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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Friday, February 20th 2015
Created: Feb 20th 5:44 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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.
0 NO RATING Below Treeline / Below 1,000'
 Show the Complete North American Avalanche Danger Scale
The Hoarding Marmot
The Bottom Line

Today in the Alpine the avalanche danger is CONSIDERABLE where a slab 1-3’ thick is sitting on a weak layer of old snow. This weak layer has been reactive over the last few days and is likely to be triggered on terrain steeper than 35°. Below 2000’ the avalanche danger is MODERATE where a more stable snowpack structure exists.

Weather in the form of high winds will be arriving today as another low-pressure system moves into the Southcentral region.  Precipitation is expected to intensify into Saturday and will likely increase the avalanche danger for tomorrow. 


Primary Concern

Today we will see the first of this weather pattern shift as East winds increase, possibly as high as 30-40 mph along ridgetops. With only a few inches of snow available for transport wind loading could add additional stress to an already reactive weak layer. 

Above 2000’ a weak layer of faceted snow is present beneath a 2’ slab in Turnagain Pass that was laid down four days ago. On Tuesday several remotely triggered avalanches occurred on the South face of Tincan as seen in the photo below. Collapsing has been the most commonly observed (heard) sign as this weak layer adjusts to its load. Over the last few days many test pits have been performed and continue to show propagation potential with moderate results.

In areas outside of Turnagain Pass a similar (SLAB + WEAK LAYER) problem exists. In Summit Lake the average slab depth is closer to 1’ in the alpine. Click HERE to see a video from yesterday at Manitoba. In the upper elevations of Girdwood this slab is estimated to be closer to 3’ thick.

Travel advice today is very simple. Avoid all slope angles greater than 35° including small steep features with terrain traps below. With high winds and poor visibility expected today this should be easy advice to follow. 

This is a view of Tincan's South face as seen from along the Seward Hwy. These three avalanches were remotely trigged on Feb.17, the day after a storm left 2' of snow in the upper elevations of Turnagain Pass. If you look closely you will notice recent ski tracks on Common bowl avoid the steepest convexed rollover. 


Secondary Concern

If winds increase as forecasted today small wind slabs 4-6” could be found at mid elevation near treeline. This is a secondary problem to the persistent weak layer + slab combo described above and travel advice remains the same. 


Mountain Weather

Yesterday skies were sunny and temps reached the low to mid 30’s F at lower elevations. Upper elevations remained slightly cooler with localized light winds 5-15mph from the Southeast.

Overnight temperatures have remained elevated in the low 30’s F at lower elevations and high 20’s F along ridgetops. Winds have steadily increasing 15-35mph out of the Southeast on Seattle Ridge and no new precipitation has been recorded in Turnagain Pass.

Today ridgetop winds are expected to be out of the East (30-40 mph) as another warm low-pressure system moves into the Southcentral region. Temperatures will be in the mid to high 30’s F at sea level, with light precipitation starting this afternoon into the evening. Rain/snow line could be as high as 1500’.

Tonight strong winds (40-50 mph) will continue out of the East in Turnagain Pass. Precipitation will increase with up to an inch of water (rain) expected for Saturday at sea level. Temperatures could reach the low 40’s F and rain/snow line may be as high as 2000’.    

*Seattle Ridge weather station wind data was only available after 3PM on Feb.19. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 31  42 
Summit Lake (1400') 24 
Alyeska Mid (1700') 32  .01  trace  25

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 27  N/A  N/A   N/A  
Seattle Ridge(2400') 28  *SSE  *15  *35 

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: Dec 08, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedRain and snow have fallen in Turnagain Pass this week, but not enough to open for snowmachining. Continue to check back to this site for updates.
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail is expected to 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.


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