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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   John Fitzgerald  
Saturday, March 21st 2015
Created: Mar 21st 6:34 am
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'
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The Bottom Line

The danger is MODERATE in the Alpine and upper end of Treeline elevations (>2,000').  Dense slabs up to 3’ thick could be triggered in steep terrain.  Sun and mild temps will increase the odds of triggering slabs as the day progresses.  Low to medium volume wet loose avalanches (natural and human triggered) will also be a concern on steep sunlit slopes.

The danger is LOW between 1,000’-2,000’, where a stout crust caps the surface and avalanches are unlikely.  The danger will increase slightly with daytime warming in this elevation band.


Primary Concern

Slabs between 2-3’ thick were deposited over the last week.  The bulk of that slab development happened 5 days ago.  Those slabs built on top of a wide variety of surfaces.  Our field day yesterday showed generally good bonding between these slabs and the underlying surfaces.  However, there is a high degree of variability in the makeup of these interfaces.  Many areas lack a persistent weak layer between the St Patty’s day slab and bed surfaces, but some areas have a thin layer of weak faceted snow.  It is in these areas harboring a thin layer of facets where you will be most likely to trigger a slab avalanche 2-3’ deep.  Last week we found this weak layer more widespread in the mid elevations and in sheltered areas in the Alpine.

Sounds tricky?  That’s because It is.  When the variability of the slab/weak layer interface is this high, it is challenging to accurately assess the stability of the snow below your feet.  Tracks on a slope are not a reliable indicator of stability when we have this set up.  The best ways to manage this problem are to dig in the snow and pick terrain that allows a margin of error should your assessment be off.  Avoiding steep sustained slopes that do not offer escape options will be important today.

Photo of a persistent slab that released yesterday in the afternoon on Tincan.  Trigger is uncertain, but is likely natural or remotely triggered by the party pictured at the top of the photo.

Tincan remote? 3/20/15


Secondary Concern

Another day of mild temperatures and occasionally intense sun will bring with it an increasing chance of triggering wet loose avalanches as the day progresses.  Expect wet loose avalanches to release naturally and be generally low in volume.  Human triggered wet loose avalanches could be larger.  For that reason it will be important to get off of steep sunlit terrain as the surface snow becomes damp.  The possibility also exists for the persistent slab problem (see above) to come in the form of a wet slab on steep sunlit terrain in isolated pockets, as pictured below.

Wet loosie triggers slab!


Additional Concern

Cornices have grown significantly this week.  As always it is important to steer away from cornices and know where the cornice begins and the terrain below you ends.  With the onset of Spring also comes long days with potentially intense sunshine.  Spikes in temperature as a result of sun and warm air can help to destabilize these behemoths.


Mountain Weather

Over the past 24 hours temperatures have been mild.  Winds have been generally light out of the East and no new precipitation fell.  Clear skies allowed the sun to impact solar aspects during the day and the surface snow to re freeze overnight.

Today expect mostly clear and mild conditions with high clouds streaming in from the East later in the day.  Winds will be light out of the Southeast at 5mph.  Temperatures at 1,000’ will reach into the mid to high 30s F.

We look to be in a generally mild and dry pattern through the weekend as weak Low pressure in the Gulf is held at bay by high pressure building over mainland Alaska.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 36 0 0 56
Summit Lake (1400') 31 0 0 12
Alyeska Mid (1700') 35 0 0 35

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 29 ENE 6 28
Seattle Ridge(2400') 30 n/a 6 16

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 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be 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.


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