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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, December 18th 2018 7:00 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 above 1,000'. Soft slab avalanches composed of Sunday's storm snow will be possible to trigger on slopes steeper than 35 degrees. These are most likely to be shallow, 6 to 12" thick, and found near ridgelines and over rollovers. Additional concerns: watch your sluff in steep terrain and avoid traveling underneath glide cracks.

SUMMIT LAKE:  There are more developed weak layers near the ground; increasing the chance a person could trigger a larger slab avalanche. Choose terrain carefully. 


 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

TONIGHT, 6:30 pm: Avalanche Stories from Sunburst at Powder Hound Ski Shop, Girdwood – FREE. Join Chugach National Forest Avalanche Forecaster, Heather Thamm, for an evening discussion on avalanche safety and awareness. This talk will cover some basic things you need to know before going into the backcountry. Expect to hear lessons learned and stories from Sunburst in Turnagain Pass. This talk is geared towards any level of backcountry experience, novice to the seasoned Powder Hound.


Avalanche Problem 1

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Snowfall over the past several days continues to deepen our early winter snowpack and provide some excellent surface conditions. Girdwood Valley has been the most favored for snowfall and has seen over a foot in the past 48 hours, while Turnagain Pass has seen 6-10". The Summit Lake zone has seen roughly 6-8". Very little wind effect during this time has been observed and avalanche activity has been relegated to small pockets of storm slab, soft wind slab and loose snow sluffs. For today, another 1 to 3" of light snow is forecast and will add to these 'surface instabilities'.

If skies open enough for travel to the upper elevations today, keep an eye on the surface conditions. Watch for stiffer snow over softer snow, cracking in the snow and whumpfing (collapsing). The Girdwood Valley could harbor some foot thick pockets of storm slab or wind slab due to the higher recent snowfall amounts. Also, watch your sluff. Sluffs should start getting larger with the cooler temperatures. 

 

A small storm/wind slab pocket was triggered yesterday in Tincan's Common Bowl. Thank you to Drew Petrie for sending in his photo.


Avalanche Problem 2

Persistent Slabs

As we have been mentioning for a while now, in thinner snowpack zones such as Summit Lake and Crow Pass, we are tracking buried layers of facets, crusts and buried surface hoar that sit 1-3' under the snow surface. These layers are most prevalent in the mid-elevations (2000’ – 2700’). Snow pit data and a lack of avalanche activity has been pointing to an unlikely chance for an avalanche releasing in these deeper layers. However, as we push out into more and more terrain, we need to keep in mind the snowpack could have some surprises lurking. 

Snow pit on Tenderfoot, in the Summit Lake area, from Sunday shows buried surface hoar deep 2' below the surface that will react with a lot of force. 


Additional Concern

Glide Avalanches

Glide cracks are moving. We have had several reports that cracks are opening. Glide cracks we know about are on Sunburst's SW face under the weather stationSW face of Tincan Proper, Gold Pan area (behind Cornbiscuit/Magnum) and a crack that did release in the Johnson Pass area. These cracks can release at any moment. They are not associated with human triggers and the best way to manage the hazard is to avoid being on or beneath slopes with cracks. 


Mountain Weather

Yesterday:  Partly cloudy skies with some valley fog were over the region. Intermittent flurries overnight has added a trace to an inch of snow at Turnagain Pass and 1-2" of snow in the Girdwood Valley. Ridgetop winds were easterly yesterday, 5-10mph, and have been light and variable overnight. Temperatures remain near 20F along ridgelines and the upper 20'sF at sea level.

Today:  Mostly cloudy skies with a chance for 1 to 3" of cold, low-density snow are on tap today. Ridgetop winds should be northerly in the 5-10mph range. Temperatures will remain winter-like, in the 20'sF at sea level and in the teens along ridgelines. Tonight, we may see a bump in snowfall rates with another 2-4" of low-density snow possible with this light northerly flow. 

Tomorrow:  Light snow showers should cover the region Wednesday. Models are showing a low-pressure forming just south of Seward that looks to shift winds back to the east and pump in a bit of moisture. Snow numbers for tomorrow look to be in the 3-6" range. 

*Seattle Ridge anemometer (wind sensor) is rimed over and not reporting.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 21  trace  36 
Summit Lake (1400') 20   0 15 
Alyeska Mid (1700') 21 1-2"  .1 - .2  27 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 19  21 
Seattle Ridge(2400') 20  *no data  *no data   *no data  

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, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of 4.3.19
Placer River: ClosedClosed as of 3.20.19 due to lack of snow.
Skookum Drainage: ClosedPlacer access closed as of 3.20.19 due to lack of snow.
Turnagain Pass: ClosedClosed as of 5/6. Thanks for a great season all, see you next winter!
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Closed
Lost Lake Trail: ClosedClosed as of 3.22.19 due to lack of snow
Primrose Trail: ClosedClosed as of 4.3.19 due to lack of snow
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: ClosedClose as of 5.1.2019
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
Summit Lake: Closed

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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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