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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   John Fitzgerald  
Friday, December 19th 2014
Created: Dec 19th 6:55 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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'
 Show the Complete North American Avalanche Danger Scale
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The Bottom Line

The avalanche danger continues to be CONSIDERABLE in the alpine today.  Dense slabs up to 3' in depth could be triggered by skiers and riders between 2,500-4,000’ in elevation.  Avoidance of terrain over 35 degrees and trigger points such as steep rollovers and areas with thin snow coverage will be critical today.

In the treeline elevations, between 1,000-2,500’, the danger is MODERATE.  Slabs up to 2’ in depth could be triggered in steep terrain and areas where the overall snowpack is more shallow.  Avalanches initiated in the higher elevations have the potential to run down into this elevation band today.

Below treeline zero to a few inches of snow sit on the ground.  Rocks, stumps and open water are the main issues you will encounter at this elevation.

Yesterday a skier triggered an avalanche on the Southwest face of Sunburst.  The skier was caught, carried and fully buried.  Fortunately the skier and his partner were able to dig him out and walk away without injury.  Similar avalanches are possible today as a layer of buried surface hoar sitting under 2-3’ deep slabs holds the potential to propagate across large areas.

Sunburst skier triggered 12-18-14

click HERE, HERE and HERE for more detailed info on this incident.  Stay tuned for a more thorough write up on this incident.


Primary Concern

Our main avalanche concern today is one that will not go away quickly.  Surface hoar that formed a week ago has been preserved and is sitting below 1-3’ slabs.  Typically surface hoar gets knocked over and blown around before a slab builds on top of it.  That is not the case with our current snowpack.  The snowfall that began on December 13th came in with very little wind and allowed this layer to be buried intact.  We have been investigating this layer over the last several days and we have found it in all pits above 2,700’.

The tricky part with this set up now is that it is gradually becoming more difficult to trigger an avalanche.  We know this based on our test results in snow pits.  Unfortunately, it will be possible to test this layer by traveling in steeper terrain and not get results (NOT RECOMMENDED!)  Exceptions to this were found on Sunburst and in the Summit Lake region, where skiers remotely triggered an avalanche from 50’ away.  In areas such as this where the snowpack is thinner, it will be easier to initiate an avalanche today.

The nature of buried surface hoar is such that it persists as a weak layer in the snowpack for many days, sometimes weeks after it becomes buried.  Because of this we will be tip toeing around the mountains for the foreseeable future.

In order to stay out of trouble it is best to avoid steep terrain.  Terrain on all aspects over 35 degrees should be treated as suspect.  Avalanches, if initiated have the very real potential of propagating across large areas, making escape difficult at best.  There is plenty of evidence to support this and the problem will potentially take a long time to go away.  

Below 2,500’ in elevation the likelihood of triggering a slab avalanche 1-2’ in depth will be less than in the higher elevations.  A crust that has formed in the middle of this newest slab will make it harder to trigger any buried surface hoar that survived the rain and wet snow.  We cannot rule out the potential for triggering slabs in this elevation band and it will be important to keep slope angles low until we see more signs of this layer becoming non-reactive. 

Paying attention to what is above you, including other groups, when in this elevation band (bewteen 1,500-2,500') will be important as avalanches initiated in the higher elevations could run into the mid elevations today.


Mountain Weather

In the past 24 hours the precipitation has shut off and the temperatures have cooled - see table below.  Winds have picked up slightly overnight along ridge tops and are averaging in the 20mph range out of the East at Sunburst this morning.

Today expect light snow showers with 2” accumulation possible.  Temperatures at 1,000’ will be in the high 20s to low 30s F range.  Winds will be out of the Northeast at 10-20 mph.

The extended outlook is showing some potential for more precipitation as a complex series of Lows move through the Gulf and along the Aleutian chain over the next several days.  There is a high level of uncertainty as to the timing and track of these systems with the next best chance for snow coming Sunday into the early part of next week.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  28  0 0  28
Summit Lake (1400')  24  0  0  4
Alyeska Mid (1700')  27  0  0  18.5

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  25  ENE  11 42
Seattle Ridge(2400')  22 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: Dec 08, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedRain and snow have fallen in Turnagain Pass this week, but not enough to open for snowmachining. Continue to check back to this site for updates.
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail is expected to open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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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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