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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, December 28th 2018 7:00 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’ for triggering an unstable cornice or a new/old wind slab.  Triggering a slab on an older layer 2+’ deep is becoming less likely, but not impossible in the periphery of the forecast zone near Johnson Pass and Silvertip.  Identify glide cracks and avoid traveling under these unpredictable avalanche hazards.

JOHNSON PASS / LYNX DRAINAGE / SUMMIT LAKE:  South of Turnagain Pass weak layers exists under 2-3' of snow. Human triggered slab avalanches over 2' thick are possible on slopes over 35 degrees.

LOST LAKE:  This zone is out of the advisory area, but is also suspect for harboring weak layers 2-3' below the snow surface due to recent reports. Pay attention for signs of instability like collapsing and recent avalanches. 


 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

For the Hatcher Pass Avalanche Center mid-week summary click HERE.


Avalanche Problem 1

Cornice

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Cornices remain large and looming along many ridgelines of our forecast zone. On Sunday and Monday evidence of natural cornice fall was observed and several human triggered cornices were reported. The best way to manage this hazard is to give cornices a lot of space and avoid travel directly underneath them. Approach ridgelines with caution and be aware of groups traveling in the same zone as you who could inadvertently triggered one from above.

WIND SLAB: There is plenty of snow available for transport and we may see winds pick up into the 20’s mph later in the day. There is a layer of buried surface hoar below 2-5” of new snow from the last few days and this may become our next weak layer. Today keep an eye out for drifting snow and shooting cracks. These are signs of fresh wind slab development. Triggering an older wind slab is becoming pretty unlikely at this point, but not out of the question in very steep terrain. A period of strong winds on Christmas has created some stiffer pockets of snow in the Alpine. 

Large cornices still intact on the SW facing terrain of Magnum. This photo also has some natural cornice fall observed on Mon (12.24) as well as glide cracks opening up in the lower right corner. 

 

A thin layer of surface hoar lays below a few inches of snow accross our forecast zone and will be a suspected weak layer if winds pick up and form wind slabs. 


Avalanche Problem 2

Glide Avalanches

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

The most recent glide avalanches observed were in Lynx Creek drainage on Monday. Numerous glide cracks have been slowly opening up around our region including commonly traveled areas like the SW aspect of Sunburst and Corn Biscuit, and in Warm-up (-1) Bowl on Seattle Ridge. It is important to remember glide cracks can release into full-blown avalanches at any time and are not associated with human triggers. The best way to manage this problem is to keep your eyes peeled for cracks and limit travel underneath them.

Glide crack in Warmup (-1 Bowl) on the North facing slope. This is a common crack that forms and has been known to release. Photo taken on 12.24 by Wendy Wagner.

 


Additional Concern

Persistent Slabs

If you are headed to areas south of Turnagain, keep in mind triggering a large slab avalanche is still possible. Buried weak layers, roughly 2-3' below the snow surface, have been found in the Summit Lake zone and as far south as Lost Lake. Numerous observations this week in Turnagain Pass have been finding a stable snowpack in the older November snow near the ground. Some uncertainty remains around Johnson Pass, Lynx Cr drainage and Twin Peaks/Silver Tip where the snowpack often transitions to a shallower structure similar to Summit Lake. Observations in Summit Lake over the last few weeks have been finding facets associated with several crusts near the ground with reactivity in stability tests. The most recent avalanche activity in this zone was observed last week (Dec.20) where some of these avalanches stepped down to older layers within the snowpack. Should you head into the periphery of our forecast zone evaluate the snowpack and terrain as you travel, and keep your senses alert for any whumpfing -- an obvious clue for triggering a slab avalanche.


Mountain Weather

Yesterday: Skies were obscured and snow showers left a few inches of new snow (1-3”) across our region. Temperatures decreased into the low 30Fs near sea level and mid 20Fs at 1000’. Ridgetop winds remained light from the East shifting to the North overnight as skies cleared.

Today: Expect partly cloudy skies in the morning becoming mostly cloudy by the afternoon. Snow showers are expected by late afternoon and into the evening with 3-7” possible overnight. Ridgetop winds should start out calm and could increase to 10-25mph from the East by the afternoon. Temperatures should be similar to yesterday and remain cool enough for snow at sea level.

Tomorrow: Snow flurries will taper off in the morning with another break between snow showers. We may see another period of partly cloudy skies before another storm moves into our region on Sunday through Monday. There remains some uncertainty around how much precipitation, but expect a period of warmer temperatures and increased winds.

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 27  .1  55 
Summit Lake (1400') 26  .1  13 
Alyeska Mid (1700') 26  .27  37 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 20  ENE  19 
Seattle Ridge(2400') 25  *N/A  *N/A   *N/A  

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, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of 4.3.19
Placer River: ClosedClosed as of 3.20.19 due to lack of snow.
Skookum Drainage: ClosedPlacer access closed as of 3.20.19 due to lack of snow.
Turnagain Pass: ClosedClosed as of 5/6. Thanks for a great season all, see you next winter!
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Closed
Lost Lake Trail: ClosedClosed as of 3.22.19 due to lack of snow
Primrose Trail: ClosedClosed as of 4.3.19 due to lack of snow
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: ClosedClose as of 5.1.2019
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
Summit Lake: Closed

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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.


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