Avalanche Advisory

Turnagain Area Avalanche Advisory
Saturday, April 18th 2015 6:33 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

There is a HIGH avalanche danger in the backcountry where heavy snowfall, rain and gale force winds are rapidly loading an already unstable snowpack. Large avalanches are likely to occur naturally and human triggered avalanches are very likely on all aspects and at elevations above 1,000'. These slides can be up to 5' deep, or more, and could propagate across entire slopes; nothing to mess with.

*Hiking trails with avalanche paths above, such as the Crow Pass and Portage Valley areas, should be avoided as debris can funnel into snow free zones and cover portions of trail.

Today's message is simple: Travel in avalanche terrain is not recommended, period. This includes runout zones and valley bottoms where debris from an avalanche releasing above can run. It's a good day to curl up and watch a movie or finally finish your taxes if you filed an extension...

 Show the Complete North American Avalanche Danger Scale
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.
Avalanche Problem 1

It was an exciting day in the mountians yesterday with a very touchy snowpack in the elevation band between 2,000 and 3,000'. There were three known large avalanches that occurred (3-5' deep). Two were triggered at the same time, but on different aspects, from the corniced ridgeline on Tincan (CFR ridge) and one was a natural avalanche on Magnum's North face near Taylor Pass. You can see many great photos and some write ups on our observation page HERE.

Deep Persistent Slabs:
The primary concern for today are naturally occurring deep slab avalanches that fail in lower layers of the snowpack. These can be up to 5' thick or more and propagate across entire slopes and terrain features. With a foot of new snow and strong wind overnight adding load to an already unstable snowpack, it's a simple equation to stay away from avalanche terrain. 

There is a mixed bag of weak layers, crusts and interfaces buried anywhere from 2-4+' deep in our current snowpack. We are unsure what layer was responsible for yesterday's slides, but the take home point is: There are weak layers/interfaces that have been slowly loaded during the past 2 weeks of storms which are, clearly, still showing signs of reactivity. 

Photos below are of the large slab avalanche on Tincan's CFR bowl, Southwest facing (left photo: Adam Phillips, right photo: Barkley Blair).



Images below are of the skier triggered slides off both the North and South side of Tincan's CFR ridgeline. To have deep slab avalanches release on two opposite aspects is very unusual and speaks to our currently very complicated snowpack.

Avalanche Problem 2

Storm snow avalanches associated with just the new snow will be likely but not as large as the deep slab issue mentioned above. Today we can expect wind slabs and storm slabs 1-3' thick, depending on how much new snow falls. Sluffs should also be expected and could trigger a slab lower on the slope. Cornices will continue to grow and have the ability to fall and trigger large avalanches as well.

Wet Snow Avalanches:
We can also expect wet slab avalanches in the lower elevation band between 1,500' and 2,500' due to rising temperatures and a rising rain/snow line today and this afternoon.

Mountain Weather

Partly cloudy skies yesterday morning quickly gave way to wind and light snowfall by the early afternoon. Heavy snow began falling overnight along with strong Easterly ridgetop winds. There has been around a foot of new snow at Turnagain Pass and Girdwood Valley with a rain/snow line ~500. Winds have been wreaking havoc at hourly averages in the 60's and gusts to 107mph. See the charts below for additional 24-hour data.

Today we can expect a short break in precipitation before another 10-14" of new snow is forecast to fall later today (~1" water equivalent) with a rain/snow line rising to possibly 1,500', and even higher. The gale force ridgetop winds are expected to continue from the East, averaging in the 50-60mph range. Temperatures look to rise to the upper 20's and possibly 30F on the ridgelines and the upper 30's at 1.000'.

The pulse of precipitation that moves in later today should remain through tomorrow with periods of heavy snowfall and rain to 1,500'. Monday we could see a break in weather before another round of rain, snow and wind early this coming week.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 33  11  1.1  84 
Summit Lake (1400') 35  0.2  14 
Alyeska Mid (1700') 32  12 0.95  50 


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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 22  ENE   38  107 
Seattle Ridge(2400') 25  n/a   40 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: Mar 15, 2018 )

Glacier District
Johnson Pass: Open
Placer River: OpenPlease avoid private property and AKRR job site at Luebner Lake. Cross railroad tracks if needed, do not ride down tracks, it is illegal.
Skookum Drainage: OpenCross railroad tracks if needed, do not ride down tracks, it is illegal. FYI, Skookum drainage closes to Snowmachines on 4/1 as per the Chugach NF plan.
Turnagain Pass: Open
Twentymile: OpenCross railroad tracks at designated spot as you leave the parking area.
Seward District
Carter Lake: Open
Lost Lake Trail: Open
Primrose Trail: Open
Resurrection Pass Trail: OpenResurrection Pass trail is open to snowmachine use during the 2017/18 winter season.
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.

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