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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Thursday, December 22nd 2016
Created: Dec 22nd 5:30 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.
 Show the Complete North American Avalanche Danger Scale
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Special Announcement

***Carter Lake and Snug Harbor areas are now open to motorized use as of Tuesday, December 20th. Please respect other closures across the Forest. The Forest Service is monitoring conditions daily and will open more areas just as soon as there is enough snow to prevent resource damage to underlying vegetation. If you are headed to Snug Harbor and Carter today and please send in an observation if you see any obvious signs of instability.


The Bottom Line

Today the avalanche danger is MODERATE in the Alpine where triggering an isolated wind slab or a slab 1-2’ deep is possible on steep wind-loaded terrain features. Evaluate snow and terrain carefully and manage your terrain choices with safe travel protocols. At Treeline and below the avalanche danger is LOW. Remember to avoid terrain traps where an avalanche of any size could have high consequences.

If you are headed to Summit Lake check out the Saturday Summary and recent Summit observations


Primary Concern

Northwest winds15-20mph are expected in the upper elevations today. With up to a foot of snow available for transport this could easily form shallow wind slabs around leeward features in the upper elevations. A Northwest flow can sometimes cause varying wind directions for Turnagain Pass and its common to see a more Southwest direction in some places. Watch out for hard over soft snow, wind pillows or drifts and be on the look out for obvious signs like cracking and whumpfing sounds. Its also possible that a windslab could step down into an older weak layer within the snowpack. More on this below.

There is plenty of snow available for transport on all aspects. Pay attention as surface conditions change with building winds. Depending on the wind direction this Northern aspect of Magnum could see cross loading today. 


Secondary Concern

The snowpack right now has a variety of weak layers within the top 3’ of the snowpack. A widespread layer of weak faceted snow up to 2' deep is our primary layer of concern and was the culprit in many skier triggered avalanches over the weekend. Two seperate layers of buried surface hoar also exist within the top meter of the snowpack in some places in the alpine, but they haven’t been found everywhere. With that said these layers have presented propagation potential in some test pits this week. Should you see active wind loading today, your extra weight could be enough to tip the balance on a steep unsupported slope. Pay attention for stiff snow over weaker snow and avoid wind loaded slopes where the potential of triggering a dangerous slab avalanche is still possible with our current snowpack set-up. 

Should you go into avalanche terrain be aware of other groups and practice safe travel rituals. Only expose one person at a time, always have an escape zone, and regroup in safe spots. 

 

Digging a quick hand pit and poking your ski pole into the snow are good ways to evaluate the snow as you move. Be cautious around steep slopes if you find hollow snow or stiffer snow ontop of loose snow below. This photo was taken yesterday of very weak faceted snow at 2000'.  

 


Additional Concern

Expect cornices to be sensitive and easy to break off. They also could trigger a slab avalanche below. If you choose to walk a ridgeline today, give these a wide berth and be aware of people below you.

 "Sluff" may also be fast moving on steep protected terrain features where the snow is loose and unconsolidated.  Be aware of terrain features that could have high consequences if knocked off your feet.


Mountain Weather

Yesterday a temperature inversion was the cause of valley fog and cooler air near sea level (single digits F) and warmer air in alpine (low 20F’s.) Skies were partly cloudy, winds were calm and no new precipitation was recorded.

Today Northwest winds are expected to increase this morning to a sustained15-20mph. Temperatures will range from 15-25F today. Skies should be partly cloudy and no precipitation is expected.

Northwest winds should become light early tomorrow morning with a possibility of flurries in the morning. Temperatures are expected to be in the low teens (F) in the alpine and single digits near sea level.

*** Alyeska Midway weather station only had data available from 6am to 10pm on Dec.21st, and Sunburst weather station only had data available from 12pm-7pm on Dec.21st. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 21  27 
Summit Lake (1400') 13 
Alyeska Mid (1700') ***23  ***0  ***0  ***16 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') ***20 ***ENE ***6 ***12
Seattle Ridge(2400') 13  ESE

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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