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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Tuesday, December 12th 2017
Created: Dec 12th 5:13 am
4 High Alpine / Above 2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
4 High Treeline / 1,000'-2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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Special Announcement

Elevated avalanche danger remains throughout Southcentral, AK due to continued stormy weather. If you are headed to Hatcher Pass check out hpavalanche.org and for Valdez, valdezavalanchecenter.org Also, there have been reports of unstable snow and human/natural triggered avalanches near Petersville and the Dutch Hills area.


The Bottom Line

The avalanche danger is HIGH due to continued heavy rain, wet snowfall and strong winds. A very potent warm and wet storm has saturated the snowpack and caused a natural wet avalanche cycle below 3000’. Today natural and human triggered wet slab avalanches are likely at Treeline and storm snow avalanches are likely in the Alpine. Today is a good day not to go into the mountains. Travel in avalanche terrain is NOT recommended

Below 1,000’, where little snow exists, there is a CONSIDERABLE avalanche danger for debris running into steep or channeled terrain.

**Summit Lake also has elevated avalanche danger and the weekly summary can be found HERE.


Primary Concern

A series of warm and wet storms have created a widespread avalanche cycle across our forecast zone. Over the last three days 3.1 inches of rain has saturated the mid elevations (treeline zone) and rain/snow line has fluctuated between 2000’ and 3000’. A brief window of good visibility yesterday allowed for a look around Turnagain Pass where dozens of recent wet slab avalanches have occurred on all aspects below 3000’. These avalanches have been releasing near the ground on a well documented weak layer of faceted snow. The most interesting (and scary) avalanches observed yesterday were on the West facing terrain of Tincan below 2500’, an area many folks go when the avalanche danger is elevated. This avalanche cycle speaks to the powerful nature of a saturated snowpack and is a reminder that even small terrain features are suspect. An avalanche of this kind, if triggering from below or in a terrain trap, would be unsurvivable. Today another .5” of rain is expected below 2000’ combined with moderate to strong Easterly winds. High avalanche danger will continue through today and will remain elevated until the snowpack has a chance to drain or freeze. Travel in avalanche terrain is not recommended. 

Recent wet slab avalanches were observed yesterday afternoon on the West facing terrain of Tincan. 

 

 Recent avalanches on Northern and Western aspects of Corn Biscuit.

 

Dozens of slabs have ripped out to the ground on the SE face of Seattle Ridge and most of the gullies are filled with debris. As of yesterday the uptrack on Repeat Offender remained intact. 


Secondary Concern

In the Alpine, wet and heavy snow is falling, which becomes drier with elevation. From our rainfall totals at the snow stations over the last three days, we can expect around 3’ of snow has accumulated in the alpine. Cornices are building and the weak pre-existing snowpack continues to be loaded. Storm snow avalanches that include storm slabs, wind slabs and cornice breaks all can be expected today at the high elevations. This snow may also overload and tip the balance of the weak snow sitting near the ground and create a very large avalanche, taking most of the snowpack with it. This size avalanche could run into the lower elevations in steep or channelled terrain.  

Again, the message is simple for today, avoid avalanche terrain. This means steering clear of all slopes 30 degrees and steeper including your exposure to runout zones.


Mountain Weather

Yesterday another 0.5” of rain fell in Turnagain Pass and .94” of rain Girdwood. Temperatures remained above freezing, mid 40F’s at seal level and mid 30F’s at 1000’. Easterly ridge top winds averaged in the 20’s with gusts in the 60’s. Temps cooled briefly last night bringing snow/rain line to 1700’ where a few inches of wet snow has accumulated at mid elevation weather stations.  

Today another 0.5” of rain is expected throughout the day and rain/snow line is expected to be around 2000’. Easterly ridge top winds could range from 20-30mph with gusts in the 40’s. Tonight continued rain showers are expected. 

Stormy weather in the form of rain showers and strong Easterly winds is anticipated through Wednesday afternoon. Winds should diminish tomorrow afternoon and temperature will gradually start falling. Thursday into Friday we may see freezing temperatures again at sea level with a possibility of scattered rain and snow showers. 

*Center Ridge snow depth at 6am is estimated due to depth guage sense experiencing noise.

** Sunburst weather station data is from 6am - 8pm (12/11/17) due loss of battery power yesterday evening.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 34   3 0.5  *28 
Summit Lake (1400') 34   0 0.1  9
Alyeska Mid (1700') 35  .94  16 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') **26  **ENE  **28 **62 
Seattle Ridge(2400') 30  ESE   21 50 

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: Dec 08, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedRain and snow have fallen in Turnagain Pass this week, but not enough to open for snowmachining. Continue to check back to this site for updates.
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail is expected to open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
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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