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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, February 7th 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 remains a 'scary' MODERATE on slopes above 2,000’. Triggering a large unsurvivable slab avalanche 2-3’ thick is possible on steep slopes. This kind of slab can be triggered remotely from a ridge, similar to an avalanche triggered yesterday on Eddies. In addition look for signs of windloading and roller balls on solar aspects. Avoid cornices and glide cracks and watch your sluff. Identify high consequence terrain and practice safe travel protocols. A lot of uncertainty exists in our current snowpack.

SUMMIT LAKE / JOHNSON PASS: A variety of weak layers exist in the snowpack and human triggered slab avalanches 1-3' thick remain possible. Choose terrain wisely.

LOST LAKE: We received a report of a human triggered avalanche yesterday, which occurred on Saturday on Exit Glacier trail. New snow and winds over the weekend have elevated the avalanche danger near Seward and Lost Lake. This area has very little snowpack info and extra caution and conservative decision making is necessary.


 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.
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Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

If you are headed to Turnagain Pass you get to start your day with a red flag warning, a recent avalanche. Yesterday two skiers remotely triggered an avalanche on the Southwest face of Eddies from 30’ away on a flat ridge. They had just dug a pit and found the culprit, buried surface hoar, one foot below the surface. Multiple tracks were present along the ridge before the avalanche released no obvious signs like whumpfing were observered.

This is the same buried surface hoar “MLK BSH” we’ve been talking about for two weeks since it was originally buried on Matin Luther King Day. This weak layer is widespread across our forecast zone and has been responsible for numerous large human triggered avalanches over the last 10 days, all in Seattle Creek drainage, and not visibile from the road. So far no one has been caught or carried and most of these avalanches have been triggered remotely from an adjacent ridgeline. Yesterday was the first human triggered avalanche on the non-motorized side of the road. Today’s sunshine and soft snow could make it tempting to push into steeper terrain. Keep in mind incremental loading over the last week and period of stronger winds on Monday may have added more stress to this weak layer. Don't forget this is a challenging avalanche problem to evaluate and manage, and warrents extra caution.

Keep in mind as you travel today:

  1. The weak layer is around 2-3 feet under your feet or snowmachine, but triggering this weak layer will be more likely in a thinner part of the slab.
  2. No obvious signs of instability like “Whumpfing” are expected until a slope releases.
  3. Previous tracks on a slope do not mean its safe. The 2nd, 3rd or 10th person could find a thin spot and trigger a large slab that propagates across an entire slope.
  4. Remotely triggering a slab from the ridge, sides or below is possible.
  5. Use safe travel protocols: One at a time in avalanche terrain, Stop in safe zones, Watch your partners and Avoid terrain traps.
  6. Assess the consequences if the slope slides. The larger the terrain = the larger the potential avalanche!

South of Turnagain - Johnson Pass/Summit Lake zone: Areas south of Turnagain Pass harbor a thinner, weaker snowpack with multiple weak layers present, including the MLK buried surface hoar. This area also received additional snow on Sunday and Monday and elevated Easterly winds. Similar to Turnagain Pass an avalanche triggered in this zones could propagate an entire slope and be large enough to bury or kill a person.

Remote triggered avalanche on Eddies occured yesterday afternoon after mulitiple people had skied the ridge.   

 


Avalanche Problem 2

Cornice

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

CORNICES: We had a report of a large cornice fall in upper Seattle Creek drainage over the weekend. Give cornices an extra wide berth as they often break farther back than expected.

LOOSE SNOW AVALANCHES (dry and wet): Daily warming and radiation from the sun could warm surface snow on steep Southerly aspects. Keep your eye’s out for roller balls or small wet-loose avalanches under rocks. On shaded aspects dry loose “sluff” is possible in steep terrain.

WIND SLABS: There is a lot of snow available for transport. Ridge top winds should remain light from the Southeast, but winds could puff up along some localized upper elevation zones. Should you see drifting snow, expect any recently wind loaded feature to be tender. Any wind transport will also be adding stress to a larger more dangerous avalanche problem, where triggering a small wind slab could step down into a deeper more dangerous layer.


Additional Concern

Glide Avalanches

Glide cracks are opening again. We know of one glide avalanche that has released recently in the Summit zone just north of Manitoba. Look out for glide cracks and limit exposure under them!


Mountain Weather

Yesterday: Thick valley fog was observed below 2000’. Above this elevation skies were partly cloudy. Temperatures remained around 30F near sea level and mid 20Fs near ridgetops. Ridgetop winds were light and variable. No new precipitation.

Today: Valley fog will continue through the morning and may burn off in some areas by the afternoon. Above the fog skies will be partly to mostly sunny. Daily warming will cause temps at sea level to increase from mid 20F’s to low-30Fs. Upper elevation temps will be in the mid to upper 20F’s. Ridgetop winds from the Southeast will range from 5-15mph with gusts in the low 20’s mph. No precipitation is expected.

Tomorrow: A similar day is in the forecast with partly sunny skies. Daily warming and mild temperatures in the mid to upper 20F’s is expected. Valley fog is possible. No new precipitation is expected and ridgetop winds should remain light.


*The Seattle Ridge anemometer (wind sensor) was destroyed. We have a replacement on the way and it should be operational by mid February.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 26  58 
Summit Lake (1400') 20  27 
Alyeska Mid (1700') 25  52 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 24  variable  12 
Seattle Ridge(2400') 26  *N/A   *N/A  *N/A  

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

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
© 2019 Chugach National Forest Avalanche Information Center. All rights reserved.
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