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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, January 25th 2018 5:24 am by Wendy Wagner
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 on all aspects above treeline. Fresh wind slab avalanches, up to a foot thick, could be found and triggered on leeward slopes. In addition, triggering a very large slab avalanche between 3 and 8 feet thick is still possible above 3,000'. 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

 


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

The Northerly winds that were forecast to hit the area yesterday only bumped up slightly along most ridgelines. Stations reported averages from the North and West in the 10-15mph before settling down last night. This is good news for limited wind slab development. However, areas like Portage Valley, Seattle Ridge and Crow Pass are suspect to have seen stronger winds and subsequent new wind slabs. We had a report of two small slab avalanches (believed to be new yesterday and likely wind slabs) that released on Maynard Mountain in Portage Valley.

With plenty of loose surface snow to blow around, be on the lookout for wind slabs. Textured surface snow, rounded and pillow-like surfaces and feeling for stiffer snow over softer snow are all signs the winds have visited. Cracking in the snow around you will be a sure sign you have found a wind slab. Any fresh slabs are expected to be shallow, a foot or less thick, and could be touchy. These are most concerning if they knock you somewhere you don't want to go, like over cliffs.


Avalanche Problem 2

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Unfortunately, the snowpack structure above 3000' is poor. Specifically, there is a 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. Deep persistent slab avalanches remain a concern on these upper elevation slopes. Triggering a deep slab is becoming 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. South of Turnagain Pass the snow cover is thinner, triggering a slab in this area could be more likely as well. Remember, this is a 'low probability, high consequence' situation and no Red Flags are likely to been seen (such as whumpfing and cracking). Remote triggering is possible and there may already be tracks on the slope. 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.

Snowpack structure at 3,600' on North facing Tincan Ridge below. We found the poor structure in our pit, meaning the weak layers are there, but they were either hard to get to fail or did not want to propagate. This is a good sign, but as long as these weak layers are present, the chance a person can trigger a deadly deep slab remains despite snow pit results...

 


Additional Concern

Dry Loose

Watch your sluff. Cold temperatures are ramping up the 'faceting process' in the top foot of the snowpack and sluffs are getting bigger and faster day after day. *Once we do get a new load of snow on this very weak snow, you can imagine just how hard that new snow will be to stick (today's good riding is tomorrow's avalanche producer...).

These skier/boarder initiated sluffs on Tincan Proper ran to valley floor in some cases with small powder clouds.


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Mountain Weather

Very cold and mostly clear skies were had yesterday. Ridgetop winds were variable blowing on Seattle Ridge into the teens from the North and only light from the West on Sunburst. Temperatures were in the single digits to the minus single digits at all elevations. No precipitation has been recorded for two days. 

Today, another cold and partly sunny to cloudy day is on tap. A chance for a few snow flurries is possible with up to an inch of accumulation by this evening. Temperatures could climb from the negative single digits, where they sit this morning, to the teens at the lower elevations - but the upper slopes will remain in the -10 - 0F range. Ridgetop winds are forecast to be light from the North and West in the 5-15mph range.

This evening and into Friday, Easterly winds will pick up and bring warmer temperatures (teens) and a chance for 2-4" of snowfall. 

* THANK YOU to the snowmachiners that cleared off Seattle Ridge weather station yesterday!! 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 57 
Summit Lake (1400') 15 
Alyeska Mid (1700') 50 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') -4   10
Seattle Ridge(2400') -2  NNE    18 

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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