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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, December 27th 2017 4:42 am by Aleph Johnston-Bloom
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, above 3,000’ where triggering a large and dangerous deep slab avalanche is possible due to weak snow near the ground. Additionally, in both the alpine and treeline elevation bands triggering a hard wind slab is still possible on leeward, steep, unsupported slopes. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully.

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

*Please remember your safe travel practices! This includes, exposing one person at a time in avalanche terrain, watching your partners, being rescue ready and having an escape route planned.


 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

If this is your first day reading the advisory this winter it is important to know that deep slab avalanches have been a concern in the advisory now for two weeks. If you have been following along all season we are not trying sound like a broken record but the message is the same. This snow pack set-up continues to warrant elevated caution and respect. It is a high consequence avalanche problem that is impossible to outsmart. The snowpack 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 facets. Observations over the last few weeks indicate this poor structure is widespread across our region in the alpine elevations.  

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

  • Large snow covered slopes that do not have piles of old debris under them are all suspect 
  • Thinner areas of the snowpack (1-2’ thick) are likely trigger spots as well as scoured areas near rocks 
  • It is possible to trigger this avalanche from below and it could run further than expected. Choose terrain wisely!
  • 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

Obvious clues like ‘whumpfing’ and shooting cracks may not be present until it is too late. Evaluate snow and terrain very carefully and steer clear of large loaded slopes.

Pastoral avalanche that occurred on December 20th and was remotely triggered. Photo: Trip Kinney

  


Avalanche Problem 2

Be suspect of steep unsupported slopes that have a fat, smooth, pillow-type shape to them. Strong Easterly winds over the weekend changed the surface conditions of our forecast zone, creating hard wind slabs on leeward features. The wind slabs may be farther down slope due to the high wind speeds or only found on one side of gully features due to cross loading.  Any wind slabs today will be hard and supportable (to a skiers weight), they could be stubborn to initiate and may lure a skier well onto a slope before it fails. Listen for that hollow, drum-like sound below your skis or use a pole to probe for a hard snow over weak snow set up.  These slabs could be as thick as 1-2’ deep in upper elevations and if triggered in the alpine have the potential to initiate a much larger and more dangerous deep slab avalanche.

Natural wind slabs on Seattle Ridge that happened sometime during the wind event just prior to Christmas. 

 


Mountain Weather

Yesterday was mostly clear and sunny with valley fog. There was a temperature inversion. Temperatures were in the low 20Fs to teens at upper elevations and teens in the valleys. Overnight temperatures dropped down into the single digits in the valleys. Winds were light and variable.

Today will be similar with valley fog and sunshine above. Temperatures will be in the low to mid 20Fs and winds will be light and variable. Temperatures will be in the teens overnight and winds will remain light. 

Tomorrow also looks like it will be mostly sunny becoming cloudy overnight into Friday.  There is a chance of snow showers over the weekend.  

 

*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') *23  29 
Summit Lake (1400')  7  11
Alyeska Mid (1700')  18 26 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  17  W 13 
Seattle Ridge(2400')  18  Varible  3  6

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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