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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, January 5th 2018 5:37 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 on all aspects and elevations above 2,000' where human triggered slab avalanches 1-3’ thick are likely today.  It may be possible to remote trigger an avalanche from above, below or adjacent to a steep slope. At elevations above 3,000’ triggering a very large slab avalanche that breaks in weak snow near the ground is also possible. Cautious route-finding and conservative decision-making are essential due to a complicated snowpack. 

Below 2,000’ the danger is MODERATE where an avalanche from above may send debris.


 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

Turnagain Pass is now open to motorized use. Special Avalanche Bulletin has been issued due to current avalanche danger combined with the anticipated snowmachine traffic. Human triggered avalanches are likely today on slopes steeper than 30 degrees in the alpine, above treeline and alder line. 


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Several weak layers are sitting under new snow from the New Years storm. Slab depths range from 15” - 30” with deeper amounts in the alpine, on the Northern end of Turnagain Pass, and in Girdwood. This poor set-up plus good visibility is the perfect recipe for human triggered avalanches today. Please understand there are several different dragons lurking in the snowpack right now. 1) a widespread layer of buried surface hoar that is showing signs of being reactive. 2.) weak facets near the ground in slide paths that released during the early December storm cycle, for example the SW face of Sunburst  3.) weak snow (basal facets) near the ground in the upper elevation (above 3,000’)

Rain fell during the end of the New Year's storm in the lower and mid elevation zones, which has now formed crusts in the top foot of the snow pack up to 2000’. Trigging an avalanche is more likely in upper portion of the Treeline zone where the snow quality quickly improves. Keep in mind today: 

  1. Human triggered avalanches 1-3’ thick are likely above 2,000'
  2. Several tracks may be on a slope before someone finds a trigger point and the whole slope release
  3. Remote triggering from the top, side or bottom of a slope is possible
  4. Avalanche size is expected to be large enough to bury and kill a person 
  5. The larger the slope the larger the avalanche

Additionaly, obvious signs of instability like “whumpfing” and shooting cracks may or may not be present. If winds increase above the forecasted 20mph, and you observe any blowing snow, this could form new wind slabs and add stress to the persistent slab problem.  

 

Two different people traveling near our pit location at 2750' experienced "whumpfing" due the buried surface hoar collapsing under the new snow. 


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Avalanche Problem 2

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

In the Alpine, above 3,000’, weak sugary snow (basal facets) sits near the ground. The storms over the past few days have added additional load to slopes that already have a hard slab, 3-5+ feet thick. In the upper elevations, a human triggered, large and dangerous deep slab avalanches is still possible. This is a high consequence avalanche problem that is impossible to outsmart and can take a long time to heal. Keep this in mind if clear skies allow for travel into the Alpine. It is really important to remember that triggering an avalanche in the upper layers of the snowpack may then initiate a deep slab avalanche. Cautious route-finding is essential. This includes thinking about the remote trigger potential from below. 


Mountain Weather

Yesterday skies were mostly cloudy in Turnagain Pass with clear skies in Girdwood. Temperatures along ridgetops were in the low 20’s (F) and upper teens yesterday and overnight. Temps at sea level were in the high 20F’s overnight. Winds were light and variable and no precipitation was recorded. 

Clear skies are expected today along with temperatures in the 20F’s at ridgtops and low 30F’s at sea level. Periods of valley fog are possible. Easterly ridge top winds could range from 5-20mph and no precipitation is expected.

Snow showers are possible this weekend, but not a lot of accumulation is expected. Temperatures could range from the low 20F’s at ridge tops to mid 30F’s at sea level. Easterly winds may bump up to moderate at times, 10-25mph on Saturday.

*Seattle Ridge anemometer is rimed. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 23  43 
Summit Lake (1400') 13  16 
Alyeska Mid (1700') 23   0 37 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 17  Variable  13 
Seattle Ridge(2400') 19  *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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