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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, December 26th 2017 4:20 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 and treeline elevation bands where triggering a hard wind slab will be possible on steep, unsupported slopes. Above 3,000’ triggering a much larger and more dangerous deep slab avalanche is also possible due to weak snow near the ground. 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. 

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

*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

Be suspect of unsupported slopes steeper than 30 degrees 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. Observations Sunday found hard supportable wind slabs as low as 1600’ on Eddies. These slabs averaged around 5” thick and were failing in hand pits on old weak snow. 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 that hard snow over weak 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. More on this below in the secondary concern. 

Cross loading on Seattle Ridge.

 


Avalanche Problem 2

Deep slab avalanches have been a concern in the advisory now for two weeks. We are not trying sound like a broken record but the message is the same. This set-up continues to warrant elevated caution and respectThis 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. 

Poor snowpack structure in the alpine, hard snow over weak snow near the ground. 

 Pastoral. Remotely triggered Deep Slab avalanche that occured on December 20th, 2017.

 


Mountain Weather

Yesterday was mostly cloudy with a few light snow showers and drizzle below 500'. The winds were light and easterly and temperatures were in the low 30Fs to mid 20Fs. Overnight skies cleared and temperatures dropped a bit into the the low 20Fs and teens. Winds shifted to the west and remained light.

Today will be mostly sunny with some patches of valley fog and temperatures in the low 30Fs to mid 20Fs. Winds will be northwesterly 5-15 mph. Tonight temperatures will drop down into the teens and skies will be partly cloudy. 

Wednesday is forecasted to be partly sunny with temperatures in the 20Fs and calm winds. Thursday looks to be pretty similar with some more sunshine on tap. Stay tuned for possible snow 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') *31  27 
Summit Lake (1400')  23 0 0  10
Alyeska Mid (1700')  29 0  29

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 21  ENE  22 
Seattle Ridge(2400')  25 SE   7 18 

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

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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
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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