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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Kevin Wright  
Saturday, March 15th 2014
Created: Mar 15th 6:42 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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Special Announcement

Placer river and Skookum are CLOSED to motorized use from the rain this week.  Seward district riding areas are OPEN.  Check the bottom of this page for the latest information on riding areas.


The Bottom Line

Since Monday Turnagain Pass has another ~50 inches of snow on the ground.  This has come through 2 storms – one that started Monday, the other that just tapered off late last night.   

This is a huge additional burden for the snowpack to hold.  The kicker is that this new snow is sitting on a persistent weak layer above the February melt/freeze crust.  Avalanche danger will be CONSIDERABLE at all elevations.

 Partly cloudy skies and a fresh blanket of snow will make for an enticing combination today.  This is not an "anything goes" kind of day.  Conservative terrain choices will be essential today.

 Avalanches may be difficult to trigger, but if you get something to move it’s going to be big and dangerous.


Primary Concern

It's been snowing - a lot!  Anchorage got a significant dump last night.  That snow extended to Girdwood and beyond.  This is the kind of maritime storm pattern that we are famous for, and we've been missing during this drought winter.  

The storm snow problem is least stable during the active part of the storm, and tends to stabilize quickly over time.  The big message today is that we got a LOT of snow and it will need time to settle out, bond, and stabilize.  We are still within the 24 hour window since active storming, and still within the window of high probability to trigger avalanches in the new storm layers.  

Storms also create wind slabs and build cornices.  Cornices are likely to be bigger and less stable than they were last weeekend.

Time will make these storm layers stable, but today is not the day to test them in big and dangerous terrain.  


Secondary Concern

Underneath all the fresh snow from the last 5 days is the prominent crust layer that formed in February.  Just above this crust is a weak layer of faceted snow mixed with buried surface hoar.  

We did some snow pit testing yesterday.  Results indicated the most concerning weak layer (above the Feb. crust) is difficult to initiate, but propagation potential is high.  The triggering is difficult because our slab layer (40-50 inches of new snow) is thick and strong.  This information tells us that avalanches may be difficult to trigger, but when they do the resulting avalanche can be large and deep.  

This kind of deep slab problem is most likely to be triggered from an area of shallower snow.  Wind loading patterns during the storm caused scoured ridges which quickly transition to deeply loaded slopes on the downwind side.  A skier or snowmachiner is more likely to trigger this problem near the scoured ridge than far into the deep pocket.  Once initiated, it could propagate across into the deeper snow.

Larger triggers are also more likely to initiate the deep slab.  Snowmachines have the disadvantage here with 600+ pounds of sled and rider weight impacting the slope.  


Mountain Weather

This has been a great week for snowfall.  Turnagain Pass more than doubled the total snow on the ground from 42 inches on Sunday to 88 inches last night.  Total new snow water equivalent is 5.9 inches.  Wind during the storm was predominately from the east on Sunburst.  Rain did reach up above 1000 feet at times during the storms, but the snow dried out at the tail end of the storm all the way to sea level.  

Last night we got a final shot of snow during a cooling temperature trend.  This last bit of the storm was widespread from Anchorage to eastern Turnagain Arm.  

A chance of snow continues today, with a couple more inches possible.  Decreasing clouds through the day may allow the sun to poke through at times.  Temperatures should be cooler, in the low 20s.  Wind will be light from the south.  

 

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