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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, February 19th 2019 7:00 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 due to recent snowfall and wind loading. Human triggered slab avalanches 1-2' thick are possible on slopes 35 degrees and steeper, especially in wind-loaded terrain. Additionally, give cornices a wide berth and avoid travel under glide cracks. Watch for changing conditions and look for signs of instability. 

GIRDWOOD / PORTAGE / PLACER: More snow fell north of Turnagain Pass over the weekend. Slabs will be deeper and there is more snow available for wind transport today. 

SUMMIT LAKE / JOHNSON PASS:  This area has a very poor snowpack structure with multiple weak layers. Triggering an avalanche in recently wind loaded terrain has the potential to initiate a more dangerous slab, breaking deeper in the snowpack. 

SEWARD / LOST LAKE:  Recent snow and wind loading has impacted this region as well and triggering slab avalanches is possible today. Look for signs of instability. 

 


 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.
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.
Special Announcement

Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Northwest winds are forecast to impact the advisory area today blowing 10-20 mph with gusts into the 30s and 40s. There is snow available for transport. Watch for blowing snow and expect slabs to become more stiff and connected in the Alpine. This wind pattern is opposite the loading direction from the storm this weekend. Be on the lookout for drifting and cracking and listen for hollow sounding snow indicating harder slab over soft snow. Observers yesterday reported an 'upside down' snowpack from the weekend's snow and wind, hand pits failing on isolation and triggering small steep convexities. There was one remotely triggered small slab in Common Bowl on Tincan. Steep, unsupported slopes (35 degrees and steeper) that are wind loaded will be the most suspect today. In addition pay attention to direct sunshine. Steep southerly slopes protected from the wind may see some roller balls and may be more prone to triggering with warming as the recent storm slab becomes more cohesive. Remember slab depth may be thicker on the northern end of Turnagain Pass, in Placer, Portage and Girdwood. More snow fell in this part of the advisory area over the holiday weekend. Practice safe travel and evaluate snow and terrain carefully. Cornices are looming large in some of the Alpine terrain. Give them an extra wide berth as they often break farther back than expected.

 

Remote triggered small slab on Tincan Common, 2-18-19. Photo: Amanda Compton

 Hand pit failing on isolation on Sunburst at 2700', 2-18-19. 


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Periphery zones such as Summit Lake and Johnson Pass harbor a poor overall snowpack structure with a variety of weak layers. From Girdwood to Turnagain Pass roughly 2-3' below the snow surface sits a layer of buried surface hoar.  Although these persistent weak layers have not been reactive lately, additional load from recent snow and increasing winds may start to tip the balance. It is good to keep in mind that triggering an avalanche today could to step down into old weak layers and initiate a larger more dangerous slide. This is more likely in and around Summit Lake where the structure is the most suspect. 


Additional Concern

Glide Avalanches

Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.


Mountain Weather

Yesterday: Broken skies with periods of light snow showers, sunshine and patchy fog. Winds were easterly 5-15 mph gusting into the 20s. Winds became calm overnight and shifted to the west. Temperatures were in the 20Fs at upper elevations and mid 30Fs at sea level. 

Today: Mostly cloudy becoming mostly sunny. Northwest winds increasing this morning to 10-20 mph with gusts into the 30s and 40s, decreasing tonight becoming light and westerly. Temperatures in the 20Fs and low 30Fs. Cooling in the afternoon into the evening. Temperatures will be in the teens overnight with mostly clear skies. 

Tomorrow: Mostly cloudy skies as the next front moves into the area. Winds shift to the east and increase to 10-20 mph with gusts into the 30s. Temperatures will be in the 20Fs.  Snow showers are forecast to start in the afternoon and increase overnight into Thursday. 

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  29     60 
Summit Lake (1400')  29   0.1    29 
Alyeska Mid (1700') 30  0.1   60

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 20  variable  26 (SE)
Seattle Ridge(2400') 25  variable   6    31 (NW) 

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
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