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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, January 23rd 2018 4:32 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 remains MODERATE on all aspects above 2,500'. Triggering a very large slab avalanche between 3 and 8+ feet thick is possible. These deep slab avalanches are more likely to be found above 3,000'. Additionally, loose snow avalanches (sluffs) should be expected on steep slopes and be aware of cornice falls along ridgelines. There is a LOW danger below 2,500' where triggering a slab avalanche is unlikely but sluffs are possible.

 


 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

Saturday January 27th, 11:00 am - 12:30 pm: Join CNFAIC forecasters for a FREE hands-on and in-the-snow avalanche beacon practice!! This 1.5 hour informal rescue practice is geared for all user groups. Grab your friends and join us before hitting the hills!! Great intro or refresher! Hosted by the Anchorage Snowmobile Club!  At Turnagain Pass (motorized parking lot) – Look for the blue CNFAIC snowmachine trailer.

Let us know if you see any new avalanche activity that could have been triggered by the earthquake last night. 


Avalanche Problem 1

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Deep persistent slab avalanches remain the primary concern in the advisory area. We know the snowpack structure above 3000' is poor, there is a dense hard slab (3-8+ feet thick) sitting on a variety of weak layers in the mid pack (including buried surface hoar) and old November facets near the ground. Triggering a deep slab is becoming more and more difficult, but is still possible. The most likely trigger spots are thin areas in the snow cover, often near rocks, or where the slope rolls over. High peaks, that see wind, can also be thinner and it is more likely to find the trigger point for a deep slab where some of the slab has been stripped away. 

Key points that keep in mind about our current snowpack:

-  We have a 'low probability, high consequence' situation at the upper elevations for deep slab avalanches. If you do trigger an avalanche it could be huge and unsurvivable.
-  Obvious signs of instability are not likely to been seen before a deep slab is triggered (such as whumpfing and cracking)
-  Remote triggering is possible 
-  This issue can simply be avoided by sticking to terrain below 3000’ (which is a good portion of terrain at Turnagain) or choosing low-consequence terrain in the Alpine

Snow pit on Sunburst that illustrates the buried weak layers in the snowpack above 3000'.

Avalanche on Magnum that ran during the storm last week. Slopes that did not slide at upper elevations are suspect. Photo: Andy Moderow


Avalanche Problem 2

Dry Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

The additional snow we picked up over the past two nights, 5-7" in Girdwood and 1-2" at Turnagain landed on already loose surface snow. The surface snow has been quick to sluff on steep slopes and the new snow will just add to the volume of the sluffs (loose snow avalanches). As the sluffs grow larger they could definitely catch a person by surprise, especially on steep, committing terrain.  

On the flip side if you encounter stiff snow along ridgelines be on the look out for small pockets of wind slab. The wind has been pretty light but loose snow blows around easily. Pay attention to changing conditions.

The loose surface snow, comprised of surface hoar and near surface facets, which is now buried under the new snow.  Photo Allen Dahl

 


Additional Concern

Cornice

Cornices have grown with the last storms; many have fallen, yet many have not. As always, give these features a wide berth and remember they can break further back than expected. A cornice fall at the high elevations could trigger a large avalanche on the slope below. 


Mountain Weather

Yesterday skies were broken with patches of blue and some valley fog rolling in. Temperatures were in the teens to low 20Fs. Winds were light and easterly. Overnight the region picked up 1-2" of snow. 

Today will be mostly to partly cloudy with snow showers in the morning, 1-2" of snow possible. Temperatures will be in the teens and low 20Fs. Winds will be light and shift to the NW. Winds will pick up overnight and skies will clear. Temperatures are forecasted to start falling overnight.

Wednesday looks to be clear, sunny and cold with highs in the single digits. Outflow winds could increase during the day. Overnight temperatures will drop below 0F. Thursday day may even be a bit colder and then temperatures should rise Thursday night as a low moves into the gulf and brings a chance of snow showers for the weekend. 

*Seattle Ridge anemometer is rimed over and not able to collect wind data.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  21  1 0.1 57 
Summit Lake (1400') 14  0.1 16 
Alyeska Mid (1700') 15  2 0.1  47 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  20  ENE  5  15
Seattle Ridge(2400')  24 *n/a  *n/a  *n/a 

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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