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Avalanche Advisory

Turnagain Area Avalanche Advisory
Saturday, February 3rd 2018 5:40 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

A generally LOW avalanche danger exists in the mountains surrounding Turnagain Pass. Although triggering an avalanche large enough to bury a person is unlikely, isolated slabs 1-2’ deep can still be found in very steep or wind loaded terrain. LOW danger does not mean No Danger and evaluating the consequences of the terrain will be important before committing to a slope. Additionally watch for cornices or triggering loose surface snow that can be fast moving and knock a person over. 

In the periphery zones of Girdwood to Portage Valley, and Johnson Pass more caution is advised where a slab could be larger and more connected. 

Check out the Summit Lake Summary HERE. 


 Show the Complete North American Avalanche Danger Scale
1 Low Alpine / Above 2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
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.
Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

We like to think of the danger scale on a continuum and we have inched our way towards LOW in Turnagain Pass. Slope testers (skiers and riders) have been in full force over the last week pushing further into the mountains. There have been a handful of slabs triggered without incident this week and it's not impossible to find unstable snow. Keep the following problems in mind as you travel today. 

Persistent Slab: These slabs have been in places where the snow has been stiffed by wind and are failing on buried surface hoar about 1-2’ deep. Most of the activity has been relatively small, but big enough to take someone for an undesirable ride over a cliff or sweep them into a terrain trap. These slabs could be either soft or supportable to the weight a person and will be located on slopes that are more wind loaded. In fact they may resemble a windslab-type look: smooth pillow-shaped and isolated to a specific terrain feature. In the periphery areas of Girdwood, Placer Valley and Johnson Pass more caution is advised due to slightly deeper snow depths, more sustained winds, and the possibility of a larger slab. Identify terrain traps like gullies, cliffs or rocks below before committing to a steep slope.  

 *Triggering a Deep Persistent Slab is unlikely at this time and has become an outlier.  Due to poor structure (basal facets) that can still be found near the ground in the upper reaches of our terrain, 3000’ - 5000’ zone, it is worth keeping in the back of your mind. At this time cold temperatures and benign weather are helping the stability of our snowpack. 

Loose Snow: In many places the snow is too loose to form a slab and the surface snow ’sluffs’ away with the weight of a person. Expect loose dry snow to be fast moving in steep terrain and don’t be surprised if it knocks you over as it picks up speed. Manage your ‘sluff’ and be aware of the consequences below you.

Cornices: Cornices are unpredictable and can break further back along a ridge than expected. Give these features plenty of space. 

Soft slab triggered remotely on Wednesday along the upper ridge of Eddies. This slab was about 80' wide and slid into very steep Southwest facing terrain below. Photo by George Creighton

 

This is an older wind slab on Raggedtop, Girdwood, and is a good example of where a slab could be more supportable due to stronger winds. Photo by Mike Ausman

 

Loose surface snow and cornices on the Southwest face of Magnum. 

 


Mountain Weather

Yesterday skies were clear and sunny with a temperature inversion, single digits (F) in valley bottoms and low teens (F) near ridge tops. Ridge top winds averaged around 10 mph with some gusts in the 20’s. No precipitation has occurred in over a week. 

Winds are expected to be light from the East (5-15mph) and skies will be clear and sunny. Temperatures look similar to yesterday with slightly warmer ridge top temps, low 20F’s and precipitation is not likely.   

A blocking high pressure system over mainland Alaska is expected to persist through the weekend with continued clear skies, cold temperatures and light winds. The long term forecast is calling for similar weather this week with a possibility of a pattern change mid to late week, but a lot of uncertainty still remains. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 17  63 
Summit Lake (1400') -1  17
Alyeska Mid (1700') 16  50 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 14  ENE  23 
Seattle Ridge(2400') 16  SE  10  25 

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 06, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: ClosedClosed as of 4/27
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

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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