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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Thursday, February 19th 2015
Created: Feb 19th 6:17 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.
0 NO RATING Below Treeline / Below 1,000'
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The Bottom Line

The avalanche danger remains CONSIDERABLE at the higher elevations above 2,000' where very weak snow sits under a hard slab 1-3+' thick. Because of this poor snowpack structure, human triggered large slab avalanches 1-3' deep continue to be likely on steep slopes (> 35 degrees) and may pull back further than expected. Triggering an avalanche remotely, from a ridge or from below for example, is possible. Signs of instability such as collapsing/whoomphing may not be present until it's too late

The avalanche danger is MODERATE below 2,000' where the moist snowpack is re-freezing and the greatest hazard is an avalanche from above running into this zone.

*Sticking to lower angle terrain is again the best strategy for a safe day in the backcountry.


Primary Concern

The last two days have brought warm, sunny spring-like conditions to Turnagain Pass and today will be much the same. After several human triggered avalanches on Tuesday, there were no reported slides yesterday - however, very few people were out. Although the weather is inviting, the snowpack is not. A very poor structure exists currently and is one that will likely persist for the foreseeable future. The set-up is simple: a hard slab 1-3' thick over weak faceted (sugary) snow on top of a hard bed surface. This is textbook for human triggered slab avalanches. 

The slab on top of the weak layer is quite variable due to the strong winds during Monday's storm. There are portions of terrain that have been scoured to the point of uncovering old tracks (anti-tracks) and areas where a slab thickens from 0 to 30" over just 10'. These are extreme examples, but my point is - sussing out trigger points and how one triggers an avalanche today. Thin areas of the slab, roughly 1' or less, are the most likely places for a person to trigger an avalanche. The thicker areas of the slab will take a group of people near each other, such as a large party congregated on a ridgeline, something we call large triggers. Large triggers also include snowmachines - yet our unprecedented lack of snow has kept motorized use closed.

Not only is sussing out trigger points a hard thing to do and a bit too much to gamble on right now, but another thing to consider is the potential lack of obvious signs of instability. Collapsing or whoomphing was widespread two days ago, but less so yesterday. Don't let an absence of these signs lure you into thinking the snowpack is stable until it is too late. All you have to do is dig in a couple feet and you'll see for yourself the weak faceted snow that is plaguing the mountains. 

Photo and Video - Textbook slab avalanche ingredients:




Windloaded slopes vs. scoured slopes. Avoiding steep windloaded areas is a good strategy right now.


Mountain Weather

A nice day was had in the backcountry yesterday with mostly sunny skies and light Northerly ridgetop winds. Temperatures were in the low to mid 20's F on the ridgetops and in the low 30's at 1,000'.

Today looks to be similar - another warm spring like day - with clear skies and light variable ridgetops winds. Ridgetop temperatures should be in the low 20's F with valley bottoms in the low 30's F. 

Looking ahead to Friday through Sunday, another juicy North Pacific storm is on tap. Once again this low pressure will pump very warm air from the South along with the moisture. Models are showing a rain/snow line around 2,000-2,500' at this point with accumulated precipitation in the 1-1.5" range beginning Friday afternoon through Sunday.


*There is no wind information for both Sunburst and Seattle Ridge. The next closest stations near Turnagain Pass are Max's Mountain (Alyeska) and Penguin Peak (above Bird) and Fresno Ridge down near Summit Lake. We will be fixing these as soon as possible!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 29   0   0 43 
Summit Lake (1400') 24  0  0
Alyeska Mid (1700') 29   0 26 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  21 Wind  sensor destroyed 
Seattle Ridge(2400') 25  Wind   sensor is   rimed 

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: Nov 18, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedOnly a few inches of snow sits at the motorized lot, not enough to open for snowmachining at this time. Updated Nov. 18, 2017
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.


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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