff snow under your skis, snowboards or snowmachines. Watch for shooting cracks and remember even a small pocket of wind slab in steep terrain can have high consequences. Wind slabs are notorious for letting you travel out onto them and then breaking above you. Evalute carefully before commiting to steep terrain from above or below.


Secondary Concern

Sustained winds, relatively warm temps and moist snow have continued to grow large cornices.  These have the potential to fall naturally or be triggered by the weight of a person or machine and can be very dangerous. Travel under or on them should be avoided. They have the tendency to break farther back from the ridge than expected and can trigger an avalanche on the slope below by adding a lot of weight quickly. As you approach ridgelines and the entrances to backcountry bowls make sure you aren't accidently traveling on overhanging snow. 


Additional Concern

In some parts of the advisory area now sitting under 5-7' of settled storm snow is a layer of old faceted snow on top of the Thanksgiving Rain Crust. This still needs to be a consideration as you travel into the backcountry today. This is a low probability, very high consequence set-up.  It is important to use safe travel practices and do not overload slopes with multiple skiers, boarders or snowmachines. Limiting your exposure time spent underneath large paths such as those that effect areas like Johnson Pass and the Lynx Creek drainage.  In addition we have limited snowpack information from Johnson Pass and Lynx Creek but we know that the snowpack is shallower. The surface hoar that developed prior to Christmas may be buried and preserved especially near the creek. Watch for signs of instability: recent avalanches, shooting cracks, collapsing and whumpfing. Pay attention to snow depth and trigger points. Deep slabs are most easily triggered from shallow spots where the weight of the traveler can more easily effect the weak layer. 

NOTE:  In areas such as Summit Lake, the snowpack is shallower and harbors more weak layers under the recent storm snow.  See Wendy’s observation and write-up from a snowboarder-triggered avalanche (Saturday) that failed on a buried surface hoar layer that ran on a mellow (28-30 degree) slope.

 


Mountain Weather

The stormy weather moved out yesterday, skies cleared and winds died down. The winds were Easterly in the morning 15-25 mph, gusting in the 50's and then shifted to the west and have been light overnight. Temperatures were in the mid 20Fs at ridgeline and 30Fs at 1000'.  There was a cooling trend overnight. 

Today will be mostly clear and sunny as we have a break inbetween storms. Temperatures will be in the mid 20Fs to mid 30Fs. Winds will be light and Westerly. The clouds will build again this evening and there is chance of snow showers overnight and tomorrow. The next Low is forecasted to move into the Gulf and effect the forecast area into the weekend. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 30  85 
Summit Lake (1400')  27 0 0  27
Alyeska Mid (1700')  32 0 0  32

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 24  ENE  15  56 
Seattle Ridge(2400') 25   n/a n/a  n/a 

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: Mar 28, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: OpenPlacer remains open but SKOOKUM DRAINAGE will close to motorized use on April 1st.
Skookum Drainage: OpenSKOOKUM DRAINAGE CLOSES TO MOTORIZED USE ON APRIL 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: Open
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: Open
South Fork Snow River Corridor: Open
Summit Lake: Open

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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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