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Avalanche Advisory

Turnagain Area Avalanche Advisory
Saturday, February 24th 2018 4:47 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 1,000' on all aspects. Triggering an isolated wind slab or a more connected persistent slab 1-2’ deep is possible today. Additionally, weak layers deeper in the snowpack may still be triggered, creating a larger avalanche. With new snow and wind in the forecast today pay attention to changing conditions. 

Read the Summit 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.
2 Moderate Treeline / 1,000'-2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Special Announcement

Hatcher Pass users:  Dangerous avalanche conditions exist in this area. Several close calls have occurred including one person caught, carried and partially buried yesterday. Please see the Hatcher Pass Avalanche Center forecast before heading that way. 

The final Near Miss Report from the avalanche on Twin Peaks that occured Saturday, February 3rd is available HERE. Thanks to all involved for sharing their description of events and lessons learned. 

 


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering a slab avalanche 1-2+ feet deep remains possible above 1000’ due several weak layers buried within the snowpack. A layer of buried surface hoar from Jan. 21st continues to show signs of reactivity in the upper elevations, and a layer of facets over a melt-freeze crust is suspect in the mid elevation band. The slab ranges from hard to soft depending on exposure to recent winds.  The Northwest winds overnight Thursday blew the 3-4” inches of new snow into stiff wind crusts. As noted yesterday this wind direction can funnel through Turnagain Pass from a variety of directions causing unusual wind loading patterns that were evident traveling on Sunburst. Another 4-5" of light snow fell overnight and today we may pick up an additional 2-4." This combined with escalating Northwest winds may add more slab and stress to the snowpack. Be suspect of hard snow under the new soft snow, especially where the slab is fully supportable or hollow sounding. Red flags like shooting cracks or “whumpfing” may not be present before a slope releases. Evaluate the terrain for consequences and be aware of places that haven’t seen much traffic. These less traveled places are more suspect for triggering a more connected slab. 

Deep Persistent Slabs: Keep in mind that there are deeper persistent layers that could 'wake up' if you find the wrong spot above 3,000' in the Alpine. At these high elevations, old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is most pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass. 


Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering a wind slab is possible today on steep unsupported terrain features where winds have been transporting snow. These slabs could range from tender and soft with new snow overnight being moved by winds today or hard and supportable due to the strong winds Thursday night. Remember the hard wind affected snow will be under the new snow. It may be harder to pick out wind loaded areas with the fresh coating of snow on top and slab could release from above once committed to a steep slope. 

Sunshine:  If the clouds break earlier than expected today remember that it is that time of year when we need to pay attention to the sun.  The sun can heat up Southerly aspects, and melt surface snow and cause small point releases in the loose new snow. This will be more of a concern if winds are calm today, which may be the case this afternoon. This heating can also cause a slab sitting on a weak layer to become more reactive. Avoid steep solar aspect if you notice the surface snow becoming moist or you see roller balls or point releases under rocks. 

Wind effect on the Sunburst ridge yesterday

 Wind crust on Sunburst easily sliding off of snow below. New snow and wind loading today could turn this into a wind slab. 


Mountain Weather

Yesterday started clear and became cloudy by the evening. Temperatures were in the teens to low 20Fs. Winds started out Northwesterly and gusted into the 60s on Seattle Ridge in the morning. They switched to the Southeast overnight and blew in the teens gusting into the 30s. 

4-5" of light snow fell overnight with an additional 2-4" in the forecast today. Temperatures will be in the teens to mid 20Fs. Southwinds winds are forecast to shift back to the Northwest in the afternoon blowing 10-20 mph with gusts into the 30s.  

Sunshine is on tap for tomorrow and then a chance of snow again Sunday.  This pattern of smaller storms followed by sunshine looks to continue into next week. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 22   4  0.3  68
Summit Lake (1400') 18    5  0.3  30
Alyeska Mid (1700')  20     5  0.2  61

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  10  W-E  8 38 
Seattle Ridge(2400')  16 NW-SE  20   62  

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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