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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, January 2nd 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 CONSIDERABLE above 1000' where triggering a slab 2-4' thick is likely on slopes steeper than 35 degrees. Give cornices a wide berth and avoid being under glide cracks. Natural glide avalanches are possible today and could release without warning. Cautious route-finding and conservative decision making are essential.

 

MODERATE avalanche danger exists below 1000' where triggering wet loose snow is possible in Portage Valley. This problem will become unlikely if cooling temperatures create a surface crust.

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
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.
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.
Special Announcement
  • Be aware of dangerous avalanche conditions in the Anchorage Front Range/Chugach State park. Several avalanches have been reported over the last few days. Click HERE for details.
  • Parking may be difficult along Turnagain Pass. Please be aware of parking safely and avoid blocking unplowed lots as DOT crews work to clear roads and parking areas.

Avalanche Problem 1

Storm Slabs

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Unlikely

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Very strong winds and 3+' of new snow over the last three days has created a variety of storm related avalanche problems. Wind slabs may range from 1-4+' thick on leeward and cross loaded features and may be located further down slope than expected. Feel for denser snow on top of weaker snow and be wary of pillowed or hard supportable snow that rolls into steeper terrain. In places where storm slabs may be less wind affected, this snow may also be upside-down with denser snow on top of weaker snow. Surface hoar from last week was buried under this new storm snow and its unknown how these persistent weak layers are adjusting. The size of an avalanche will depend on the size of the terrain, the larger and more connected the slope the more potential for a larger avalanche. Obvious signs like whumpfing and cracking may or may not be present until it’s too late. Remember its only been 24 hours since 70+ mph winds and heavy precipitation were falling. This is your first red flag of the day. 

Storm totals (6am Dec.31 - 6am Jan.2)

  • Turnagain Pass: 25” (2.4” SWE)
  • Summit Lake: 12” (1.0” SWE)
  • Girdwood (Alyeska Midway): 27” (2.3” SWE)

CORNICES: High winds and blowing snow will have added to already large cornices. These may be very sensitive, and a cornice fall could trigger a large avalanche on the slope below. Remember these can break further back than expected.  

 Cross loading and some natural storm triggered slabs on specific terrain features was observed in between storms on Monday at Tincan. 

 

Buried surface hoar found in a pit on Monday was 14" below the surface. Expect this layer to be at 2-4' below the surface in some places.  


Avalanche Problem 2

Glide Avalanches

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Chance

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Under all this new snow are hidden glide cracks. They are looming over popular ski and snowmachine terrain and 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.

Most recent known glide avalanche was seen on Monday on an East facing slope of Seattle Ridge near Bertha Creek. 


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 and this area is also suspect. Summit Lake did receive strong winds the last few days as well as a foot of new snow at road level, likely more in the alpine. Do not forget the possibility of triggering a larger avalanche that could release near the ground. Check out the Summit observations HERE for the most current information. 


Mountain Weather

Yesterday: Strong Easterly winds decreased from 50mph yesterday morning to 15-30mph for the remainder of the day. A wintery mix of rain and snow was observed along Turnagain Pass with rain/snowline around 900’. Several additional inches of snow fell yesterday following an intense period of heavy snow and rain before 6am. Temperatures hovered around 32F at 1000’ and ridgetops were in the mid 20F’s.

Today: Skies are expected to be mostly cloudy with scattered snow showers and a few inches of new snow possible. Rain/snow line is expected to drop in elevation from 500’ this morning to sea level by this afternoon with cooling temperatures. Expect temperatures near sea level to drop into the mid 20Fs overnight and teens in the mid elevations. Ridgetop winds from the East will be moderate 10-25mph transitioning to light from the Southwest later in the day.

Tomorrow: A cooling trend is expected tomorrow as high pressure moves into our region through the end of the week. Expect clearing skies and temperatures to continue to drop into the single digits.


*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') 31  0.1  66 
Summit Lake (1400') 33  0.4  22 
Alyeska Mid (1700') 31  0.16  51 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  ENE  17  74 
Seattle Ridge(2400') 28  *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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