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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, February 6th 2018 4:45 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

The avalanche danger is MODERATE above 2,500' for triggering a wind slab up to a foot thick. Keep mind the overnight wind loading may have also added stress to older persistent slabs that could break deeper in the snowpack. Additionally, watch for cornices along ridgelines and sluffs in steep terrain.

*For the periphery zones, such as Girdwood to Portage Valley, and Johnson Pass to Summit Lake, more caution is advised where a slab could be larger and more connected.

Check out the Summit Lake Summary HERE.

 


 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.
Special Announcement

For all the Hatcher Pass users out there - Hatcher Pass Avalanche Center is having their annual fundraiser this Saturday night, Feb 10th at the Palmer Moose Lodge!! HPAC is a growing avalanche center for a high use zone with a high number of avalanche accidents in Alaska, they need your support! Click HERE for details.


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

After a week and a half of sunshine and cold temperatures the clouds rolled in, temperatures rose and the winds picked up. Seattle Ridge recorded easterly winds in the 20s and gusting into the 40s starting at 3pm yesterday and continuing through the night. Although we only received an inch of snow overnight at Turnagain Pass and none in Girdwood there is enough old soft snow to blow around. Look for newly formed wind slabs in leeward terrain. Pay attention to slopes where the snow feels stiff, looks pillowed or sounds hollow and watch for shooting cracks. A small slab in the wrong terrain could have high consequences. 


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

The wind overnight may have also stiffened existing slabs and added a little more stress to a layer of buried surface hoar that exists roughly 1-2' deep. This layer has been responsible for the scattered avalanche activity over the past week and a half (including a large avalanche that occurred on Saturday on Twin Peaks). Most areas, especially in the heart of Turnagain Pass, harbor very loose snow over the buried surface hoar and only sluffs are being seen (no slab). It is the areas where the top foot or two of snow is stiffer from wind effect/loading that we need to watch out for. Also, areas where the buried surface hoar is simply deeper due to higher snowfall amounts from our last storm on January 26th, such as in the Portage Valley zone. If choosing to push into the steep and committing terrain, watch for:

-  Areas winds have affected the snow, stiffer snow over softer snow
-  Shooting cracks 
-  Before committing to steep terrain, 
identify terrain traps like gullies, cliffs or rocks below to consider the consequences if even a small slab is released

*Deep Persistent Slab:  Weak snow can still be found near the ground at the upper most elevations in our forecast area, 3,000' - 5,000'. Although triggering a Deep Persistent Slab is very unlikely, it is worth keeping in mind that poor structure does exist at the high elevations. 

Loose Snow 'sluffs':  In most places the snow is very loose and ’sluffs’ easily on the steeper slopes. Watch your ‘sluff’ and be aware of the consequences below you.

Cornices:  Cornices are unpredictable and can break further back along a ridge than expected. Give these features plenty of space.

View of the Twin Peaks Crown on the approach in to investigate on February 5th.

Closer view of the crown. The apex is the trigger point in a shallow rocky spot. The January 21st surface hoar was found to be the weak layer.

 


Mountain Weather

Yesterday started out partly cloudy and became overcast in the afternoon. Easterly winds picked up in the late afternoon blowing consistently into the 20s and gusted as high at 59 mph on Sunburst at 2am. Temperatures rose dramatically in the valley bottoms. Portage went from -19F yesterday at 6am to 32F this morning. Upper elevations stayed in the mid to high 20sF. 

Today expect mostly cloudy skies and light snow showers. Temperatures will be in the 30sF at sea level and the 20sF at upper elevations. Winds will be easterly 5-15 mph gusting into the 20s. Overnight the clouds will move out and temperatures will be in the teens to mid 20sF. Winds will shift to the north and be light.

Tomorrow should be mostly sunny by mid day with temperatures in the teens to mid 20s and light winds. Thursday the sun continues and then there is a chance of snow into the weekend. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  28  .1 62 
Summit Lake (1400')  18  0   0  18
Alyeska Mid (1700')  26  0   0   50

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  22 ENE  18  59 
Seattle Ridge(2400') 25  SE   22  46

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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