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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, April 4th 2018 4:44 am by Aleph Johnston-Bloom
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

With snow and wind in the forecast today expect the avalanche danger to rise from LOW this morning to CONSIDERABLE this afternoon as the storm intensifies. Storm slabs will grow in size and become more likely to trigger as the day progresses. Pay attention to changing conditions. In addition, keep in mind the chance of triggering an old hard slab avalanche 2-4' thick and give cornices a wide berth. 


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

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

How much snow will fall and how fast? Pay attention to changing conditions! Over a foot is forecast to fall along Turnagain Pass with the storm intensifying this afternoon. Snow in amounts in Portage may be closer to two feet. Snow today will be landing on a variety of surfaces ranging from wind hardened snow to melt-freeze crusts.  In some spots there are small weak facets resting on top of these hard layers. Will the new snow bond to the old snow? That really is the question of the day. As snow accumulates watch for cracking, listen and look for collapsing (whumpfing) and realize triggering a storm slab could become likely by this afternoon. Stronger winds will move snow around and help create deeper slabs in leeward terrain. 

Variable surface conditions that new snow may not bond well to. Photo: Troy Tempel

Soft facets over a hard crust. This could become a reactive set-up with new snow landing on top.

 

 


Avalanche Problem 2

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

With new snow in the forecast today is important to remember the current snowpack has a poor structure with many weak layers that sit 2-4' below the surface. Some times these layers can be woken up by additional load.  These layers are composed of facets and buried surface hoar. The slab on top is hard and varies in thickness due to prior wind effect. The snow surface has been beat up by wind and sun over the past three weeks. We are still concerned someone could find just the wrong spot on just the wrong slope and trigger a dangerous avalanche. Places most suspect are thin snowpack zones such as the Girdwood Valley and the South end of Turnagain Pass. Additionally, North and Easterly slopes in general have a thinner pack making them more suspect. Trigger points in this situation are often in thin areas near rocks or in scoured areas along ridges. 


Additional Concern

Cornice

Watch out for cornices along ridgelines. These could grow larger with new snow and wind loading today. As always, give cornices plenty of space and limit exposure underneath them. 


Mountain Weather

Yesterday was partly cloudy with temperatures in the teens to low 20Fs at upper elevations and the 30Fs around sea level. Winds were easterly 5-15 mph and picked up overnight with a few gusts into the 30s. 

Today will be mostly cloudy with skies becoming obscured. A storm is forecast to impact the advisory area with snow starting this morning.  Precipitiation intensity should ramp up this afternoon and continue overnight. There is a Special Weather Statement from the NWS. 6-10" of snow is forecast to fall today with another 10-15" tonight. Temperatures will be in the 20Fs.  Today and tonight winds will be Easterly 10-20 mph with gusts into the 30s and 40s.  

The storm should start to wind down by Thursday morning with skies becoming mostly clear by the evening. Friday into the weekend looks to be mostly sunny with a chance for snow again starting Monday. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  22  0  0  75
Summit Lake (1400')  21  0  0  31
Alyeska Mid (1700')  24  0  0  69

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  12  E  8  25
Seattle Ridge(2400')  18  ESE  15  34

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 06, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: ClosedClosed as of 4/27
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

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.


USFS SNOW AND AVALANCHE HOTLINE (907) 754-2369
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