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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Friday, December 23rd 2016
Created: Dec 23rd 6:05 am
1 Low Alpine / Above 2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
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.
 Show the Complete North American Avalanche Danger Scale
The Bottom Line

A generally LOW avalanche danger exists in the mountains surrounding Turnagain Pass. The surface snow is very loose and triggering loose snow avalanches (sluffing) on steeper slopes should be expected. Triggering a slab avalanche in 'Green light' conditions is still possible. This includes, fresh shallow wind slabs where the winds may be blowing just enough to move snow and old/stiff wind slabs found in very steep rocky terrain.

*The snowpack in the Summit Lake area on the Kenai may be more unstable as whumpfing was reported above 3,000' yesterday. Recent observations HERE. We have little information from the Girdwood Valley and unstable snow could be found in this area as well.

CHRISTMAS WEEKEND OUTLOOK:
Expect avalanche danger to rise with new snow and wind that is forecast for Christmas!


Primary Concern

One more sunny day is on tap (24 seconds more than yesterday) before clouds fill in tomorrow and we wait in anticipation for how the 'Christmas Storm' develops. The winds that were forecast yesterday did not produce at Turnagain, leaving the majority of the snowpack capped with 6-12+" of very soft and loose faceting snow. This has made for good riding conditions, but it has also created a 'base-less' pack in thin areas and early season hazards such as rocks still remain.

Fresh shallow wind slabs:  We are missing data from two of our key wind sensors from last night. Winds may have picked up just enough to form shallow wind slabs/crusts in certain areas. This will be something to look out for today. (The Seattle Ridge sensor is rimed up and the Sunburst station has a battery issue we are working on).

Sluffs:  Watch your sluff if heading for the steep terrain. With such weakly bonded snow on the surface, triggering a loose snow avalanche on slopes 40 degrees and steeper is likely. These sluffs could be quick enough and carry enough momentum/volume to be a concern on the longer sustained slopes.


Secondary Concern

With all the cold weather we have seen in the past 6 weeks, we have developed several weak layers in our thin snowpack. These are composed of two of the 'classic' persistent grain types: facets and buried surface hoar. These weak layers are still present, but the 'slab' that sits on them has decomposed and become faceted in most places - without a slab, you can't have a slab avalanche. The exception are steep rocky slopes where old wind slabs, still stiff enough to be a slab, sit unsupported on weak layers. If you venture to these areas, watch for old stiff wind slabs and if one does release and knock you off your feet, where would you go?

Photo:  Buried surface hoar found under a thick old wind slab. Pit results showed that with a big force, the layer could fail and propagate; unlikely but not impossible in the very steep zones.

 

Surface Conditions??  We are set up again with a very weak foundation once the next snowfall hits.
   

 

 


Additional Concern

Although cornices are pretty frozen in place, breaking off one of these, or a chunk, is still possible while on ridgelines.


Mountain Weather

Yesterday's first day with gaining daylight (11 seconds) was bluebird with light and variable winds. Temperatures were in the single digits in the parking lots at 1,000' and near 10F on the ridgetops.

Today, we should see sunny skies with winds bumping up slightly from the North and West to the 5-10mph range. Temperatures are forecast to be slightly warmer, in the teens at all elevations. 

Looking ahead to the Christmas weekend: A large low pressure is headed our way. Southerly winds should pick up along with high clouds tomorrow morning before the precipitation. The system is bringing warmer air and we could see rain at sea level but snow at 1,000'.

NWS forecast discussion:

"Strong winds coinciding with moderate to heavy
snowfall could produce blizzard conditions in turnagain Pass and
Portage Valley Sat afternoon through Sat night. There is still
some uncertainty as to the degree of warming that will occur in
Portage Valley. Temps in this area could rise into the mid 30s Sat
evening and produce a fairly wet snow or mix and mitigate the
potential for blowing snow. Turnagain pass should safely stay all
snow through Sat night. That said, issued a blizzard watch for
both areas."

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 11  25 
Summit Lake (1400')  0
Alyeska Mid (1700') 13  17 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') Under repair  Under repair   Under repair   Under repair  
Seattle Ridge(2400') 12  Rimed  Rimed   Rimed  

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 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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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