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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, March 23rd 2018 6:01 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 1000'. Triggering a large, destructive slab avalanche 2-4+ feet thick is possible on all aspects and may be remotely triggered. Watch for wind slabs along ridgelines and avoid cornices. Pay attention to afternoon warming. Evaluate snow and terrain carefully. 

Below 1000’ avalanche danger is LOW where a stout surface crust has formed. 


 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

Heads up in the Eagle River area and North to Hatcher Pass  where strong winds this week have triggered many large and destructive natural avalanches. Check out our observations page HERE for information about avalanche activity over the past week region-wide.  


Avalanche Problem 1

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering an deep slab avalanche 2-4+ feet thick remains a scary possibility. Strong Northwest winds that ended Thursday morning loaded a variety of aspects and scoured many ridge lines.  Shaded aspects (North to Northeast) may be more loaded with this unusual wind direction. All aspects are suspect due to well preserved and widespread buried surface hoar and facets under a thick, connected slab 2-4+ feet thick. A thin sun crust on solar aspects may soften in the afternoon with the sun and remember daily warming in the mid 30F’s can make it easier to trigger a slab. Our current hard-pack snow conditions are deceiving and may give the appearance of ‘stable snow’. Knowing where in the terrain a large and destructive avalanche could be triggered is a difficult question. It may be the 10th person onto the slope that finds a thin part of the snowpack (a trigger point) or it could be a person triggering a slab remotely on an adjacent slope or below. This was the case on Tuesday in Girdwood when a helicopter remotely triggered an avalanche from 1/4 mile away. There is a lot of uncertainty around this avalanche problem and just how stubborn it will be to trigger now that winds have mellowed out. 

With a deep slab problem it is important to remember no signs of instability may be present before a slope releases.  Thin spots near rocks and along ridgelines are likely trigger points. Take a moment to visualize the consequences if the slope does slide. How far would a very large avalanche run in this terrain? Are there terrain traps below?   

Natural avalanche on a NE aspect of Raggedtop was first noticed Tuesday morning and is a good example of the size and distance a very large avalanche could run. 

 

An avalanche triggered Tuesday in Girdwood near Notch Mountain at 2500'. This slab was 3-6' deep and failed on facets on top of a slick crust, bed surface. 

 

 


Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Wind Slabs: Wind slabs have formed on a variety of aspects due to unusual loading patterns and cross loading from strong Northwest winds this week. Smooth supportable surfaces where the snow is hollow sounding are suspect, especially if the slope is unsupported. Look for cracking and identify terrain features with a pillow-shaped look where triggering a wind slab could break above you. Warming from the sun can make triggering easier in the afternoon, and a wind slab could step down to older snow and create a much deeper and more dangerous avalanche.

Cornices: Cornices are large and looming and the sun and above freezing temperatures can make them more unstable. Give cornices lots of space and limit exposure underneath them.  

 

Northern aspect of Magnum with recent wind loading from several days of strong NW winds. In Turnagain Pass this wind direction can funnel through some terrain from the South and load Northern aspects. 


Mountain Weather

Yesterday skis were clear and Northwest winds were to 5-15mph. Day time high temperatures near sea level were in the mid 30F’s and overnight dipped into the teens F. Upper elevation temperatures became slightly inverted - with temperatures increasing from low teens (F) yesterday morning to mid 20F’s overnight. No precipitation was recorded. 

Today expect skies to remain clear and sunny.  Winds will be light and variable. Daytime temperatures may reach the mid 30F’s in the upper elevations and low 40F’s at sea level. Overnight temperatures will drop back into the teens F at all elevations. 

Saturday will be partly cloudy with light winds similar daily temperatures (15F - 35F.) Sunday will be overcast as Low pressure moves into our region with the first chance for precip Sunday evening into Monday. At this point precipitation type and amounts are uncertain. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 21   0 80 
Summit Lake (1400') 14  32 
Alyeska Mid (1700') 20  75 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')        
Seattle Ridge(2400')        

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: Dec 01, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed
Placer River: ClosedClosed
Skookum Drainage: ClosedClosed
Turnagain Pass: ClosedClosed November 21 due to inadequate snow conditions. #hopeforsnow
Twentymile: ClosedClosed
Seward District
Carter Lake: ClosedClosed
Lost Lake Trail: ClosedClosed
Primrose Trail: ClosedClosed
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: ClosedClosed
South Fork Snow River Corridor: ClosedClosed
Summit Lake: ClosedClosed

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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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