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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, January 24th 2018 4:34 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 is MODERATE on all aspects above 1,000'. Triggering a wind slab in leeward terrain is possible today. Watch for changing conditions. 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 protected from the wind and be aware of cornice falls along ridgelines. There is a LOW danger below 1,000' 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.
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.
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.


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

NW winds are forecasted to pick up today, blowing 15-25 mph with gusts into the 30s. There is light, soft snow available for transport. Watch for wind slabs building on leeward slopes. Avoid steep slopes that looked pillowed and pay attention to changing conditions. Wind flow from this direction can be stronger over Seattle Ridge. It also can be channeled through Turnagain Pass from the South and winds near Taylor Pass can be much stronger. Look for flagging (snow blowing off of ridges), surface snow getting stiffer, cracking and drifting. An observer yesterday triggered a small pocket of wind slab in steep, rocky terrain. There is more snow in Girdwood so expect slabs to be larger. Keep in mind; if winds are stronger than forecasted, natural avalanches may occur. 

Cornices grew during the storms last week. 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.

Snow available for transport today. 


Avalanche Problem 2

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

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. Deep persistent slab avalanches remain a concern in the advisory area. 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
  • 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 above 3000' on Sunburst.


Additional Concern

Dry Loose

On slopes that are protected from the wind expect loose snow avalanches (sluffs) in steep terrain. The additional snow we picked up over the past couple days, 6-10" in Girdwood and 3-5" at Turnagain landed on already loose surface snow. The surface snow has been quick to sluff on steep slopes and the new snow just added to the volume of the sluffs. As the sluffs grow larger they could definitely catch a person by surprise, especially on steep, committing terrain.  Observers are reporting that the sluffs are running long distances and are large enough to have a powder cloud. Winds blowing today could initiate these off of the top of ridgelines.


Mountain Weather

Yesterday was mostly to partly cloudy with a thick fog layer and very light snow showers. Winds were light and shifted from east to west.  Temperatures were in the teens. Overnight temperatures dropped into the single digits. Winds remained light. 

Today skies will be partly cloudy to mostly clear and sunny. Temperatures are forecasted to remain in the single digits and may drop below 0F at upper elevations. Winds will be from the NW 15-25 mph gusting into the 30s. Tonight temperatures drop into the negative with the lows ranging from -6F to -19F. Winds continue from the NW 15-25 mph. 

The cold temperatures continue tomorrow with a chance of snow and NW winds. Temperatures look to warm up into the teens on Friday as a low moves into the Gulf and brings snow showers. However, the overall pattern looks to be mostly cold and dry for the weekend into next week. 

*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')  14  trace 0  56
Summit Lake (1400')  13  15
Alyeska Mid (1700')  13  1.3 0.07   49

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  11  E-W 10 
Seattle Ridge(2400')  10 *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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