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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, February 15th 2019 7:00 am by Heather Thamm
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 2000'. Triggering an isolated wind slab will be possible on steep, leeward terrain features. Triggering a larger slab avalanche 1-3' thick is becoming more unlikely, but not out of the question for Turnagain Pass. Give cornices a wide berth, and avoid travel under glide cracks.

SUMMIT LAKE / JOHNSON PASS: Areas south of Turnagain Pass harbor a thinner, weaker snowpack with multiple weak layers present including buried surface hoar. This zone has more potential for triggering a large slab avalanche 1-3’ thick. Choose terrain wisely. Whumpfing, shooting cracks and recent avalanches are 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.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Special Announcement
  • Heading to Hatcher Pass? Be sure to check out the Hatcher Pass Avalanche Center mid-week snow and avalanche summary and observations page for current conditions.
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Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Two days of strong Northwest winds 20-40mph blew most of the loose snow either into the atmosphere, eroded old tracks, or packed it into hard wind slabs and wind crusts. Dozens of small wind slabs were triggered naturally during this event, and several human triggered wind slabs were observed including one yesterday in Lynx Creek. Today triggering an isolated wind slab will be possible in very steep terrain. Smooth hard supportable snow on steep convex and unsupported features will be the most suspect. Wind slabs could be small and shallow or larger if they step down to older weak snow. More on this below. Also keep in mind the Northwest wind direction creates unusual wind loading patterns opposite our normal Easterly storm track direction. Aspects that are typically more shallow and scoured may be more loaded than usual.

CORNICES: Cornices are large in some of the Alpine terrain. Winds may have added additional stress this week. Give them an extra wide berth as they often break farther back than expected. 

 

Wind eroded tracks along Seattle Ridge yesterday are a good example of how strong wind over the last few days have moved a lot of snow. 


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Strong Northwest winds over the last two days were a good test of the snowpack. Summit Lake proved to be the most active, which isn’t a surprise due to an overall thinner and weaker snowpack. Dozens of small natural wind slab avalanches occurred in steep channeled terrain, and some stepped down to older layers producing larger avalanches. Most of this activity occurred on East facing aspects of Fresno Ridge to Gil Patrick and further South to the Sterling Wye. In Turnagain Pass very little avalanche activity was observed other than a few wind slabs in steep terrain and nothing larger that we know of.

What about the MLK buried surface hoar we’ve been talking about for the last few weeks? Is the weight of a person or snow machine still able to trigger this widespread weak layer that sits 1-3’ below the surface? Some uncertainty does remain, but it is becoming more and more unlikely with time. We know buried surface hoar is still lurking, but it has been 10 days since an avalanche was triggered  on this layer in Turnagain. Strong winds over the last few days have added additional stress in some places and this should still be on your mind if you are out searching for soft snow. 

If you’re headed into the mountains keep in mind:

  1. Wind loaded steep features, large connected and unsupported slopes are the most suspect.
  2. Eastern aspects that typically harbor a weaker structure may be more loaded than usual.
  3. There is more potential for triggering this problem in Summit Lake, Johnson Pass and Lynx Creek due to a generally thinner and weaker snowpack.
  4. Use safe travel protocol. Expose only one person at a time (this includes paying attention to other groups in the area), watch partners, stop in safe zones and be rescue ready

Pit results yesterday on Seattle Ridge showed the MLK (Martin Luther King Day) buried surface hoar layer present but unreactive.

 

 

Several pockets of wind slab on the flank of two East facing gullies of Summit Peak stepped down into older snow closer to the gut.

 


Additional Concern

Glide Avalanches

Glide cracks are on the move and becoming more active this week. Two glides have released this week, one near the Hope Wye and another in Girdwood Valley. Several glide cracks threaten popular routes on the South facing slopes of Lipps and Magnum. There is also a new glide crack opening on Seattle Ridge on Repeat Offender in a zone that is commonly high-marked. 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 identify their location and avoid traveling on slopes directly below glide cracks.

 

New glide crack opening up on Seattle Ridge just South of the up-track. 

 


Mountain Weather

Yesterday: Skies were clear and sunny. Temperatures at all elevation dipped into the single digits F. High temps near sea level were in the teens F. Ridgetops and channeled valleys experienced Northwest winds 5-15mph with gusts 20-30mph. No precipitation fell. 

Today: Expect another day of clear and cold weather. Temperatures will remain in the single digits this morning, but will gradually increase throughout the day in sync with a weather pattern shift. Low pressure moving into our region will bring temperatures back into the teens and low 20F's overnight. Ridgetop winds 5-15mph from the Northwest will diminish and shift mid-day to an Easterly directly. 

Tomorrow:  The first of several storms will move into Southcentral Saturday and a second storm will arrive on Sunday. Cold air from the North will keep temperatures at or below freezing. At this point there remains a lot of uncertainty around quantity of snow accumulation, but the Southwest flow typically favors Cook Inlet and Hatcher Pass. Sunday's storm looks more promising for the Eastern Kenai Mountains. Strong Easterly winds will accompany these storms. Expect ridgetop winds to build to 30-40's mph by Saturday evening. 

*The Seattle Ridge anemometer was replaced yesterday and has been recording wind data since 1pm, Feb 14. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 11  57 
Summit Lake (1400') 24 
Alyeska Mid (1700') 50 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') WNW  26 
Seattle Ridge(2400') *NW  *4  *10 

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: Mar 22, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Open
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: Open
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Open
Lost Lake Trail: ClosedClosed as of 3/22. Unfortunately HEAVY rain over the past week has washed much of the snow off the lower stretches of this trail.
Primrose Trail: OpenPlease stay on trail to avoid resource damage through forested areas.
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: Open
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
Summit Lake: Open

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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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