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Avalanche Advisory

Turnagain Area Avalanche Advisory
Sunday, January 21st 2018 5:31 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

MODERATE avalanche danger exists on all aspects above 2,500' for triggering a very large slab avalanche between 3 and 8+' thick. These dangerous avalanches are more likely to be found at the high elevations, above 3,000' and though tough to trigger, have very high consequences. Additionally, loose snow sluffs are getting faster and larger by the day and be aware of cornice falls along ridgelines. There is a LOW danger below 2,500' where triggering an avalanche is unlikely.


 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.
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

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

It has been 4 days since a very warm storm slammed into our area dropping inches of rain up to 2,500'-3,000' and several feet of snow above this. Since then, cold temperatures have cemented the wet snow into place and locked up any slab avalanche problem below 2,500' and 3,000' in areas. Therefore, our main concern lies at elevations above this where a 'deep persistent slab' problem exists. On these upper elevation slopes, a dense hard slab is sitting on a variety of weak layers in the mid pack (buried surface hoar) and old November facets near the ground. Triggering a deep slab will be more and more difficult as the days pass, but still possible. The most likely spots to trigger them are thin areas in the snow cover, often near rocks, or where the slope rolls over. High peaks, that see a lot of wind, can also be thinner and more likely to find a deep slab.

If you are headed out today, and the skies stay clear enough for easy travel above treeline, keep these points in mind:

-  This is 'low probability, high consequence' situation - often refered to a 'Scary Moderate' avalanche danger
-  Several tracks may be on a slope before someone finds a trigger spot
-  
Obvious signs of instability are not likely to been seen (such as whumpfing and cracking)
-  Remote triggering is possible 
-  This issue can simply be avoided by sticking to terrain below 3000’ (which is a good portion of terrain at Turnagain) or choosing low-consequence terrain in the alpine.

 Photo: Old cornice fall and avalanche from 1/16 near the Seattle Headwall region at 3,300'. Steep upper elevation slopes that have not slid are the ones most suspect for triggering a large slab avalanche.


-


Avalanche Problem 2

Dry Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Loose snow sluffs are rocketing down steep slopes as this cold weather continues to loosen and facet the surface snow. If choosing large steep terrain, watch your sluff. At mid elevations where 4-8" of loose snow sits over a hard crust, sluffs are still likely and although not deep, will run quite far. 


Additional Concern

Cornice

Cornices have grown with the last storms, many have fallen, yet many have not. As always, give these features a wide berth and remember they can break further back than expected. A cornice fall at the high elevations could trigger a large avalanche on the slope below.


Mountain Weather

Mostly sunny skies with thick mid-elevation and valley fog filled the area yesterday. Temperatures were chilly, generally in the teens at all elevations. Overnight temperatures have dropped into the single digits in many valley bottoms and mid-elevation locations. Winds over the past 24-hours have been light and variable.

Today, we should see a slow climb in temperatures as light Easterly flow brings clouds and a chance for snowfall. By late today, an inch of snow is possible at all elevations (including sea level). Overnight, another 2-4" is possible, again at all elevations. Temperatures are slated to climb into the upper teens at most locations. Winds are expected to be 5-10mph from the Northeast.

Tomorrow, Monday, light snowfall is possible, but little accumulation is expected. Skies also may clear a bit. Winds look to remain light and temperatures will be on a downward trend. 

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 12  54 
Summit Lake (1400') 10  15 
Alyeska Mid (1700') 15   43

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 14  NE  12 
Seattle Ridge(2400') 10   N calm  16 

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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