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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, December 27th 2018 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

MODERATE avalanche danger remains for triggering a cornice or a wind slab avalanche in terrain above 1,000'. Identify ridgelines with cornice features and give them a wide berth. Pay attention to changing weather, shooting cracks or blowing snow – these will be obvious clues wind slabs are touchy. Glide cracks are still opening and releasing, minimize exposure under them. Keep in mind that limited visibility could make navigating these hazards challenging today.

JOHNSON PASS / LYNX DRAINAGE / SUMMIT LAKE:  South of Turnagain Pass weak layers exists under 2-3' of snow. Human triggered slab avalanches over 2' thick are possible on slopes over 35 degrees. We have limited information from Johnson Pass and Lynx Creek and would love any info from these areas. Consider submitting an observation .

LOST LAKE:  This zone is out of the advisory area, but is also suspect for harboring weak layers 2-3' below the snow surface due to recent reports. Triggering large slab avalanche should be on your radar here as well. Pay attention for signs of instability like collapsing and recent avalanches. 


 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

For the Hatcher Pass Avalanche Center mid-week summary click HERE.


Avalanche Problem 1

Cornice

Several inches of new snow (2-6”) is possible today and ridgetop winds are expected to be light. Should you see more snow than forecasted or an increase in winds be ready to adapt to any changing weather. Storm slabs are unlikely unless we see over 6" of new snow.

CORNICES: Today new snow may obscure visibility. Having some familiarity of known cornice hazards is helpful, but even so, it could be challenging to see them today. Earlier in the week cornices were quite active. A few close calls occurred on Sunday where several people triggered large cornices including one person who went for a ride without any reported injury. Two days ago we saw a period of strong winds and this may have added more weight to some already large cornices. Give cornices a lot of space and be aware of groups traveling in the same zone as you who could inadvertently triggered one from above.

WIND SLABS: Triggering a lingering wind slab is possible on steep leeward terrain features. A period of strong winds on Tuesday formed shallow wind slab that may be on weak snow or buried surface hoar. Feel for denser snow on top of loose snow that feels upside down and be weary of supportable hollow sounding snow.  Although winds are expected to be light, don’t be caught off guard if you see any sign of blowing snow or shooting cracks. These will be obvious clues wind slabs are tender.

This photo is from Monday (12-24-18) and is a good example of how difficult it is to see cornices until you're too close. This cornice fall triggered a wind slab pocket below. Photo by Wendy Wagner.

 


Avalanche Problem 2

Persistent Slabs

If you are headed to areas south of Turnagain, keep in mind triggering a large slab avalanche is possible. Buried weak layers, roughly 2' below the snow surface, have been found in the Summit Lake zone and possibly as far south as Lost Lake. We suspect the snowpack may be similar around Johnson Pass, Lynx drainage and Twin Peaks/Silver Tip. These weak layers are composed of facets associated with crusts and have been showing signs they could be reactive enough a person could trigger a large avalanche. Listen and feel for whumpfing (collapsing of the snowpack) and evaluate terrain for consequences before selecting a route to travel. 


Additional Concern

Glide Avalanches

Evidence of two glide avalanches (actual releases, not just cracks) were observed in the Lynx Creek drainage on Monday. Numerous glide cracks have been opening up in more commonly traveled areas of our forecast zone including the SW aspect of Sunburst and Corn Biscuit, and in Warm-up (-1) Bowl on Seattle Ridge. It is important to remember glide cracks can release into full-blown avalanches at any time and are not associated with human triggers. The best way to manage this problem is to keep your eyes peeled for cracks and limit travel underneath them.

Photo taken yesterday (12-26-18) of glide cracks on the SW face of Corn Biscuit. Photo by Andy Moderow. 


Mountain Weather

Yesterday: Skies were overcast. Temperatures were in the mid 30F’s at sea level. Freezing line was near 1000’ and temperatures at ridgetops were in the low to mid 20Fs. Ridgetop winds were light to moderate from the Northeast. No precipitation was recorded.

Today: Cloudy skies and a 2-6” of snow (0.37 Snow water equivalent) is for forecasted today. A slight cooling trend will help bring rain/snow line from 1000’ to just above sea level (200’) by this evening. Temperatures at 1000’ will be in the low 30Fs to upper 20Fs. Expect ridgetop winds to by light 5-15mph from the East.

Tomorrow: A period of clearing skies is expected overnight through tomorrow morning with another chance for scattered snow showers Friday evening into Saturday. Temps will be in the mid to upper 20Fs at 1000’ and rain/snow line may be right around sea level. Easterly ridgetop winds will be light to moderate. 

*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  56 
Summit Lake (1400') 30  12
Alyeska Mid (1700') 31  34 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 22  ENE  28 
Seattle Ridge(2400') 27  *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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