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Avalanche Advisory

Turnagain Area Avalanche Advisory
Sunday, December 23rd 2018 7:00 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

There is a MODERATE avalanche danger for slopes above 1,000'.  Triggering a wind slab avalanche or breaking off a cornice will be possible in areas exposed by yesterday's winds. Wind slabs could be 1-3' thick and composed of hard snow, allowing a person onto them before releasing. Glide cracks are opening and could release at anytime, watch for cracks and avoid being under them.

JOHNSON PASS / LYNX DRAINAGE / SUMMIT LAKE:  South of Turnagain Pass proper weak layers exists under 2-3' of snow. Human triggered slab avalanches over 2' thick are possible on slopes over 35 degrees. We are currently gathering as much information from these areas and please consider submitting a report if you head there - thank you!

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. Triggering large slab avalanche should be on the radar here as well. 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

Hatcher Pass avalanche conditions: Make sure and check out Hatcher Pass Avalanche Center Saturday morning forecast HERE if headed this direction.


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

With so much loose powder snow from the Solstice Sleeper Storm blanketing the mountains, yesterday's winds were like an unwanted Christmas guest. The Sunburst weather station reported just over 24 hours of sustained NE winds in the 20-30+ mph range with the strongest gust at 60mph at 11am. Although winds quieted down overnight, we can expect to see a bit of damage today. Wind slabs, wind crusts, scoured zones, and hopefully many areas that were saved from the wind. Temperatures have dropped to the upper 20'sF at sea level, freezing the wet snow at lower elevations. 

Limited visibility yesterday made it difficult to assess the extent of natural wind induced avalanche activity. We can expect there were some cornice falls and wind slabs that released. We did see one of these in the Summit area on Tenderfoot (photo below) - a cornice fall that triggered a wind slab. Today, wind slabs are likely to be hard (do to the warm temperatures) and could allow a person onto them before releasing. Watch for shooting cracks and be especially aware of the terrain - where will someone go if a wind slab knocks us off our feet? 

CORNICE FALLS:  Cornices have grown and could be teetering on the brink of failure, give them a wide berth as they can break off further back than expected. They could also trigger a wind slab or larger avalanche below, creating an even bigger problem. 

 

Difficult photo, but this is a small cornice fall that triggered a small wind slab below in the Summit Lake area on Tenderfoot Ridge (Dec 22)


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Buried weak layers roughly 2' below the snow surface have been found in areas south of Turnagain Pass, such as Johnson Pass, Lynx drainage, Twin Peaks/Silver Tip, the Summit Lake zone and Lost Lake. These layers are composed of facets associated with crusts and have been showing signs they could be reactive enough a person could trigger a large avalanche. For the first time yesterday, we found these layers not to be reactive, which is a good sign but this is only one data point and not something to hang our hats on. If you are headed to areas south of Turnagain, keep in mind triggering a large slab avalanche is possible. Listen and feel for whumpfing (collapsing of the snowpack) and look for avalanche activity from the storm that may have steeped down into the deeper layers.

This is a snowpit from the Summit Lake area on Tenderfoot yesterday. Snow height was 4'. The top 1' is the recent storm snow that had significant wind effect above treeline. This is the first pit we've had that did not show failure in the facet/crust combinaiton. 


Additional Concern

Glide Avalanches

As visibility improves, keep a close eye out for opening glide cracks. These are likely to be oozing down the slopes with all the new snow weighing the snowpack down. Glide avalanches can release at any time and are not associated with human triggers. It's a case of not wanting to be in the wrong place at the wrong time. We knew of many cracks opening up on the SW faces of Tincan and Sunburst as well as the Johnson Pass area and Gold Pan in upper Bertha Creek. 

Location of known glide cracks on Sunburst - under the weather station near Taylor Pass. Photo from Dec 11th.


Mountain Weather

Yesterday:  Mostly obscured skies and intermittent snow showers were over the region yesterday. Favored areas saw up to 4" of new snow (Girdwood Valley and the north end of Turnagain Pass), while many areas only saw a trace to and inch. Ridgetop winds blew in the 30's mph with a gust to 60 midday before quieting down significantly overnight to less than 10mph. Temperatures were in the mid 20'sF along ridgelines and 32F at 1,000.

Today:  Partly cloudy to obscured skies will be over the area. Valley fog could set in when skies begin to clear today or tomorrow. Ridgetop winds are forecast to remain light and variable and temperatures mild, mid 20'sF along ridgetops and 30F at 1,000'. 

Tomorrow:  Partly cloudy to sunny skies are on tap Christmas Eve as we continue with a break between storms. Temperatures look to cool slightly (around 32F at sea level) and models are showing another chance for a few inches of snow for Christmas Day. 

*Seattle Ridge weather station is rimed over and not recording any data. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 31  0.2  64 
Summit Lake (1400') 30  16 
Alyeska Mid (1700') 31  0.2  37 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  NE  23  60 
Seattle Ridge(2400') *N/A  *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.


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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