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Avalanche Advisory

Turnagain Area Avalanche Advisory
Sunday, December 24th 2017 5:27 am by Graham Predeger
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

There is a MODERATE avalanche danger today in the alpine and treeline elevation bands where triggering a hard wind slab will be possible on steep, unsupported slopes.  Above 3,000’ deep slab avalanches are still a possibility given the poor structure that we know exists high in the alpine.  If you decide to venture out, cautious route finding and conservative decision-making will be key today given our current avalanche concerns.

There is no hazard rating below 1,000’ due to a lack of snow. 

**Click HERE for the Summit Lake Summary posted yesterday.


 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.
0 NO RATING Below Treeline / Below 1,000'
Avalanche Problem 1

WIND was the word yesterday.  Moderate to strong easterly winds are wrecking havoc in the upper elevations thru Turnagain Pass.  Even mid- slope yesterday, easterly winds were actively transporting any loose surface snow available and building hard wind slabs in leeward terrain, leaving only scoured ridges and anti-tracks in its wake.  Any wind slabs today will be hard and supportable (to a skiers weight) and may lure a skier well onto a slope before it fails.  Be suspect of unsupported slopes steeper than 30 degrees that have a fat, smooth, pillow-type shape to them.  Listen for that hollow, drum-like sound below your skis or use a pole to probe for that hard snow over weak set up.  Triggering even a small wind slab could have very high consequences especially in the upper elevations where there is also a potential for initiating a much larger and more dangerous deep slab avalanche. More on deep slabs below. 

 

Impressive wind transport in the alpine looking South across Turnagain Arm from the Forest Service office in Girdwood.

 

Anti-tracks and a variable surface of mostly hard, wind-affected snow left in Common bowl, Tincan.  

 


Avalanche Problem 2

The recipe for deep slab avalanches has been found in the upper elevations of our forecast zone, above 3000’ on slopes that did not avalanche during the early December storm cycle. The snowpack ranges from 3-5+’ thick and is sitting on weak basal facetsObservations over the last few weeks indicate this poor structure is widespread across our region in the alpine elevations. This is a high consequence avalanche problem that is impossible to outsmart.

 

 

 

When dealing with a deep slab avalanche problem, keep in mind:

  • Thinner areas of the snowpack (1-2’ thick) are likely trigger spots as well as scoured areas near rocks   
  • Due to strong winds over the last month the snow depths are highly variable and there may be more trigger spots than we realize
  • Thicker areas (3-5+’ thick) will be difficult to trigger and several tracks may be on a slope before someone finds a trigger point
  • It is possible to trigger this avalanche from below and it could run further than expected 
  • Large snow covered slopes that do not have piles of old debris under them are all suspect 

 

On Wednesday December 20th, two skiers approaching Pastoral Peak remotely triggered this very large avalanche from below. Luckily they were able to run from its path and avoid being caught. This is a very scary set-up that is likely not going away soon.  More info on this avalanche here.


Mountain Weather

Clear skies and strong Easterly winds dominated our region yesterday.  Generally ridge top winds were in the 20-30mph range and gusting into the 40s during the daylight hours.  Winds peaked late last night with Sunburst seeing a gust to 93mph at midnight.  Pockets of warm air in the Valleys were stubborn to erode with temps in Girdwood and Portage in the 40’s F thru much of the day.  Ridge top temps were in the mid to high 20’s F.

Today we can expect to see 1- 3” of snow as a weak front moves north across the Kenai Peninsula.  Temperatures are expected to drop with the approach of the front and should promote snow in most areas.  Ridge top winds will be in the 10-30mph range from the East. Daytime temperatures at 1,000’ are expected to be in the low 30’s F and dipping into the 20’s overnight.

Whatever precip we can squeeze out between now and the end of Christmas Day may be it for a few days as another high pressure looks to be setting up as we head back in to the work week.

**Center Ridge SNOTEL is reporting erroneous temperature data. See Turnagain Pass DOT weather station for accurate temperature at 1000'

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  **27   0   0    31 
Summit Lake (1400') 29    0  0  11
Alyeska Mid (1700')  32   0  0   26 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  24 ENE   42 93 
Seattle Ridge(2400') 28  ESE  26  70 

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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