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Avalanche Advisory

Turnagain Area Avalanche Advisory
Saturday, December 29th 2018 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 is MODERATE above treeline where increased winds last night may have formed sensitive wind slabs on lee aspects. Any fresh wind slab found is likely to be soft and shallow, yet could be easy to trigger. Cornices are still a concern and likely grew with last night's wind. Glide cracks are moving! Please keep a close eye out for these brown cracks and limit travel underneath them. 

SUMMIT LAKE / JOHNSON PASS / LYNX DRAINAGE:  South of Turnagain Pass, weak layers of facets have been found 1-3' below the surface. These layers are suspect to be difficult to trigger but not out of the question. If someone hits the right spot, a large avalanche may result. Heads up in these thinner snowpack zones.


 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.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Special Announcement

Hatcher Pass:  Problems remain in the snowpack at Hatcher Pass, please check this recent observation of a remote triggered avalanche yesterday and HPAC's Saturday morning forecast HERE if headed this way.


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

A few inches of new snow plus some strong wind overnight and we can expect to see pockets of wind slabs today. These are likely to be soft, shallow and found above treeline where the easterly winds have been blowing. Over the past few days, several inches of new snow has accumulated with an additional 2-4" overnight at the higher elevations. Winds have decreased this morning and another 2-4" of snow is forecast for today. This new layer of snow could obscure the wind effect from last night - so we'll need to be on our guard for hidden wind slabs if skies clear enough for travel into the Alpine.

Quick hand pits and feeling for stiffer snow over softer snow are good ways to check for wind slabs or any other surface instability. A couple thin layers of buried surface hoar from the past several days intermixed in the soft surface snow may make any wind slab that forms more touchy. 

CORNICE FALLS:  There could still be large cornices that are close to breaking off and only need a person's weight to tip the balance. Many cornice falls were reported last week and they continue to grow slowly with recent snow and wind. Continue to give them a wide berth and limit exposure under them. 

 

A new crop of small surface hoar seen yesterday (photo Trip Kinney). There is another layer of buried surface hoar 4-6" deep in soft snow that was buried on Christmas. We are tracking these layers, as they could develop into future weak layers when the next real snow storm hits.


Avalanche Problem 2

Glide Avalanches

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Glide cracks are moving - beware. These can release at anytime and are most suspect when we have proof to their movement, as seem below. Cracks are littering the slopes in Lynx Creek drainage and one released on Corn Biscuit in the last couple days. Others we know of are on the SW aspect of Sunburst, Corn Biscuit, Warm-up (-1) Bowl on Seattle Ridge and the SW face of Magnum. Check out this link for more information on glide avalanches. The best way to manage this problem is to keep your eyes peeled for cracks and limit travel underneath them.

 

Glide cracks moving on SW facing Magnum Ridge (Thamm, Moderow)


Glide avalanche on Corn Biscuit, seen and photographed on 12/28 by Andy Moderow.

 Glide crack in Lynx Cr. This crack is SW facing. (photo: Graham Predeger) 


Additional Concern

Persistent Slabs

South of Turnagain: keep in mind triggering a large slab avalanche is still possible. Buried weak layers, roughly 2-3' below the snow surface, have been found in the Summit Lake zone. There is some uncertainty around Johnson Pass, Lynx Cr drainage and Twin Peaks/Silver Tip where the snowpack transitions to that with poorer structure as found at Summit Lake. A report from Lynx Ck yesterday found a buried layer of facets reactive (but stubborn) in the snowpack. Observations in Summit Lake over the last few weeks have been finding facets associated with crust reactive in stability tests. The most recent avalanche activity in this zone was observed last week (Dec.20) where some of these avalanches stepped down to older layers within the snowpack. Should you head into the periphery of the forecast zone, evaluate the snowpack and terrain as you travel. Listen for whumpfing -- an obvious clue for triggering a slab avalanche.


Mountain Weather

Yesterday:  Clear skies gave way to overcast conditions yesterday as a small storm moved in during the evening hours. Around 2" of new snow fell at the mid-elevations and likely up to 4-5" and at the upper elevations. Ridgetops winds picked up last night from the east into the 20's mph with gusts up to 40mph and have quieted down this morning. Temperatures warmed with the snowfall and have been in the 20'sF along ridgetops, 30F at 1,000' and mid 30's F at sea level. 

Today:  Snow showers are likely to continue through the morning, adding an additional 2-4" of snow (possibly a rain/snow mix for sea level). Skies may clear up this afternoon and snowfall cease as the system heads north. Ridgetop winds are expected to remain relatively light, 5-15mph from the east. Temperatures should stay near 32F at sea level, 30F at 1,000' and in the mid 20'F along ridgelines. 

Tomorrow:  Another more powerful system looks to impact the region Sunday. This will be the first in a series of storms that are expected to bring snow, wind and rain to sea level through Monday. Stay tuned!

*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') 28  0.2  54 
Summit Lake (1400') 25  0.1  13 
Alyeska Mid (1700') 27  0.2  37 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 20   ENE 15  40 
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.


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