Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, March 2nd 2018 5:40 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 1000’ where triggering a wind slab will be possible.  Additionally, old weak layers deeper in the snowpack may be triggered, creating a larger avalanche.  Evaluate snow and terrain carefully. 

**If headed South of Turnagain Pass be aware of recent avalanche activity in Summit Lake and Lost Lake zones. For observations from Summit Lake click HERE and Lost Lake click 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.
Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely


Very Large


Be aware of wind slabs on a variety of aspects due to unusual wind loading patterns and cross loading. Strong Northwest winds this week have transformed a foot of new snow into variable surfaces. Ridgetops are scoured down to old anti-tracks, sastrugi or wind polished snow. Smooth supportable surfaces where the snow is hollow sounding are suspect, especially if the slope is unsupported. Identify terrain features with a pillow-shaped look where triggering a wind slab could break above you. Shooting cracks may not be present until committed to a slope and the whole slab releases. Several weak layers have been preserved ~2 feet below the surface and could propagate a larger avalanche. (More on this below.) Although the sun is not expected today, keep in mind that its that time of year when radiation can make the snow more reactive on Southerly aspects. 

Scoured ridges and wind pillowed snow on Tincan following the big wing event this week. 

Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely


Very Large


Triggering an avalanche 2+ feet thick is possible due to several weak layers buried within our snowpack. More potential exists on the Southern end of Turnagain Pass and Summit Lake zone where a shallow and weaker snowpack remains. This was evident on Wednesday during the wind event where numerous large avalanches released naturally near Silvertip Creek and in Summit Lake. In 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. This structure can be found on all aspects and will be easier to trigger in thinner areas of the snowpack. These slabs could be triggered in softer more protected snow or in places where the snow is harder and more supportable. Assess the terrain for consequences and remember that the bigger the terrain the bigger the consequences. There is still much uncertainty around this avalanche problem. 

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. 

Several observers this week have reported collapsing below 2500' and is likey because of a layer of facets sitting on m/f crust. Photo of W aspect of Cornbiscuit at 2000'


 Large connected crown on a Northeast aspect near Silvertip Creek which released naturally some time between Tuesday and Wednesday during the wind event. 


Mountain Weather

Yesterday was cold, clear and sunny. Day time temperatures warmed into the upper teens F’s from single digits at all elevations. Winds were light and variable and no precipitation occurred. Overnight clouds moved into the area and temperatures increased into the low 20F’s. 

Today expect overcast skies and temperatures to remain in the 20F’s in the alpine with cooler temps at valley bottoms creating some valley fog. A few snow flurries may arrive late afternoon and ridge top winds will remain light from the West. 

This weekend low pressure is tracking just North of us and will favor Mat-Su Valley, but we may see a few inches by Saturday. Some uncertainty exists around winds. Depending on how far North the low tracks, we may see an increase in gap winds again in Coastal areas. Temperatures are expected to range from the teens F to mid 20s F. Skies are expected to clear again on Sunday with another storm is expected on Monday night into Tuesday, but again will favor the Northern areas.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 15  70 
Summit Lake (1400') 29 
Alyeska Mid (1700') 14  61 


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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 17  15 
Seattle Ridge(2400') 16  Variable  13 

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.

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