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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Monday, January 16th 2017
Created: Jan 16th 5:56 am
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.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
 Show the Complete North American Avalanche Danger Scale
The John Byrne Family
Special Announcement
  • Lost Lake and Primrose are now open for snowmachining! Please STAY ON existing and hardened trail surface through the lower sections of this route.
  • A Winter Weather Advisory is in effect for Hatcher Pass through 8 PM today. The avalanche hazard could rise to high by this afternoon or evening if HP receives the forecasted 8-12 inches of snow. Click HERE to check out today's updated Hatcher Pass Avalanche Center Advisory for more information.
  • Join CNFAIC for our final Fireside Chat on Thursday night, Jan 19th! Aleph Johnston-Bloom will discuss "how has the Turnagain Pass snowpack shaped up" and more - Details HERE.

The Bottom Line

The avalanche danger is MODERATE today in the mountains surrounding Turnagain Pass at all elevations and on all aspects. Wind slab avalanches will be possible to trigger on slopes over 35 degrees that have been loaded by winds. These slabs are expected to be relatively soft, in the 1-2' thick range and could be lower on slopes due to cross-loading. Northern aspects and areas with a shallow snowpack are suspect of deeper instabilities where a triggering a slab up to 2-3’ thick is possible. 

Ice climbers and hikers:  In Portage Valley and other areas where climbing routes and trails sit under avalanche paths, be aware that debris from a natural avalanche above is possible. 

*In the Girdwood Valley, where more snow fell on Friday, there is a heightened danger as a slab avalanche triggered could be 2-3' thick on wind loaded slopes. 


Primary Concern

Yesterday afternoon only a trace of new snow fell, but blowing snow was observed most of the day and weather stations in Turnagain Pass reported moderate Easterly winds 15-30mph during most of the day light hours. This was in addition to moderate Easterly winds that coincided with about 10-12” of new snow the day before. Yesterday’s winds were from the SE on Seattle Ridge and NE at Sunburst, which may have caused slightly different loading patterns on each side of the road. In general Western aspects will be more loaded, but cross loading will range from NW to SW slopes where triggering a wind slab 1-2’ thick will be possible today on slopes steeper than 35 degrees. Several inches of low density snow has fallen overnight without much wind and this may make it challenging to see wind loading patterns. As you travel today be on the look out for obvious signs like shooting cracks and be aware of terrain that may have high consiquences. These slabs are likely to be soft and could be lower on slopes where cross loading may have occurred. 

Red Flags to look for:

  1. Recent Avalanches
  2. Cracks that shoot out from your snowmachine, skis or snowboard
  3. A transition from soft snow to stiffer feeling snow when climbing to exposed areas or higher elevations affected by winds
  4. Texturing of the snow surface (may be difficult to see with a few inches of new snow) 

 ***Loose snow sluffs are also possible on the steeper slopes and these could run further than expected.


Secondary Concern

Northern aspects remain suspect of deeper instabilities where 1-2’ of new snow is sitting on a shallow snowpack with poor structure. Yesterday an observations confirmed evidence of two natural avalanches (occurring some time between 1/13-1/14) on the North facing slopes of Sunburst. Several snow pits on adjacent NW slopes revealed poor structure with some propagation potential in deeper layers of the snowpack. This structure is more common on the Southern end of Turnagain Pass (Magnum to Johnson Pass) where a much shallower snowpack exists. It will be in these areas where triggering a slab in a deeper layer of the snowpack may be easier and possible on any aspect.  

In the lower elevations below 2000’ buried surface hoar is sitting below 8-12” of new snow. Multiple observers yesterday found this layer on Tincan and Eddies. The Alaska Avalanche School found evidence of two small soft slab avalanches on Tincan, possibly remote triggered mid-storm two days ago. These were small, only a foot deep and 20’ wide, but were also on small terrain features. In the lower elevations it may be possible to trigger a soft slab on steep unsupported terrain features or along gully's. This could be more of a concern below treeline in places like Portage or Placer Valley, where ice climbers and hikers should be aware of the terrain above and avoid being in the run-out of large steep slopes.

A North aspect adjacent to one of two crowns found on the North side of Sunburst. Tests results were mixed, but found propagation potential in a uniform layer of facets sitting between two wind slabs 16" below the surface. 

 

Two small soft slabs at 1400' on Tincan that likely released on 1/14 near the end of the storm. Observers dug pits near by and found buried surface hoar to be the weak layer. Prior to this storm buried surface hoar was found below 1500' in many places throughout Turnagain Pass. 

 

 


Additional Concern

Yes, we are still concerned about glide cracks releasing. Most of the cracks we know about are in areas rarely traveled. The exception is in -1 Bowl (Main Bowl) in the Seattle Creek drainage where glide cracks threaten terrain commonly traveled. Keep an eye out for cracks, which can be difficult with new snow, and limit time underneath them.


Mountain Weather

Yesterday skies were overcast becoming obscured by mid afternoon. NE ridge top winds averaged 15 with gusts in the 30’s mph mid-day becoming light from the NW by the evening. Temperatures averaged around 15F cooling to 10F by late evening. Yesterday afternoon to this morning 3-4” of new snow was recorded at Center Ridge and at the mid way station at Alyeska. Other areas of the Pass only received a trace total overnight.

Today an additional 1-3 inches of snow could fall by late morning with scattered snow showers in the afternoon. Winds will remain light from the NW and temperatures will be around 10F dropping near 0F by this evening.   

Cold arctic air over mainland Alaska is expected to bring subzero temperatures to Southcentral, Alaska through the remainder of the week. Skies will be clear with a light Northwest winds. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 14  .3  45 
Summit Lake (1400') .2  15 
Alyeska Mid (1700') 12  .35   43

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 12  ENE  10  35 
Seattle Ridge(2400') SE  12  46 

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

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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