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Avalanche Advisory

Turnagain Area Avalanche Advisory
Sunday, January 27th 2019 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

The avalanche danger remains CONSIDERABLE on slopes above 1,500'. Human triggered slab avalanches between 2 to 5 feet thick remain likely; nine avalanches were triggered yesterday. These slabs can be triggered from the bottom, side or on top of a slope while traveling along a ridge. They have the potential to be large, dangerous and unsurviveable. Additionally, cornices may break farther back than expected and could trigger an avalanche below. 

*Cautious route-finding and conservative decision-making are essential again today. A SPECIAL AVALANCHE BULLETIN remains in effect through the National Weather Service. 

SUMMIT LAKE / JOHNSON PASS:  Dangerous avalanche conditions exist in these regions south of Turnagain Pass. Strong wind, a poor snowpack structure and recent avalanche activity all point to an unstable snowpack.


 Show the Complete North American Avalanche Danger Scale
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Yesterday was an interesting day in the mountains. The snowpack proved to be highly unstable and there were 9 confirmed human triggered avalanches. These were all on the back side of Seattle Ridge. Four of them I was able to witness. These four were along Main Bowl (1st Bowl) and were triggered by two snowmachiners traveling along the ridge; releasing the avalanches one after another while they moved along. The ridge is so broad they could not see the slope below and had no idea they were triggering these slides. To our knowledge, there was no one caught in any slides yesterday. 

Most, if not all, of the avalanches triggered were triggered remotely. This means triggered by a person not on the slope, but instead on the ridge above, to the side or at the bottom. The snowpack is set-up exactly for this situation and we can expect remote triggered avalanches as we move forward. The scary thing is, this set-up can allow someone to inadvertently trigger an avalanche onto themselves from below or onto someone else from a safe location. Something for all of us to keep in mind.

The problem is last week's storm snow fell onto a layer of surface hoar (we are now calling the MLK or 1/21 buried surface hoar). This is a persistent weak layer which is inhibiting bonding between the new and old snow and creating our dangerous snowpack structure. How deep the weak layer and subsequent avalanche will be is dependent upon how much snow fell in that zone. The avalanches yesterday were generally 18" to 3' thick. Although yesterday's activity was all between 2,000 and 3,000', we saw no evidence or anyone traveling in the higher elevations testing those slopes. Hence, all elevations above 1,500' should be suspect. Points to keep in mind if headed out today:

1-  The snowpack will be just as touchy, we need to know what is and isn't avalanche terrain before heading out
2-  The snowpack will be slow to adjust/stabilize with this notorious persistent weak layer 
2-  No obvious signs of instability may be seen, yet avalanches could release easily and remotely
3-  Sticking to lower angle slopes (less than 30 degrees) with nothing steeper above is a great way to avoid these avalanche concerns

 

Slab avalanches in Main Bowl (1st Bowl) triggered remotely by riders moving along ridge. 

 

Two slabs triggered remotely by riders along with a cornice break. The slab on the top of the photo is quite thick, up to 5' at the crown. This area is between Main and Jr's Bowl (1st and 2nd Bowl) Thanks to these folks for clearing off the weather station!

 

Snowpack structure at 2,300', West aspect along Seattle Ridge. Clearly seen is the 'thin gray line' of the 1/21 (MLK) buried surface hoar.

 

Video linked HERE.

 

South of Turnagain - Johnson Pass/Summit Lake zone: poor snowpack structure exists in these areas.  Multiple mid-pack weak layers of facets and buried surface hoar have been found as well as a facet/crust combination in the bottom of the snowpack. See the video below (link HERE) as Don Sharaf shows the recent weak layer reacting as well as an older weak layer. Avalanches triggered in this area could step down into deeper layers creating a much larger avalanche. Although this region received less snow (6-12") last week, the snowpack is still very dangerous. 

    
Don Sharaf with the American Avalanche Institute performs an Extended Column Test in the Silvertip area south of Turnagain Pass. A big thanks to the AAS/AAI Pro 2 avalanche course for their information this week.


Avalanche Problem 2

Cornice

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Cornices have grown and may still be quite tender and teetering on the brink of failure. Give them a wide berth from above and limit exposure underneath them. Any cornice fall is not only dangerous itself, but is likely to trigger a slab avalanche below. 


Mountain Weather

Yesterday:  Mostly clear to partly cloudy skies were over the region. Ridgetop winds were light from the east and bumped up slightly to the 15-20mph range overnight. Temperatures have been near 30F at sea level and the lower elevations, while ridgetops have remained near 20F. 

Today:  Mostly cloudy skies are expected today with a chance for a few snow flurries. Up to an inch of snow could fall tonight. Ridgetop winds are slated to keep climbing and reach the 20-30mph range this afternoon from the east. Temperatures look to remain near 30F at the lower elevations and near 20F along ridgelines.

Tomorrow:  Cloudy skies, increased easterly winds and a chance for a few inches of snow is on tap. Temperatures should remain cool enough for snow to sea level. 

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed. We are currently working to replace it.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 27  59 
Summit Lake (1400') 20  20 
Alyeska Mid (1700') 28  44 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 21  ESE   9 28 
Seattle Ridge(2400') 25  *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
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