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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, January 4th 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 in the Alpine and Treeline zones for Turnagain Pass. Triggering a slab avalanche 2-3’ thick is possible and could be large enough to bury or kill a person. Natural glide avalanches are possible today and could release without warning. Give cornices a wide berth and avoid being under glide cracks.

SUMMIT LAKE / JOHNSON PASS / LYNX DRAINAGE: South of Turnagain Pass, keep in mind multiple buried weak layers exist and recent avalanche activity from the New Years storm was significant. More potential for triggering a large slab avalanches exists in this zone.  


 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

In Chugach State Park and Hatcher Pass dangerous avalanche conditions have been reported this week. Check out the Hatcher Pass Avalanche Information Center mid-week summary click HERE and recent observations from the Front Range HERE.


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Yesterday we received a report of a remotely triggered large slab avalanche in Warm-Up Bowl of Seattle Creek. This avalanche was triggered by a snowmachine from Seattle ridge without incident the day before (Wednesday.) The weak layer in question was confirmed to be buried surface hoar. We have been tracking this layer since it formed on Christmas Eve and have found its size and distribution to vary across the region with no consistent pattern.  This is a tricky problem to manage. Multiple people could ride or ski a slope before someone finds a pocket or just the right trigger spot. The incident on Tuesday is proof that this layer is reactive and a slab could be large enough to bury or kill a person. Obvious clues like whumpfing may not be present. Digging a test pit adjacent to a slope may or may not be representative of the presence or reactivity of this weak layer.

As we move away from the New Years Storm that brought hurricane force winds and 2-3’ of snow, we must be diligent with our terrain choices and travel protocols. This means avoiding terrain traps, identifying safe zones and traveling one at a time in avalanche terrain. 

South of Turnagain:  The New Years storm caused some notable avalanche activity throughout Summit Lake on many West and South aspects. This isn’t a big surprise. Observers over the last month have been tracking a poor snowpack structure in this region. Buried weak layers of facets associated with crusts sit near the base of the snowpack and buried surface hoar has also been found similar to Turnagain Pass. The Lynx Creek and Johnson Pass area are also suspect for deeper instabilities and also warrants a cautious mindset. Evaluate terrain and snow as you travel and remember ‘whumpfing’ and recent avalanches are obvious clue of instability.

 

Remotely triggered avalanche on a North aspect of Warm-up Bowl in Seattle Creek that occured on Wednesday. Photo taken yesterday by Wendy Wagner. 

 

 

Crown profile of Warm-up bowl avalanche. 

 


Avalanche Problem 2

Glide Avalanches

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Several glide cracks have avalanched over the last few days and we expect more to release through the weekend. Glide cracks have been seen in popular ski and snowmachine terrain and some are covered by new snow from the New Years storm. If you see a glide crack the best way to manage this problem is to avoid traveling under them. They can release at any time and are not typically associated with human triggers. Known glide avalanches have occurred on Lipps,  Seattle Ridge, Penguin Ridge,  Lynx Creek and Johnson Pass this week.  

There are also some very large cornices along many ridgelines across our region. Give them lots of space and similar to glide cracks avoid being directly under them.

This glide crack on Lipps continues to release chunks of the slab. Photo taken yesterday.  


Mountain Weather

Yesterday: skies were clear and sunny. Temperatures dropped from the low 20F’s into the single digits throughout the day at Turnagain Pass. Areas near the coast remained in the 20F’s most of the day. Westerly Ridgetop winds were light, 5-10mph. No precipitation occurred.

Today: Expect clear and sunny skies in the alpine with valley fog. Temperatures will be slightly inverted with cooler air (single digits) at lower elevation and in the teens F near ridgetops. Winds should remain be calm to light from the West.

Tomorrow: An arctic high is positioned over mainland, AK and will continue to bring cold, clear and dry conditions through the weekend. Expect temperatures to range from single digits to teens.

*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') 15  62 
Summit Lake (1400') 21 
Alyeska Mid (1700') 16  48 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 15  19 
Seattle Ridge(2400') 15  *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: Mar 22, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Open
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: Open
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Open
Lost Lake Trail: ClosedClosed as of 3/22. Unfortunately HEAVY rain over the past week has washed much of the snow off the lower stretches of this trail.
Primrose Trail: OpenPlease stay on trail to avoid resource damage through forested areas.
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: Open
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
Summit Lake: Open

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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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