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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Thursday, February 14th 2013
Created: Feb 14th 6:57 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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Special Announcement

Stop by the motorized lot this Friday at 11AM! Join CNFAIC forecasters and Gold Level sponsor AMDS for an avalanche awareness event and memorial snowmachine ride on the 5th anniversary of this fatal avalanche in Turnagain pass. 

http://www.cnfaic.org/accidents/avy021508.htm


The Bottom Line

New snow and wind overnight, with more on the way today, will ratchet our avalanche danger to CONSIDERABLE above treeline and MODERATE below treeline. By this afternoon, we should see 12-20” of new snow accompanied by strong easterly winds at the upper elevations. All types of storm snow avalanches are out there today:  Wind slabs in all areas with recent wind deposited snow, storm slabs in areas out of the wind and loose snow sluffing. There is also a potential for avalanches to break 1-3’ deep in the existing pack, making for a larger and more dangerous slide.

Expert level route finding skills and keeping slope angles below 35 degrees is recommended - this includes slopes above or adjacent to you.


Primary Concern

Today will be one of those classic storm days - maybe not in the gnarly Chugach storm category, but it definitely has enough punch to spice up the avalanche conditions. We have had 6" of new snow at treeline overnight, which often translates to 8-10” at the upper elevations. With the addition of the same today, we are looking at between 1 and 2 feet of new snow in just under 24 hours. This is all being blown around by quite strong easterly winds (averaging 40mph, gusting 70mph). That said, it’s a text book case for storm snow avalanches:

Wind SlabWinds will be moving the snow around and loading slopes during the day. These slabs will be in the 1-4’ range and naturals are possible. Though wind slabs formed yesterday were quite stubborn due to the mild temperatures, don’t count on that today. Despite the mild temps, things are loading quickly and could be quite touchy regardless.

Storm Slab:  The new snow looks to be coming in slightly upside down. This can create a slab/weak layer combo in the storm snow and produce slab avalanches even out of the wind. This may or may not be an issue today, but it’s good to keep in mind.

Loose snowSluffing in the new snow should be prevalent and easy to initiate by a person.

Cornices:  These continue to grow and calve with each storm in the past couple weeks of warmer temperatures.

Below treeline:  Watch for winds that could possibly penetrate and load rollovers below treeline. Also, a series of crusts begin 6-12” below the existing loose snow.  This could act as a bed surface if enough weight overloads the snow at the top of the crust. Digging in with your hand and seeing how well the snow is sticking to the crust is always a good idea.


Secondary Concern

For the past few days we have been talking about a couple mid-pack crusts (1.5-3’ deep) and the weak snow that surrounds them. There are two in particular, one formed January 21-23 and the other January 30. These exist up to ~2,800’ - give or take depending on location. This facet/crust "sandwich" is disconcerting and has shown its head in the Girdwood Valley with a very large class 3 avalanche triggered Monday 2/11 in the Winner Creek area. We have been following these layers in the Turnagain zone since they were buried and they have shown little evidence to be a problem (no avalache activity/scary pit results) – yet…  This may be changing as we are now seeing some propagation propensity as Fitz found yesterday. In the pits my party dug, one out of three was concerning.

With today's rapid loading, we could possibly see avalanches break to these weak layers and bed surfaces. We could also potentially see new snow avalanches step down and trigger them. Today could be a good test.


Mountain Weather

Yesterday’s mild and overcast weather turned a bit obscured, windy and snowy as a quick hitting system moved through last night. Since yesterday afternoon we have picked up 6” of snow on Turnagain Pass and similar amounts in the Girdwood Valley. Summit Lake squeaked out a mere inch or two – but more is on the way! East winds have been strong, averaging 30-40mph with gusts over 70mph since 4pm yesterday. Temperatures have climbed a degree or two since midnight to 30F at 2,000’ and the low 20’s ~3,500’.

Another low pressure system is moving in currently, right on the heels of last night’s event, and should add an additional 6" at treeline. This will bump the strong east winds up even higher today with expected averages ~40mph and gusts to over 70mph. Temperature should hover around 30F at 1,000’ and the low 20’s on the ridgetops. The rain/snow line is expected to remain around sea level to 300’.

Tomorrow this system slowly moves out. Instability showers may add another few inches of colder snow as winds shift to a more SW direction. Saturday looks as though skies could break to some degree as we should be between storms.

 


 

Fitz will issue the next advisory tomorrow morning, February 15th.

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

Subscribe to the Turnagain Area Avalanche Advisory:

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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If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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