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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   John Fitzgerald  
Monday, February 18th 2013
Created: Feb 18th 5:45 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.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
 Show the Complete North American Avalanche Danger Scale
The Bottom Line

The avalanche hazard is MODERATE today above treeline where loose snow avalanches and older isolated pockets of wind slab will be the main concerns.  The mid elevations, between ~1,500-2,800' continue to have a MODERATE hazard where a weak layer sits on a crust buried 2-3' deep.  The avalanche hazard is LOW below treeline today, where recent snow has adhered well to older snow surfaces and avalanches are unlikely.


Primary Concern

Loose Snow Avalanches

New snow in the past 24 hours fell in many places without any associated winds.  Up to a foot of new snow can be found in the upper elevations with half that amount in the lower elevations.  This snow is "right side up", as temperatures overnight have gradually cooled.  Loose snow avalanches will be a concern on steep upper elevation slopes today.  Periods of sunshine will increase the likelihood of triggering these slides.  These avalanches have the potential to knock people off of their feet or snowmachines.  As such it will be best to avoid steep slopes above terrain traps where sloughing could pull people into gullies, over cliff bands and into trees.

Wind Slabs
In the upper elevations isolated pockets of older wind slab may be triggered by a skier or rider today.  These pockets will be harder to detect, as a blanket of lighter density new snow sits on top of these slabs.  Staying off of steep previously wind loaded terrain features will help in avoiding this problem today.
With light to moderate winds forecasted for today, expect to see shallow new wind slabs forming near ridgetops through the day. With ample light density snow available for transport, expect these slabs to form easily and be most sensitive as they are forming.


Secondary Concern

The mid elevations (between 1,500-2,800') have a snowpack structure that has some potential to produce larger more dangerous avalanches.  A crust formed in late January has a very thin layer of weak snow above it in many areas.  Above that weak layer are slabs ranging in depth from 1-3 feet.  We have been investigating the likelihood of triggering an avalanche on this interface and have found mixed results within our forecast zone.  In some areas snowpit tests have shown this layer to be reactive and in other areas it has been a non issue.  While we've only had one report of a human triggered avalanche on this layer in the last week, the potential still exists.  The best way to avoid this problem is by managing your terrain and staying away from potential trigger points (e.g., steep rollovers, areas of thin snow) within this elevation band.


Mountain Weather

Snowfall that began in the early morning hours on Sunday have accumulated up to a foot of new snow in the higher elevations.  Water amounts across the area range from .75" in the Girdwood Valley, .5" on Turnagain Pass and .3" at Summit Lake.  Winds have been very calm out of the North.  Temperatures have been on a steady decline this morning with ridgetop stations reporting an average of 10 degrees F.

Today we should expect to see snow showers tapering off in the morning giving way to clear skies by this afternoon as a brief pause between storms takes hold.  This break will be short lived, as the next low pressure system moves into the area from the Southwest by tomorrow afternoon.

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Wendy will issue the next advisory tomorrow morning, February 19th.

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: Mar 15, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: Open
Skookum Drainage: OpenSkookum drainage closes to motorized use on April 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: Open
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: Open
South Fork Snow River Corridor: Open
Summit Lake: Open

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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
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