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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, January 3rd 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 triggering a large slab 2+’ thick in steep terrain. Give cornices a wide berth and avoid being under glide cracks. Natural glide avalanches are possible today and could release without warning.

There is LOW avalanche danger below 1000' where a surface crust has strengthened the snowpack.

SUMMIT LAKE / JOHNSON PASS / LYNX DRAINAGE:  South of Turnagain Pass, keep in mind old buried weak layers exist and there is potential for triggering a large slab avalanche that breaks near the ground.


 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

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

UPDATE: We just recieved a report of a large remote triggered avalanche in the Seattle Creek drainage that occured yesterday. We don't have much info at this time and its unknown what layer this avalanche failed on. We do know that remote triggered avalanches are a sign of a persistent slab problem and it may be buried surface hoar. Keep this new info on your mind if you're heading to Turnagain Pass.  

Cooling temps and light winds are helping to improve stability of wind slabs since the New Year’s storm dumped 2-3’ of snow and blasted our snowpack with hurricane force winds. Clear and sunny weather today will make it easy to identify smooth pillowed convexities, cross-loaded gullies, and hollow sounding snow – wind slab habitat. What makes this avalanche problem challenging is it’s transition into becoming a persistent slab. As this storm snow problem strengthens, a layer of buried surface hoar from Christmas remains on our minds. Hand pits yesterday were challenging to find this layer due to how deeply buried (2+’) it is in places. Many observations over the last week have been documenting the location of buried surface hoar and its presence and reactivity have been variable. With that said – triggering a wind slab on a mid-storm density change or on buried surface hoar are both possible today.

If you’re headed out, ease into steeper terrain with a conservative mindset. Evaluate terrain and snow as you travel and remember ‘whumpfing’ is an obvious clue of instability.

CORNICES:  There are some very large cornices along many ridgelines across our region. Triggering a cornice with the weight of a person or snowmachine is possible today. Remember these can break further back than expected. Give cornice features lots of space and avoid being directly under them.

 

A storm triggered slab from the New Years storm below Hippy Bowl on SW aspect of Tincan. Also note the wind sculpted snow in the alpine and cornice along the ridgeline.  

 


Avalanche Problem 2

Glide Avalanches

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Glide cracks exist in popular ski and snowmachine terrain and a may be tricky to identify with new snow covering them. Several glide cracks have avalanched this week and it’s possible more will release in the coming days. The best way to manage this problem is to avoid being under slopes with cracks opening up. They can release at any time and are not typically associated with human triggers. Glide avalanche have occurred in Lynx Creek, on Lipps, and Seattle Ridge this week.

 

 

A glide avalanche on Lipps SW face that released just before the New Years Storm is not covered by new snow and looks very different

Photo of Lipps glide crack taken yesterday (1-2-19). Although part of this crack has released the additional portion can still avalanche without warning.  

 


Additional Concern

Persistent Slabs

South of Turnagain:  A shallow and poor snowpack structure exists in the Summit Lake zone. Buried weak layers of facets associated with crusts sit near the base of the snowpack. An observation from Lynx Creek on Friday also found a reactive layer of facets mid-pack. Keep in mind Summit Lake has received additional loading from the New Years storm - strong winds and a foot of new snow. Recent avalanche activity and ‘whumpfing’ will be good reminders to keep terrain choices conservative in these zones. Triggering a larger avalanche that releases near the ground is not out of the question. Check out the Summit observations HERE for the more snowpack details.


Mountain Weather

Yesterday: Snow showers were observed in the morning with a trace of new snow at Turnagain Pass. Rain/snow line was near 300’. Light to moderate ridgetop winds from the East shifted to a NW direction by mid-day. Temperatures cooled in the upper elevations to low 20F’s/upper teens (F) as skies cleared in the afternoon. 

Today: A cooling trend will continue today as a high-pressure system establishes itself over Southcentral, Alaska. Expect temps at 3000’ to reach low teens/upper single digits today. Temperatures near sea level will drop into low 20F’s to teens by this evening. Northwest ridgetop winds will be in 5-15mph range. No precipitation is expected.

Tomorrow: A similar pattern of clear skies, cold temps and light NW winds will continue into the weekend.

*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') 25  trace  63 
Summit Lake (1400') 23  22 
Alyeska Mid (1700') 25 0.12  50 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 16  NW  26 
Seattle Ridge(2400') 21  *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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