CNFAIC LogoCNFAIC Logo

Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, December 29th 2017 5:28 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
Previous ForecastNext Forecast
BROUGHT TO YOU BY
The Bottom Line

There is a MODERATE avalanche danger today in the alpine, above 3,000’ where triggering a large and dangerous deep slab avalanche is possible due to weak snow near the ground. Triggering an isolated hard wind slab is still possible on steep leeward features or on unsupported terrain in the alpine. Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully.

 

The avalanche danger is LOW at Treeline. LOW danger does not mean NO danger. Pockets of unstable snow are not out of the question if you find yourself in very steep terrain, below 2500’. There is no hazard rating below 1,000’ due to a lack of snow. 

*Please remember your safe travel practices! This includes, exposing one person at a time in avalanche terrain, watching your partners, being rescue ready and having an escape route planned.

**Click HERE for several new observations from Summit Lake.


 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.
0 NO RATING Below Treeline / Below 1,000'
Special Announcement

If you are headed to Hatcher Pass be aware of recent avalanche activity and check out some recent observations HERE


Avalanche Problem 1

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

It has been over a week since a large avalanche was triggered on Pastoral by two skiers traveling below the NW face. If you have been reading the forecast regularly we are not trying sound like a broken record but the message is the same. This snow pack set-up continues to warrant elevated caution and respect. It is a high consequence avalanche problem that is impossible to outsmart and can take a long time to heal. The ingredients for a deep slab avalanche have been found in the upper elevations of our forecast zone, above 3000’ on slopes that did not avalanche in the early December storm cycle. This is a hard slab, 3-5+ feet thick, sitting on top of weak sugary snow (basal facets) near the ground. Observations over the last few weeks indicate this poor structure is widespread across our region in the alpine elevations.

 

When dealing with a deep slab avalanche problem, keep in mind:

  • Large snow covered slopes that do not have large piles of old debris under them are all suspect 
  • Thinner areas of the snowpack (1-2 feet thick) are likely trigger spots as well as scoured areas near rocks   
  • It is possible to trigger this avalanche from below and it could run further than expected 
  • Snow depths are highly variable and there may be more trigger spots than we realize
  • Several tracks on a slope do not mean the conditions are safe. It could be the 2nd, 3rd or 10th person on a slope before someone finds a trigger spot.

 

Weak faceted snow near the ground continues to be reactive and signal propagation potential in test pits in the alpine. Check out a video HERE and observation from Magnum on 12/27/17 HERE

 

Over the last two weeks we have been trying to inventory terrain that has or has not avalanched like this observation sent yesterday from Seattle Creek. Photo taken and annotated by Peter Wadsworth. Check out his observation HERE.


Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Cold temperatures and stable weather this week have been making the snow more brittle and faceting out surfaces. With that said triggering an old wind slab is still possible on very steep terrain in the alpine zone. Places you might find a hard wind slab will be in steep couloirs, large unsupported terrain features, or in thin rocky areas. Triggering a wind slab in the Treeline zone is becoming less likely, but is not out of the question in high consequence terrain. This also goes for a few inches of fast moving loose surface snow “sluff” that could catch you by surprise if you’re not expecting it. Triggering a wind slab could take you for an undesirable ride, and has the potential for initiating a much larger and more dangerous avalanche above 3000'. Be suspect of any slopes that may harbor a deep slab problem in the upper elevations as described above. 

Thin wind slab crowns from a wind event that ended Dec.24 were seen on North and West aspects in Seattle Creek yesterday, as well loose surface snow. Photo by Peter Wadsworth. 


Mountain Weather

Yesterday skies were mostly clear and temperatures along ridgetops averaged in the teens (F) with pockets of colder air at valley bottoms. Valley fog was present along Turnagain Arm. Winds were light and variable and no precipitation was recorded. Overnight thin cloud cover has moved into the region

Today skies are expected to be overcast with light Easterly winds. Temperatures should remain in the mid teens (F) to low 20F’s along ridgetops. Snow flurries are possible, but only a trace of snow is expected. 

A big pattern change is on tap for this weekend. Snow should start falling on Saturday with the intensity picking up late Saturday evening into Sunday morning. Several feet of snow is possible for the Kenai Mountains.  Strong Easterly winds are expected as well as rapidly rising temperatures which could change snow to rain at lower to mid elevations as the storm progresses. 

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 20  30 
Summit Lake (1400') 0 12 
Alyeska Mid (1700') 17  26 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 13  W 11 
Seattle Ridge(2400') 17  variable   14 

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
© 2018 Chugach National Forest Avalanche Information Center. All rights reserved.
FCNFAIC