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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, February 16th 2018 4:57 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger is MODERATE above 1,000' on all aspects. Triggering a slab 2+ feet deep remains possible. Watch for active wind loading, and be aware of shallow wind slabs on leeward slopes and cross-loaded gullies. Additionally, weak layers deeper in the snowpack may still be triggered, creating a larger avalanche. Evaluate snow and terrain carefully.

The avalanche danger below 1,000' is LOW where triggering an avalanche is unlikely, but not out of the question. Be aware of terrain traps where pockets of unstable snow may be lurking. 

**If you are headed to Placer Valley, remember that very little snowpack information exists in this zone. Ease into terrain with caution and be aware of other groups in the same area. If you see or experience any avalanche activity please take a picture and send us an observation HERE. 


 Show the Complete North American Avalanche Danger Scale
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.
Special Announcement

Placer river and Carter Lake zones open to snowmachines today.  The Alaska Railroad reminds us that crossing railroad tracks in the Placer Valley is okay but it is illegal to ride down tracks.  Please avoid the active ARR construction site at the Luebner Lake outflow. 

Tomorrow, Saturday, Feb 17th, from 11am-12:30pm - Free Avalanche Beacon Practice with CNFAIC! This is a short workshop on how to effectively perform avalanche companion rescue. Open to all users and skill levels. Alaska Mining and Diving Supply is providing a free lunch and the event is a chance to pay tribute to Christoph Von Alvensleben and Jeremy Stark, who lost their lives in an avalanche, 10 years ago, on Feb. 15th, 2008. 


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering a persistent slab avalanche 2' deep remains possible across the region, and winds today may add additional stress. Several weak layers including widespread buried surface hoar (from Jan. 21) sits roughly 1-2' below the surface. A person skiing or on a snowmachine may tip the balance and initiate a larger slab avalanche. Triggering a smaller wind slab or a cornice may also activate this layer. The snowpack is now at a point where no signs of instability are likely to be present before one of these avalanches is triggered. Assessing the terrain and the potential outcome of an avalanche breaking deeper in the pack is key. Are there terrain traps below you? Cliffs? Are your partners watching and rescue ready? 

Winds this weak have loaded some slopes and scoured others as seen yesterday on Seattle Ridge. Triggering a soft or hard persistent slab is possible with our current snowpack. 


Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering an isolated wind slab is possible today and will be more likely in places where wind is actively transporting snow into steep terrain. Today Northwest winds may be moving loose snow along some ridgetops and forming new wind slabs on leeward features. Earlier in weak ridgetop winds loaded some slopes and scoured ridge lines. Pay attention to where the snow feels stiff, looks pillowed, sounds or feels hollow and watch for shooting cracks.  Hard wind slabs tend to break when you are out onto the slope and often fracture above you. Be aware of wind loading patterns in the terrain, especially cross-loaded gullies. Sometimes Northwest winds can funnel in from the South near Sunburst and on the Southern end of Turnagain Pass. 

Small wind slab triggered in the last few days on a wind loaded gully, SE aspect of Seattle Ridge at about 2300'. 

 


Additional Concern

Deep Persistent Slabs

Deep Persistent Slab: Above 3,000' in the Alpine zones, several old weak layers of facets and buried surface hoar sit near the ground and in the mid-pack. This structure is most pronounced in areas with a thin overall snow cover, such as the South end of Turnagain Pass and the Summit Lake area.  As you plan your day, keep in mind that there are deeper persistent layers that could 'wake up' if you find the wrong spot.


Mountain Weather

Yesterday was clear and sunny with no precipitation. Westerly winds became Easterly 5-15mph early afternoon. Temperatures along ridgetops were in the high teens (F) increasing to the low 20F’s during the heat of the day. Temps at sea level bumped into the high 20F’s and back into the teens F’s overnight. Patches of valley fog were present near Turnagain Arm.  

Mostly cloudy skies are forecasted for today. Temperatures should average in the 20F’s and dip down into the teens (F) overnight. Ridge top winds will start out light from the East, but will transition to the Northwest and increase to 15-20mph. No precipitation is expected. 

Clear skies are in the forecast for Saturday wth similar temperatures. Moderate Northwest winds will continue tomorrow, becoming light by late afternoon. Increasing clouds and warmer temperatures are expected Sunday evening into Monday with a possibility of a few scattered showers.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 26  64 
Summit Lake (1400')  17 24 
Alyeska Mid (1700') 23  58 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 18  W--E  22 
Seattle Ridge(2400') 21 W--E  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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