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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Kevin Wright  
Thursday, January 30th 2014
Created: Jan 30th 6:52 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.
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

Colder temperatures at all elevations are freezing the snowpack surface into a hard supportable crust.  The crust is adding a component to the snowpack that we haven't seen in a couple weeks - strength.  

Underneath the crust, especially below 3,000 feet and in areas where the total depth is shallow, there is still a lot of very weak moist snow.  We still must acknowledge the possibility of avalanches being triggered on these weak layers.  Just 2 days ago we saw explosives produce large avalanches.  

The danger rating is MODERATE for the possibility of human triggered slides that can break full depth.  Trigger points will be much more likely in shallow points on the snowpack.  The problem is affecting buried wet snow at low elevations and deep persistent weak layers at high elevations.  


Primary Concern

We don't have a lot of information about the high elevation deep slab because so few people have been traveling in the mountains over the last couple weeks.  Yesterday on Seattle ridge we dug in a deeper area at 2900 feet and found 5 feet of mostly very strong snow on top of the old Nov/Dec persistent weak layers.  (click on link for photos and pit profile)  We could not get an extended column test to fail, but 2 compression tests revealed sudden collapse Q1 failures at the early December drizzle crust (CT24, CT21 Q1).  The good news is that our recent wet storm has made some very strong snow - it's difficult to cut through it with a sharp saw.  I think it will be unlikely for a person to trigger the deep weak layers where the snowpack is in fact deep.  It may be possible to trigger from shallow points where it could propagate to much deeper snow.  


Secondary Concern

I'm still going to mention wet avalanches even though we now have a surface crust over everything.  You have to dig through the crust to find the wet snow.  

If someone were to trigger an avalanche below 3,000 feet, it will have some characteristics of a wet slab.  Think about heavy, slow moving, bulldozer-like avalanches.  

We dug a shallow pit just off the slope from the standard snowmachine up-track to Seattle ridge yesterday.  Underneath the 4 inch think supportable crust is unbelievable weak, moist snow.  Skis glide over the crust with no penetration, but trying to walk on it will sometimes punch a boot through the crust, which then drops through to the ground.  It's a very abnormal setup, and I'm honestly not sure how to measure its stability.  

As more of the snowpack freezes up with the colder temperatures, strength will increase quickly and the possibility of triggering more avalanches in the wet snow will decrease dramatically.


Mountain Weather

Sunny breaks over the last few days will continue today.  Southcentral Alaska is dominated by a blocking high pressure that is currently keeping clouds and storm from the west from entering our airspace.  The big weather change that is affecting our snowpack is a drop in temperature.  Ridgetop stations have been reading below freezing for over 48 hours.  Lower elevation sites are now also freezing up.  Wind is light and variable today.

Looking into the weekend - high pressure is expected to be the dominating feature for our region.  Mostly clear skies are forecasted, with valley fog in some areas.

Graphs show the temperature profile at Center Ridge (1880 ft) and Sunburst (3812 ft).  Blue line is 32 degrees (freezing).

 

 

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.


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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