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Avalanche Advisory

Turnagain Area Avalanche Advisory
Sunday, March 11th 2018 5:33 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

CONSIDERABLE avalanche danger remains at all elevations and on all aspects. Large slab avalanches 2-4' thick are likely to be triggered on slopes steeper than 30 degrees. These may be triggered from a distance or from the bottom of a slope. Cautious route finding and conservative decision-making will be essential for safe backcountry travel.

Summit Lake area - see Saturday's snowpack and avalanche summary.

*A Special Avalanche Bulletin has been issued through the National Weather Service. This will remain in effect through 6pm tonight. 


 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.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
Special Announcement

**Heightened avalanche conditions are being seen region-wide. Human triggered avalanche activity was reported in the South Fork of Eagle River yesterday

For the Hatcher Pass area, please see Saturday's HPAC avalanche forecast.


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering a large and unmanageable slab avalanche 2-4' thick remains our primary concern. Yesterday, a snowmachiner remotely triggered two slabs on Seattle Ridge from a meadow below the slope; it's important to remember that these avalanches can be triggered from the flats. These slabs were on the North end of the ridge above the powerline trail. This longtime Turnagain rider noted that avalanches in this area are not often seen. Additionally, similar slab avalanches were triggered in Girdwood Valley in the Notch Mtn area. 

The avalanche activity yesterday was all in the mid to lower elevation bands. Various layers of old faceted snow sit under the 2-4' of storm snow from Friday (photo of this below). The faceted layer has been overloaded by the new snow and is failing, creating the current 'persistent slab' avalanche problem. At the higher elevations, above 2,500', the facets are not as pronounced, yet there are old layers of buried surface hoar that are a concern. How likely a slab is to be triggered in these weak layers at the higher elevations is uncertain at this time. Of note is very little to no traffic was seen in the upper elevation bands yesterday. 

If you are headed out into the backcountry today things to keep in mind are:

  • The mountains are still adjusting to the several feet of new snow that fell two days ago
  • Watch and listen for whumpfing (collapsing) in the snowpack. This was noted by many folks yesterday, including the rider/skiers that triggered slabs. This means the snowpack is highly unstable and will almost certainly avalanche if the slope is steep enough.
  • Stick to slopes less than 30 degrees and ease into steeper terrain slowly - after careful snowpack assessment. Evaluate the consequences if the slope releases; where will the debris go?
  • If the visibility turns poor, be extra cautious to avoid being in a runout zone 

Slab avalanches on East faceing Seattle Ridge (looker's right of the up-track). Two of these could be the avalanches that were remote triggered from meadow below yesterday.


Loose snow sluffs on the West face of Magnum

 
Annotated photo of the storm slab bonding to the old snow surface, but the old snow surface is weak and failing. Hence, the new snow has 'overloaded' the older weak snow.


Three feet of new snow and wind effect on Tincan Ridge (left) and Seattle Ridge's Repeat Offender and uptrack zone (right). It's good to see the new snow, but slopes need time to adjust. 

  


Turnagain Pass flats - plenty of safe places to play that are out of avalanche terrain. (Photo: Allen Garrett) 

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Additional Concern

Cornice

Cornices have grown and are suspect for breaking while traveling along ridgelines. Give these an extra wide berth and minimize any time below them. Cornice falls can trigger avalanches on slopes below.


Mountain Weather

Yesterday cloudy skies with light snow showers gave way to breaking skies in the afternoon. Total 24-hour accumulation was 2-5" of low density snow in favored areas and no snow in others. Ridgetop winds were light to moderate from the East (5-20mph). Temperatures were in the mid 30'sF at sea level and in the teens along ridgetops.

For today, Sunday, a low pressure spinning East of us in the Gulf may push some moisture our way. Clear skies this morning are forecast to turn cloudy later today along with a chance that 1-3" of light snow will fall. Ridgetop winds look to shift to the North and West and stay light (5-10mph) as we are on the back side of the low pressure. Temperatures will remain cool for March, in the mid 30's again at sea level and teens along ridgetops. 

Looking ahead to the work week, Monday another system passes through with a chance for snow followed by clearing and the chance for a nice day on Tuesday. Unsettled weather looks to continue later in the week.


*Seattle Ridge anemometer (wind sensor) rimed over and not reporting

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 28  0.4  93 
Summit Lake (1400') 24  36 
Alyeska Mid (1700') 27  0.2  82 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 17  NE  14  38 
Seattle Ridge(2400') 23  *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, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: ClosedClosed as of 4/27
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

Subscribe to the Turnagain Area Avalanche Advisory:

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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