Avalanche Advisory

Turnagain Area Avalanche Advisory
Sunday, February 22nd 2015 7:00 am by Graham Predeger
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger is CONSIDERABLE today above 2,000’ where wet snow has increased the stress on an untrustworthy persistent weak layer.  Add a person into the mix and human-triggered avalanches are likely on slopes greater than 35 degrees.  Moderate Easterly winds are also increasing the likelihood of wind slabs 12-24” deep in the upper elevations.

The danger is MODERATE below 2,000’ as it is important to recognize that an avalanche initiated in the Alpine can entrain enough snow in isolated areas (funneled terrain) to run debris well below our current snow line.  This is an “overhead hazard” and important to keep in mind in places such as Portage Valley or the Byron Glacier trail.

 Show the Complete North American Avalanche Danger Scale
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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

Iron those Carhartts, break out the sequins, and dust off the bolo…its Snowball time! Please join the Friends of the Chugach National Forest Avalanche Information Center and Alaska Avalanche School at Taproot for an “Alaskan Formal” night at 7pm on February 27th.  You won't want to miss this event!

Avalanche Problem 1

A perfect recipe for dangerous avalanche conditions exist in the 2,000 – 3,000’ elevation band where a uniform weak layer of faceted snow lies in wait 6” to 3+’ below the surface.  Level 2 avalanche course students were experiencing large collapses (whumphing up to 100’ radius) on this faceted layer yesterday, proving there is a significant amount of energy within the weak layer.  This translates to good potential for an avalanche to propagate across a slope if initiated. 

Yesterday’s storm has increased the load overlying this weak layer with wet snow falling above 2,000’ (and rain below).  Human triggered avalanches are likely on slopes steeper than 35 degrees.  This most recent load may just be enough to initiate a natural avalanche cycle as well, though visibility yesterday was hampered to the point where no natural avalanches were observed.

If you travel in the backcountry today, it’ll be imperative to stick to mellow terrain and avoid steeper connected slopes or runout zones.  If you are in a runout zone or on a mellow slope connected to a slope greater than 35 degrees, you’re in avalanche terrain.  Remember, you cannot necessarily manage the weather or the snowpack right now but you can always manage your terrain choices to ensure a safe day in the backcountry.

Avalanche Problem 2

Moderate Easterly winds combined with new snow in the upper elevation start zones have been, and will continue to actively build fresh wind slabs 12 – 24” today on leeward slopes.  These could be a problem in and of themselves but also have the potential to step down into deeper weak layers, possibly creating large avalanches.  

Additional Concern

Below 2,000’ what snow that is on the ground has been well adjusted to the recent rain and warm temperatures.  The greatest hazards at these lower elevations come in the form of avalanches initiating in the mid to upper elevations and debris travelling in funneled terrain well below our rain/ snow line. 

Moreover as bizarre as it is to say in late-February, early season conditions do exist.  Thin snowpack, icy approaches and water crossings are all real hazards right now in the lower elevations.

Mountain Weather

Yesterday was marked by another warm, wet North Pacific low pressure system that brought steady rain to southcentral Alaska below about 2,000'.  Ridgetop temperatures were in the high 20's with sustained winds in the 20-35mph range from the NE.  Girdwood appears to be the precip winner with 1.16" of water in the past 24 hours as temperatures remained in the high 30's at sea level throughout the day.  

More warm air is on tap across our region though rainfall looks to be more intermittent today than yesterday.  Expect temperatures to be in the upper 30's at 1,000' with up to a quarter inch of water forecasted.  The rain/ snow line again will be somewhere in the 2000 - 2200' range today with ridgetop winds out of the east in the 15 - 30mph range.

On Monday the weather models hint at (relatively) colder air moving in from the west coupled with continued moist flow though precip amounts are quite nominal at this point.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 35  0  .3   42 
Summit Lake (1400') 35  0  .3
Alyeska Mid (1700') 35   1/ rain  1.16  25


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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  27  n/a n/a  n/a 
Seattle Ridge(2400') 29  n/a 23  58 

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: Oct 05, 2019 )

Glacier District
Johnson Pass: ClosedClosed
Placer River: ClosedClosed
Skookum Drainage: ClosedClosed
Turnagain Pass: ClosedClosed
Twentymile: ClosedClosed
Seward District
Carter Lake: ClosedClosed
Lost Lake Trail: ClosedClosed
Primrose Trail: ClosedClosed
Resurrection Pass Trail: ClosedClosed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor: ClosedClosed
South Fork Snow River Corridor: ClosedClosed
Summit Lake: ClosedClosed

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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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