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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Kevin Wright  
Friday, February 14th 2014
Created: Feb 14th 7:01 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.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
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The Bottom Line

A storm system is currently bringing snow to Eastern Turnagain Arm.  4 inches have accumulated by 6am, and another 5-9 inches are forecasted through the daylight hours today.  

Storm snow combined with wind and our old persistent slab problem may push us into CONSIDERABLE avalanche danger later today above treeline.  Below treeline is expected to stay LOW to MODERATE without wind loading.  

We can piece out the various avalanche problems today, but the overall concern is related to the snow since February 7th.  This snow is still soft, but rests on a very hard crust layer and may not be bonded well to the crust.  


Primary Concern

We continue to document loose and very weak facets between the January melt/freeze crust and the February 7th storm snow.  This layer was responsible for a number of small human triggered avalanches in the last week.  It continues to be the most likely culprit for significant avalanche activity today, especially when combined with new snow and wind.  Check out this observation for photos and snowpit data regarding the facet layer.  

Avalanches witnessed on this layer have thus far maintained a consistent pattern with relatively small size (12-20" deep), and lower volume.  Keep in mind that bigger and steeper terrain will produce larger and more dangerous avalanches.  With more snow and wind the depth of this slab layer will be reaching 24-30" in wind loaded areas.  

The 2 properties necessary to create this type of avalanche that are not always found -

1.  A cohesive slab - some wind loading and stiffening is necessary to create connectivity of the surface snow, otherwise it's just loose powder with sluff potential.

2.  A faceted interface between the new snow (Feb 7th storm) and the underlying crust (January melt/freeze).  In places where the facets are present, this is a significant weak layer consisting of loose sugary grains with poor bonding.  


Secondary Concern

Yesterday afternoon we witnessed a very small natural avalanche occur during a short spell of wind.  Our light dry snow on the ground is easily transported by wind and wind slab can build quickly with only moderate wind velocities.  Additional storm snow by itself is probably not enough to be a significant avalanche problem, but combined with wind it will produce pockets of unstable snow.  

Wind slab is expected to be isolated to higher elevations above treeline, and may not form if the wind stays light today.  


Mountain Weather

Just a couple inches of snow had fallen yesterday before we got a clear break and periodic wind activity.  Wind was reaching gusts to 52 mph and blowing snow around at ridgetop levels.  

The large low pressure system over Kodiak is sending our region waves of cold precipitation today.  As of this morning we have another 3-5 inches of snow on the ground and it is forecasted to continue through the end of Friday.  Wind has backed off a little.  Temperatures remain cold but are increasing slightly.  Currently Center Ridge snotel is reading 11.5 degrees.

Unsettled storm patterns will continue through the weekend, originating from the low pressure system in the northwest gulf.  We can expect more of the same weather for a few more days.

 

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.


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