Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, March 1st 2018 5:43 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 at all elevations due strong winds over the past two days. Human triggered wind slabs 1-2' thick will be possible, and radiation from the sun could make slabs easier to initiate in the afternoon on solar aspects. Additionally, old weak layers deeper in the pack may be triggered, creating a larger avalanche.  

Numerous natural avalanches occurred in Summit Lake yesterday and a human triggered avalanche occurred the day before on Tenderfoot. Read the Saturday Summit Summary HERE and current observations 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.
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.
Special Announcement

Lost Lake Trail, Primrose Trail, South Fork Snow River Corridor and 20 Mile are all open for motorized use. At 20 Mile please cross the railroad tracks at the designated spot as you leave the parking area.

If heading to Lost Lake area check out several observations describing two snowmachine triggered avalanches that occurred over the last two days HERE. 

Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely


Very Large


Yesterday a big wind event impacted Southcentral Alaska and unfortunately Turnagain Pass was not spared. Large plumes of blowing snow were observed on most ridgetops as well as scouring, anti-tracks, wind sculpted snow. We received several reports of small natural wind slabs releasing on the SW face of Tincan yesterday and could see fresh debris in a Northern chute of Corn Biscuit. Numerous wind triggered avalanches occurred in Summit Lake area as well as a large avalanche on a Northern aspect near Silvertip Creek. (More on this below.) Active wind loading occurred on the SE face of Seattle Ridge, but on the other side of the road the wind direction was funneling through terrain from the South at times. Be aware of wind slabs on a variety of aspects due to unusual wind loading patterns and cross loading. Triggering a hard supportable wind slab will be possible and could step down to a deeper persistent layer and propagate along larger slopes. Identify smooth or pillow-shaped surfaces in steep terrain where triggering a wind slab could break above you, once committed to a slope. Supportable surfaces where the snow is hollow sounding should also be suspect. 

Sunshine:  If winds are calm today radiation from the sun could make wind slabs more reactive in steep terrain on Southerly aspects. Pay attention to surface snow melting or point releases near rocks in steep terrain. The sun can also add stress to cornices and make them easier to trigger. 

Strong winds blowing snow onto a Southern aspect of Tincan yesterday, but wind loading was also observed on Northern aspects yesterday. 


 Winds loading the SE face of Seattle Ridge yesterday.

Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely


Very Large


Triggering a large slab avalanche 2+ feet thick is possible due to several buried weak layers within our snowpack. Recent snow this week combined with strong winds have added stress to the snowpack. More potential exists in places with a shallow snowpack like the Southern end of Turnagain Pass and Summit Lake zone. This was evident yesterday during the wind event where numerous large avalanches released naturally near Silvertip Creek and in Summit Lake. In the heart of Turnagain Pass we have been tracking several weak layers buried 1-2 feet deep  (facets and buried surface hoar) and both have been reactive in stability tests. The tricky part about this avalanche problem is that these slabs are hard and supportable and may be difficult to assess. Yesterday we investigated a human triggered slab avalanche on Tenderfoot (from Tuesday) where the slab was disguised as hard sastrugi. Obvious clues like “whumpfing” or shooting cracks may not be present before a slope releases. Assess the terrain for consequences and remember that the bigger the terrain the bigger the consequences. 

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 also more pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass. 

Two large natural avalanches observed yesterday on the ridge East of Silvertip Creek, NE slope 


Facets over a rain crust have been showing propagation potential in the mid elevation zone. This pit was in the Center Ridge area yesterday. Photo by Nick D'Alessio 


Mountain Weather

Clear skies and strong NW winds impacted Southcentral, Alaska yesterday. Seattle weather station recorded 30-50mph NW wind most of the day, while Sunburst station was more protected from this direction and recorded West winds in the 10-30mph range.  Overnight NW winds decreased to Moderate. Temperatures in the upper elevations remained in the single digits F all day yesterday while lower elevations increased into the teens F’s during the day. No precipitation was recorded. 

Today will start out with clear skies becoming cloudy this evening. Winds will continue to mellow out and become light from the NW. Temperatures may be inverted in some areas with single digits in valley bottoms and ridge tops in the teens F to low 20F’s. No precipitation is expected. 

Into this weekend temperatures will gradually increase into the 20F’s at all elevations and there’s a chance for snow showers Saturday. Winds are expected to remain the light to moderate range. 

*Center Ridge and Summit Lake weather stations are currently down and data after 1pm (2/28/18) is unavailable.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') *16  72 
Summit Lake (1400') *14  30 
Alyeska Mid (1700') 13  62 


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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  W 10  39 
Seattle Ridge(2400') 11   NNW 22  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: 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.

If you have comments or questions regarding CNFAIC operations or winter recreation management, please email
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