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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, February 2nd 2018 5:01 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger is MODERATE above 2,500' for triggering a slab avalanche 1-3' thick. Slopes with signs of wind loading will be the most suspect for triggering an avalanche. Additionally, watch for easily initiated loose snow avalanches (sluffs) on steep slopes.

Below 2500' the danger is LOW.  Remember low danger doesn't mean no danger. 


 Show the Complete North American Avalanche Danger Scale
2 Moderate Alpine / Above 2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Roughly 1-3 feet of snow is covering a widespread layer of buried surface hoar across our region. In many places this snow is too loose to form a slab and the surface snow ’sluffs’ away with the weight of a person. In some areas of the alpine this week, where winds have created a denser more cohesive slab, the buried surface hoar has been reactive to both skiers and snowmachiners. Yesterday a group on Eddies triggered a slab remotely from the ridge above the steep Southwest face. This slab was 2 feet deep by 80 feet wide and ran to valley bottom. In general these slabs have been small in size, but large enough to take someone for an undesirable ride over rocks or possibly bury a person in a terrain trap. With that said a lot of people have been riding and skiing in steep terrain without incident where winds didn’t affect the snow or form a slab. In the periphery areas of Girdwood to Placer Valley where more sustained winds affected this zone, slabs may be larger and more connected. Basically this problem requires the ability to assess the snow and terrain as you venture into the mountains with an understanding that triggering even a small soft or hard slab could have consequences in the wrong place. Identify terrain traps like gullies, cliffs or rocks below before committing to a steep slope.  

Snowmachine triggered avalanche in God's Country near Pyramid on a SE aspect that was triggered remotely on Sunday.

 

 Natural slab avalanche on Wolverine's South face that occurred near the end of the storm last Friday. This is a good example of the potential size of a persistent slab and the kind of steep wind loaded terrain it could found in.

 

Hand pit on Sunburst at 3300' on West aspect revealed the very large and well preserved buried surface hoar that is suspect in places with a consolidated slab. 


Avalanche Problem 2

Dry Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Expect loose dry snow to be fast moving in steep terrain and entrain more snow as it picks up speed. This quick moving surface snow can knock a person off their feet. Be aware of the consequences below you and manage your ‘sluff’ by slowing down and letting it pass you. 

Sluffing around ski tracks on SW face of Sunburst


Additional Concern

Deep Persistent Slabs

Two and a half weeks have passed since a storm delivered heavy rain and strong wind to our region and caused a natural deep slab avalanche to release on the Southwest face of Sunburst. Immediately following this event the snowpack stabilized below 3000’ due to wet snow freezing into a solid strong layer. Observations over the last few weeks have found poor structure  (basal facets) near the ground in targeted thinner areas of the snowpack above 3000’. This leaves us with some degree of uncertainty in the upper most reaches of our forecast zone. Triggering a deep slab avalanche is becoming more unlikely with time, but is not impossible on a large steep slope combined with thin trigger spots to initiate such an avalanche. Should you find yourself approaching a 4000’ peak, remember this is a hard to trigger, low likelihood problem that deserves acknowledgment of it’s potential. 


Mountain Weather

Yesterday skies were clear and sunny with a temperature inversion, single digits (F) in valley bottoms and low teens (F) near ridge tops. Winds were light from the East in the morning becoming light and variable the rest of the day. No precipitation has occurred this week. 

Today looks similar with clear skies and an inversion causing temperatures in the single digits in valley bottoms. Temperatures may reach the low 20F’s in mid and upper elevations. Winds are expected to remain light and variable with no potential for precipitation today.  

A strong high pressure over mainland Alaska is expected to dominate our region through the weekend with continued clear skies and cold temperatures. Offshore winds may be present in Coastal areas and gap zones over the weekend. The first chance for this high pressure pattern to start shifting is Sunday into Monday, but confidence remains low at this point. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 14  64 
Summit Lake (1400') -1   0 17 
Alyeska Mid (1700') 10  51 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 11  Variable   20
Seattle Ridge(2400') 12  Variable   16 

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