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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, February 13th 2018 4:30 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

There is a CONSIDERABLE avalanche danger above 1000' due to recent snowfall and strong winds overnight. Human triggered avalanches remain likely. Fresh wind slabs up to 2 feet thick, should be expected on slopes with recent wind loading. Additionally, weak layers deeper in the snowpack may be triggered, creating a much larger avalanche.

Below 1,000' the danger is MODERATE.


 Show the Complete North American Avalanche Danger Scale
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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

Coming up this Friday night, Feb 16th - The 2018 SNOWBALL!! Join the CNFAIC, our non-Profit Friends group and Alaska Avalanche School for live music by the Hope Social Club, silent auction, raffle, locally brewed beer and good people. This benefit supports avalanche safety in Southcentral Alaska, we look forward to seeing you there!!

Coming up Saturday, Feb 17th, from 11am-1230pm - Free Avalanche Beacon Practice with CNFAIC! We will be hosting a short workshop on how to effectively perform a companion rescuce. Open to all users and all levels; swing by on your way to the hills if your are just getting into avalanche safety or simply need a refresher!

 


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Yesterday saw continued snowfall adding a couple more inches of new snow. Rain/snow line fluctuated from 200'-500'.  Overnight winds shifted to the north and gusted into the 60s on Seattle Ridge. The storm total of 6-12" of snow fell on weak surface snow and/or added load to slopes harboring buried weak layers. We have been talking about the buried January 21st surface hoar needing more of a slab to be reactive and produce large avalanches. The storm snow combined with wind has likely created that slab. We do not yet have enough information about how the snowpack will behave after this loading event. Small avalanches at the old snow/new snow interface could 'step down' and release a much larger and unmanageable slide. Don't let the sunshine blur your judgment. Today is a day to be extra cautious and evaluate the snowpack carefully. Look for recent avalanches, shooting cracks and listen for 'whumpfs'. 

Crown profile from Twin Peaks shows the January 21st buried surface hoar layer that may now be reactive with added load. 

This avalanche in the North Cornbiscuit Chutes occurred Sunday on recently buried surface hoar and the cracking in the bed surface is believed to be on the January 21st buried surface hoar layer. This illustrates the potential for failure on more than one weak layer.  Photo: Mike Records


Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Moderate to strong winds coupled with 6-12" of new snow have likely formed wind slabs 1-2' thick. Because these slabs are likely sitting on weak old snow, they are expected to be quite sensitive and easy to trigger. The winds shifted from south to north last night so multiple aspects may be loaded. It will be important to pay attention to where the snow feels stiff, looks pillowed or sounds hollow and watch for shooting cracks. 

Cornices: Cornices are unpredictable and can break further back along a ridge than expected. Give these features plenty of space.

Loose snow sluffs: Sluffs on steep slopes are likely with the recent new snow. Warm temperatures and sun hitting steep southerly slopes may also trigger roller balls that may progress to natural loose snow avalanches as they entrain surface snow. 

 


Additional Concern

Deep Persistent Slabs

The recent snowfall is a relatively small load on top of our generally weak snowpack structure in the Alpine (above 3,000'). However, even a small load combined with strong winds and warming temperatures could help tip the balance. Someone might be able to trigger a large deep slab that breaks in the bottom half of the snowpack. It's good to remember that multiple layers of old buried surface hoar, facets and crusts exist deep in the pack and near the ground. Small incremental loading can sometimes be just enough to 'wake up' dormant deep layers. The overall poor structure is worth keeping in mind, as outliers can happen like last week's Twin Peaks slide.

 


Mountain Weather

Yesterday skies were obscured and light snow/rain fell throughout the day depending on elevation. Temperatures were in the 30Fs at sea level and 20s at upper elevations. Winds started out southerly and shifted to the north last night. Winds overnight were NW 20-30 mph gusting into the 60s. 

Today will be mostly clear and sunny with some valley fog. Temperatures will range from the 30Fs to the 20Fs as you go up in elevation. Winds will remain elevated from the north this morning with gusting into the 40s but should calm down this afternoon. Temperatures cool into the teens overnight.

Tomorrow is forecast to be partly cloudy with a slight chance of snow and then clearing again on Thursday. There is another chance for snow over the weekend. Stay tuned! 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  33 0.1  67 
Summit Lake (1400')  28 0.1  26 
Alyeska Mid (1700')  30  2.8 0.19  59 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 20  NE-NW   12 37
Seattle Ridge(2400') 25  SE-NNW   22 66 

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, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: ClosedClosed as of 4/27
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

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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