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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Saturday, December 19th 2015
Created: Dec 19th 5:56 am
4 High Alpine / Above 2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
4 High Treeline / 1,000'-2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
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.
 Show the Complete North American Avalanche Danger Scale
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Special Announcement

Don't forget to come by the motorized lot at Turnagain Pass tomorrow for a Free Avalanche Rescue Workshop!!. This event is hosted by the CNFAIC forecasters and is a great opportunity to practice beacon searches, learn strategic shoveling techniques. This workshop is open to everyone and anyone, novices and experts.


The Bottom Line

The avalanche danger will be rising to HIGH today in response to heavy snowfall combined with strong winds in the Turnagain Pass and Girdwood Valley areas. Avalanches occurring naturally are expected at elevations above 1,000' where new snow and winds are loading the steeper slopes. Human triggered avalanches in these areas are very likely. As the storm continues, traveling in avalanche terrain is not recommended. A MODERATE danger exists below 1,000' where an avalanche occurring above may run into this zone.

*If you are thinking of heading into the backcountry today, terrain management will be the key in order to stick to mellow slopes and avoid slopes 35 degrees and steeper. This includes runout areas; for instance the bottom of the gullies along the front side of Seattle Ridge. Once the snowfall stops and skies break up, very careful snowpack evaluation is necessary and a conservative approach is needed before deciding to enter slopes 35 degrees and steeper. 


Primary Concern

A moisture laden storm is currently moving through the Gulf bringing heavy snowfall to elevations above ~800' and rain below in the Girdwood Valley and Turnagain Pass zones. Winds have been strong with the snowfall from the East - 30-40mph with gusts in the 70's mph. Snow totals at the mid-elevations from overnight are:

Girdwood Valley:  8-10+"
Turnagain Pass:  9-11+"
Summit Lake:  2-3"

We are expecting an additional 10-15" to fall today before the storm slows down tonight. A variety of storm snow avalanches are expected today. These include:

WIND SLABS:  With such strong winds associated with the snowfall, much of the avalanche activity is likely to be on wind loaded slopes. These 'wind slabs' are expected to be 1-3' thick and standard storm-induced slabs that are the most unstable during wind loading and directly after, but can stability quickly.
STORM SLABS:  In areas sheltered from the wind we may see slabs release from denser storm snow falling over less-dense snow.
LOOSE SNOW:  Loose snow avalanches are likely on very steep and rocky terrain.

*In addition to the avalanches expected within the storm snow, there is a possibility that a slide could break into weaker layers that reside 2-3' deep in the pack. If this is the case, then large avalanches could result. More on this below.

Photo: The approach of the storm. This photo was taken yesterday afternoon by Andy Moderow. A soft, but wind affected, pre-existing surface is now covered with 8-10" of new snow from overnight with another 10"+ today. The good news is, there are no weak layers on yesterday's surface and bonding with this new load should occur relatively quickly (in a day or so after the storm).

 


Additional Concern

Around 2-3' below the snow's surface sits a layer of weak snow on top of either a hard crust (elevations below 3,000') or a hard old wind surface (above 3,000'). The weak snow is comprised of facets that are bonding and in some cases surface hoar. In all our pit tests these weak layers are proving to be quite strong and unreactive. However, with a good shock to they system today - around 2" of water weight rapidly added to the pack - we can't rule out the potential that these old weak layers may become overloaded and a large avalanche release.


Mountain Weather

We saw a brief break between storms yesterday as skies broke up and snowfall ceased for the middle part of the day. The Easterly winds, on the other hand, remained strong enough that several folks noted plumes on the peaks during the day. 

Overnight, a Pacific storm moved in and has, as of 6am this morning, added up to a foot of new snow at the higher elevations (above the snow stations). See tables below for snowfall and water numbers at the stations. The rain/snow line is hovering right around 800' currently and expected to remain. Ridgetop winds picked up as well overnight into the 30-40 mph range with gusts in the 70's. For today, we should see this very stormy weather continue though this evening before the storm starts thinking about moving out.

Tomorrow, we should see instability showers with moderate Easterly ridgetop winds. This means we could see either skies open up a bit or light snow showers. Stay tuned.

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 29  0.7  55 
Summit Lake (1400') 26  0.2  19 
Alyeska Mid (1700') 31  0.66  39 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  NE  20  77 
Seattle Ridge(2400') 25  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: 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.


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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