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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, February 13th 2019 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 2000'. Triggering a small wind slab will be possible on steep, leeward terrain features due to active wind loading. There is also still a chance of triggering a large slab avalanche 2-3' thick on slopes 35 degrees and steeper. Give cornices a wide berth, avoid travel under glide cracks.

SUMMIT LAKE / JOHNSON PASS: Areas south of Turnagain Pass harbor a thinner, weaker snowpack with multiple weak layers present including the MLK buried surface hoar. Similar strong winds will be impacting this area today. Choose terrain wisely and look for signs of instability.


 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.
Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Today strong Northwest winds 20-30mph with gusts in the 40Fs will impact our region. This wind direction can create unusual wind loading patterns opposite our normal Easterly storm track direction. Expect drifting snow in the mid and upper-elevations where 4-6” of loose faceted snow is available for transport. Hard supportable snow should be suspect. Shooting cracks will be an obvious sign that steeper slopes could have tender wind slabs. Although wind slabs are likely to be shallow, they could be more dangerous if they were to step-down and trigger a large slab that breaks in the MLK buried surface hoar.


CORNICES: Cornices are looming large in some of the Alpine terrain. Give them an extra wide berth as they often break farther back than expected.

Yesterday afternoon Westerly winds were seen transporting snow along many ridgetops and some mid elevation zones. Silvertip Creek drainage, 1pm Feb.12, 2019

 


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

The last human triggered avalanche on the MLK buried surface hoar occurred a week ago on Eddies. That avalanche was a 2'-3' deep and was triggered remotely from the ridge on a steep, unsupported slope. Over the last week many people have been pushing into steeper terrain without incident. Strong winds will be transporting snow onto leeward aspects today. Wind loading has the potential to add additional stress to the snowpack. The question is what could tip the balance? Could wind loading do it or would it require a person or snowmachine? Lots of old tracks may still be visible or partly covered, but this doesn’t necessarily mean the slope is safe. Several tracks may be on a slope before someone finds a trigger point and the whole slope avalanches. Sastrugi, wind eroded snow, on ridgelines could also harbor poor structure due to the widespread nature of the MLK buried surface hoar. Thus remote triggering is still a possiblity.

As winds change the overlaying slab, keep the MLK surface hoar in mind and remember:

1- This weak layer is widespread in the region and seems to be particularly suspect between 2000'-2500' due to a melt-freeze crust associated with it.

2- Use safe travel protocol. Expose only one person at a time (this includes paying attention to other groups in the area), watch partners, stop in safe zones and be rescue ready.

3- Wind loaded steep features, large connected and unsupported slopes are the most suspect. As always, one can simply avoid high consequence terrain and stick to slopes under 35 degrees with nothing steeper above to avoid the issue.

Yesterday, Feb.12, 2019 on Twin Peaks several test pits showed propagation. The weak layer involved  was the MLK buried surface hoar and melt freeze crust. Facets were also associated with this layer. 


Additional Concern

Glide Avalanches

There was a glide release observed on Monday (2-11-19) in Girdwood on the lower southern shoulder off of Goat Mtn. Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time.  Look out for glide cracks and limit exposure under them. Several popular routes in Turnagain Pass, Lipps and Magnum's South aspects, have large glide cracks that are hard to see from below and challenging to avoid. 

Glide avalanche released sometime between the evening of Feb.10th and the morning of Feb.11. Photo courtesy of B. Veatch. 


Mountain Weather

Yesterday: Skies were mostly sunny. Temperatures near sea level were in low 30Fs dropping to mid 20Fs overnight. Temperatures at ridge tops were in mid 20Fs dropping into the teens F overnight. Northwest winds were 10-20mph increased to 15-30 with gust in upper 30mph’s to low 40’s. No precipitation was recorded.

Today: Skies will be mostly sunny. Strong Northwest outflow winds at ridge tops and in Gap Valley’s will be 15-30 mph with gusts in 40mph’s. Temperatures at sea level will be in the low 20F’s. Temperatures near ridge tops will drop from mid teens to low teens F.

Tomorrow: Clear skies, cooling temps and offshore winds will continue Northwest winds 15-30mph should start to decrease Thursday afternoon. Temperatures will continue to fall into the single digits. No precipitation is expected.

Strong offshore winds expected region wide for Southcentral, Alaska

*The Seattle Ridge anemometer (wind sensor) was destroyed. We have a replacement on the way and it should be operational by mid February.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 27  58 
Summit Lake (1400') 25  25 
Alyeska Mid (1700') 27  50 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 17  NW  35 
Seattle Ridge(2400') 24  *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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