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Avalanche Advisory

Turnagain Area Avalanche Advisory
Sunday, February 24th 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 is MODERATE on slopes over 35 degrees above 2,000'. Triggering an older wind slab resting on weaker faceted snow is possible. Slabs could be anywhere from 4" to 2' thick depending on prior windloading. Steep rocky terrain will be the most likely place to find one of these avalanches. Additionally, sunshine with warm temperatures may cause wet sluffs on steep southerly terrain. As always, give cornices a wide berth and limit exposure under glide cracks.

GIRDWOOD / PORTAGE / PLACER:  Old wind slabs could be deeper, up to 2' thick. 

SUMMIT LAKE / JOHNSON PASS:  Triggering a larger, more dangerous slab remains a concern due to various old weak layers in the mid and base of the snowpack. Conservative terrain choices and a cautious mindset is advised if choosing to venture into the further reaches of this area.

SEWARD / LOST LAKE:  Old wind slabs up to 2' in depth could be found and triggered in this area on steep windloaded slopes.


 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
  • Take a minute out of your day to help the Community Snow Observations crew with gathering snow depth information in Alaska!! Website is communitysnowobs.org. It's easy to do, you just need a smart phone, 30 seconds and your probe to measure the snow depth.
     

Avalanche Problem 1

Persistent Slabs

Almost Certain
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Unlikely

Chance

Historic
Very Large
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Small

Size

After quite the pummeling by the outflow winds last week, the snowpack has had a couple days to rest under clear skies and light winds. As we head into today and into the work week, the quiet weather is expected to remain, allowing the snowpack to continue to adjust and stabilize. We have not heard of, or seen, any avalanche activity since Thursday when the NW wind event wreaked havoc. This event triggered large natural avalanches in the Summit Lake area on the Kenai as well as some other areas along Turnagain Arm and in the Portage Valley. The snow surface above treeline is a mixed bag of sastrugi, scoured areas, wind drifts, wind crust and wind slabs. That said, many areas are reported to still harbor soft fun snow and escaped the brunt of the damage. 

The avalanche issues today revolve around older weak layers within the snowpack (persistent weak layers). The most recent weak layer was buried a week ago and sits around a foot deep under the wind affected snow and wind slabs. This layer has been showing signs that it could still be reactive but is on a downward trend. The second layer down is the MLK Jr buried surface hoar. This layer is showing signs of only being reactive in the Summit Lake zone. Also in the Summit Lake region is weak snow near the ground. 

If you are headed out today watch for:
    -  Wind slabs on steep slopes. Rocky terrain with unsupported slopes (i.e. steep slopes with a cliff underneath) are the most suspect for popping out a wind slab that may be sitting on weak snow.
    -  Larger and more dangerous avalanches are possible in the Summit Lake and Johnson/Bench peak area where a thinner snowpack exists.
    -  SUN EFFECT and moist/wet sluffs on steep rocky southerly terrain. 
    -  Cornices. Warmer high elevation temperatures can help loosen these monsters and with good days and ridgeline travel, don't forget to give cornices a wide berth.
    -  Keeping with safe travel protocol such as exposing one person at a time.

 

           

Make sure to check out Heather's write up from the natural avalanche cycle on Fresno in the Summit area on 2/21. This event highlights the importance of matching avalanche terrain to the potential size of an avalanche. In this case, a portion of the fast moving debris overshot the main avalanche path and pushed up and over a subridge of hemlocks. 

 

For the snow geeks out there, a persistent weak layer round-up:

  • Valentine's Layer:  Small faceted grains, 10"-16" deep, last avalanches seen on this layer 2/21. Layer responsible for the 2/19 snowboarder remotely triggered slab on Seattle Ridge.
  • MLK Jr Layer:  Buried surface hoar, 2-3' deep, last avalanches seen in this layer 2/21 in the Summit Lake region.
  • Basal facets (large faceted snow near the ground): This layer has only been found in the Summit Lake region and produced at least one very large avalanche on Thursday, 2/21.

 

 

Turnagain Pass's beloved Tincan ridge yesterday, Saturday.

 


Additional Concern

Glide Avalanches

New glide cracks are opening up around our region and some are filled in and apparently not opening up. The last known glide release was on the south side of Goat mountain in Girdwood Valley on Tuesday 2/19. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks. A short list of known cracks in popular zones:  Magnum, Lipps, Seattle Ridge, Eddies, Lynx Ck. 


Small older wind slab on the lower SW shoulder of Lipps. Also, an old filled in glide crack is not easily seen, but the 'crumpled' up snow in the middle/lower portion of main slope is discernible. 

 


Mountain Weather

Yesterday:  Sunny skies prevailed region-wide. Ridgetop winds were light from a generally westerly direction. Temperatures hit 30F at many lower elevations with ridgelines in the 20'sF. A strong inversion has set up again overnight with cold air pooling in valley bottoms and at sea level. This morning temperatures at the mid and upper elevations are in the mid 20'sF while valley bottoms and sea level temperatures are in the single digits. 

Today:  Other than a possibility for some valley fog, today will be a carbon copy of yesterday. Sunny skies, light winds from the west and temperatures in the 25-30F range above the cold air trapped in valley bottoms. The cold air should mix out again in the afternoon warming parking lots and lower elevations to near 30F. 

Tomorrow:  The ridge of high pressure over the region looks to remain in place through the work week and possibly into the weekend. Sunny skies, some chance for valley fog, cold temperatures in low-lying areas and warm temperatures at the higher elevations are to be expected. Don't forget your sunglasses!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 25  61 
Summit Lake (1400') 15   0 30 
Alyeska Mid (1700') 24  57 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23 
Seattle Ridge(2400') 27  Variable 

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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