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Avalanche Advisory

Turnagain Area Avalanche Advisory
Saturday, February 17th 2018 4:50 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 where triggering an isolated wind slab or larger slab 2 feet deep remains possible. Be aware of radiation from the sun adding additional stress to solar aspects. 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. Avoid terrain traps where a pocket of unstable could have high consequences. 

The Summit Lake area has seen recent natural activity. Read the Summit Summary 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

Be aware of dangerous natural and human triggered avalanche activity in Hatcher Pass this week. Yesterday three people were caught and one person buried in a large human triggered avalanche. Luckily everyone is okay. If you’re headed North check out the Hatcher Pass avalanche forecast HERE.

TODAY, Saturday, Feb 17th, from 11am-12:30pm - Free Avalanche Beacon Practice with CNFAIC! We will be hosting a short workshop on how to effectively perform a companion rescue at the motorized parking lot. Open to all users and skill levels. Alaska Mining and Diving Supply is providing a free lunch and the event is also 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 up to 2' deep remains possible across the region, and a sunny Saturday may increase the odds. Several weak layers including widespread buried surface hoar (from Jan. 21) sits roughly 1-2' below the surface. New snow combined with periods of strong ridgetop winds have created both soft and hard slabs on a variety of aspects. Be extra cautious on solar aspects and if you see moist surface snow or point releases near rocks, these are obvious clues the sun is adding stress to these aspects. Unfortunately obvious signs of instability may not be present today and all aspects are suspect due to poor structure. Assessing the terrain and the potential outcome of an avalanche breaking deeper in the pack is key. If you find yourself in a crowded area, consider changing your objective or waiting for people to clear a slope before continuing. 

 

Jan. 21st buried surface hoar  is ~2' below the surface and continues to show propagation potential in stability tests. Snow pit at 2700' on Tincan on a West aspect.  

 

A photo of some of the wind affected terrain near Squirrel Flats. Little snowpack information exists in Placer Valley/Skookum area. If you see or experience any avalanche activity please take a picture and send us an observation HERE

 


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 on all aspects and will be more likely in steep terrain. Earlier in the week moderate to strong winds (from a variety of directions) loaded some slopes and scoured ridgelines. 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.  Wind loaded convexities and cross-loaded gullies facing the sun are most suspect. 

Recent natural wind slab from earlier in the week in Zero Bowl, NW aspect of Seattle Ridge. 


Additional Concern

Deep Persistent Slabs

Above 3,000' in the Alpine, 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 places 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 a trigger spot in a shallow area. 


Mountain Weather

Yesterday was mostly cloudy with light Westerly ridgetop winds and a brief period of moderate Westerly winds this morning. Temperatures in the upper elevations were in the high teens/low 20F’s and sea level temps bumped into the high 20F’s during the day and teens F’s overnight. 

Sunny clear skies and light Westerly winds are expected today.  Daily temperature swings should average in the upper 20F’s today and dip down into the teens (F) overnight. No precipitation is expected. 

Sunday will range from party to mostly cloudy with daily temperature swings in the low 20F’s to low 30F’s. Light winds will shift from the West to an Easterly direction. A similar pattern is expected through Monday followed by the possibility of warming trend starting Tuesday. However at this point low confidence remains in the long term forecast. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 22  64 
Summit Lake (1400') 13  24 
Alyeska Mid (1700') 20  57 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 19   7 25 
Seattle Ridge(2400') 22  NW   17

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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