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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Sunday, February 23rd 2014
Created: Feb 23rd 6:34 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
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Special Announcement

Thanks for all the field observations from the public.  This is a huge asset to inform others of avalanche events and increases our collective knowledge of the snowpack.  Remember, you can use the online form or give us a voicemail using the hotline (754-2369 press star to go straight to voicemail).


The Bottom Line

Areas of CONSIDERABLE avalanche danger exist on recently wind loaded slopes as Easterly winds continue to transport snow at and above treeline. Natural wind slab avalanches are possible and human triggered slabs are likely on any steep slope that has seen wind loading overnight or is currently being loaded today. Slab depths could be up to 3' thick and failing in weak snow above the January melt-freeze layer. These are unmanageable avalanche conditions with the potential for slabs to propagate wider than expected and run full path. 

On all slopes both above and below treeline without wind loading, the danger is MODERATE. In these areas, it is still possible to find and trigger a persistent slab avalanche around 2' deep.


Primary Concern

The Easterly winds that were on the rise yesterday have continued their climb overnight and are expected to level off in the 'strong' category today - which means averages between 26-38mph. There is plenty of loose snow available for transport and yesterday evening slopes were being rapidly loaded. At least two natural avalanches were witnessed on the SW face of Sunburst during the rapid wind loading. One was caught on video, that plus additional details HERE.

Additionally, there was one very interesting avalanche on the SW face of Sunburst that occurred earlier in the day between 12:00 and 1:00pm. It is believed to have been a natural triggered by warming plus minor wind loading. This slide occurred early enough in the day that neither the sun nor the wind was in full effect. In my mind, this shows how close to the tipping point some of these slopes are.

Below is the believed natural from around noon on the SW face of Sunburst (3,700' elevation).  The path just to the left of this slide (partially in view) released 4 hours later, around 5:00pm and is one of the two naturals mentioned earlier.

 

For today, steering clear of steep slopes with recent wind loading will be the key to avoiding this problem. South and West aspects will be the most likely candidates for loading, but due to terrain channeling and cross-loading, all aspects are suspect including rollovers. Not only is a simple wind slab concerning enough, the fact that weak faceted snow exists under these slabs makes them downright dangerous. This is because they have the potential to be 2-3' deep and propagate across bowls.


Secondary Concern

On slopes that are not seeing wind loading there is still the potential for triggering a persistent slab avalanche. Even though it has been over a week since Turnagain Pass has seen measurable snowfall and five days for the Girdwood Valley, we are still seeing human triggered avalanches breaking in weak snow around 2' deep. The most recent slides were from yesterday:

1- Snowmachine triggered slab while climbing a chute in 2nd Bowl
2- Snowboarder triggered slab while descending into 1st Bowl            *Both of these are in the Seattle Creek drainage and details are limited.

On Friday, we had two large persistent slab avalanches occur. These were:

1- Skier triggered by a group ascending the headwall that joins the Magnum and Cornbiscuit ridges  - see photo below with more photos HERE plus a write up by the party HERE (Many thanks to the party for sharing their experience!).
2- Snowboarder triggered slide in Warm-up Bowl in Seattle Creek. This avalanche was reported to have a crown depth of 1-5', width of 300' and running to lower angle terrain.

Image is of the avalanche triggered on the headwall between Magnum and Cornbiscuit (2/21/2014, NW facing and 3,500' elev.)

 

Although time is helping to decrease the likelihood of triggering one of these avalanches, the possibility remains. Many folks have been able to ski, snowboard and ride steep terrain without a problem - this is the hard part and why these avalanches are a roll of the dice right now. At the end of the day, it comes down to personal risk threshold. If you choose to hit the steeps, safe travel practices will help to hedge your bets. If you do not want to deal with a potentially life changing avalanche, then recreating on slopes less than 35 degrees with nothing steeper above you is the ticket. 


Sun and warming:
Due to the wind, sunshine today will likely have a hard time warming the surface snow above treeline. This includes the sun crusts on southerly aspects left over from yesterday. However, if you do find a sheltered area with enough warming, persistent slab potential will increase along with sun induced point release avalanches. Keep an eye out for any south facing start zone that is seeing intense sun, little wind and dampening surface snow.


Mountain Weather

Overcast skies turned mostly clear by the afternoon yesterday allowing for some welcome sunshine. What was not as welcome were the winds that gradually increased from the East / Northeast over the course of the day. Hourly averages were in the 20's mph with gusts in the 30's. Temperatures were on a steady rise as well with daytime highs on the ridgelines in the upper teens to 20F and the low 30'sF at 1,000. Overnight, the wind has continued its slow climb and temperature is generally holding steady.

Today will be a blustery, but clear, day in the backcountry. We are currently sitting with a dominant ridge of high pressure to our Northeast and a set of low pressure centers to our South and West. Winds should continue to squeeze through these features from the East with ridgetop averages around 30-40mph. Temperatures are forecast to remain mild, in the mid to upper teens on ridgetops and around 30F at sea level. 

Tomorrow, Monday, this pattern persists with moderate to strong East winds, mostly clear skies and slowing warming temperatures. However, looking forward to Monday night and Tuesday a chance for a inch or two of snow is possible as a small embedded low pushes into Southcenteral. For the mid-week, models are still showing a more significant warm up.

 

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 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
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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