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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, January 19th 2018 5:24 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

CONSIDERABLE avalanche danger remains at elevations above 2,500' in the Turnagain Pass area. Triggering an isolated storm slab or a very large Deep Slab avalanche (3-8+ feet) is trending towards possible today. However, it is only the 2nd day after a storm and a lot of uncertainty exists about how the snowpack is adjusting to its new load. Today is a day to follow the 'travel advice' for CONSIDERABLE danger: Careful snowpack evaluation, cautious route-finding and conservative decision making.

Below 2500, treeline, the avalanche danger is MODERATE where a crust is helping to stabilize the snowpack, but an avalanche from above could run into this zone. There is LOW avalanche danger below treeline where very little snow exists.

**Heightened avalanche conditions exist in the Summit Lake zone. Click HERE for recent observations. 


 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.
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.
Avalanche Problem 1

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Several storms this week brought 3-6+’ of snow to the upper elevations and ended on Wednesday. This last storm caused a widespread avalanche cycle including: a very large D3 avalanche on the SW face of Sunburst, and dozens of large wet avalanches in the mid elevations. Above freezing temps were noted in the alpine during this cycle and rain may have reached ~3000’ at some point, but this has not been confirmed with field data. What we do know is this wet snow has frozen into a solid stable crust below 2500’, but in the alpine this moist snow layer gradually goes away and is not obvious due to new snow covering it up. Basically there is an invisible gray line between Treeline and the Alpine where we go from a stable snowpack to a Deep Persistent Slab problem, where several weak layers (buried surface hoar and facets) are sitting below 3-8+ feet of snow. This avalanche problem comes with a lot of uncertainty due to how deeply buried these layers are. It will be impossible to know where the thinner areas of the snowpack are - likely trigger spots. A snowmachine or a person may get away with riding on steeper slopes, but if a thinner area is found, the consequences could be unsurvivable if caught. This is no beast to mess around with. Keeping your terrain choices conservative in the Alpine will be key. This means choosing low consequence terrain and avoiding large steep slopes.

 Keep in mind:

  1. Obvious signs of instability like cracking or collapsing “whumpfing” may not be present until it’s too late
  2. Be aware of people above and below you, an avalanche from above could run into the treeline elevation band
  3. Several tracks could be on a slope before someone finds a trigger spot
  4. Remote triggering from above, below or adjacent to a steep slope is possible from a thinner area of the snowpack
  5. Snow pits and stability tests may not be representative due to how deeply buried these weak layers are

 

Yesterday we investigated the avalanche on Sunburst and found the New Year's buried surface hoar to be the most likely culprit. This avalanche wraps around the West Ridge near the skin track all the way to the gully below the weather station (~3/4 mile) and filled Taylor Creek up with debris. 

 

 

Debris in Taylor Creek

 

 

Snow pit at 3300' just above the crown on a W aspect of Sunburst. 


Avalanche Problem 2

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering a storm slab in the top 1-3’ of snow is becoming less likely as we move away from the storm that ended Wednesday. Cold temps and benign weather is helping stabilize any mid-storm weaknesses within the new snow. Storm slabs may be lingering in the alpine, above 2500’, on steep to very steep terrain. This is an additional reason to avoid larger terrain and stay off of slopes steeper than 35 degrees. 


Additional Concern

Cornice

Cornices have been growing over the last week and could be easy to trigger. Give these features a lot of space and remember they can break further back from a ridge than expected.  A cornice fall also has the potential to trigger a very large avalanche on the slope below.


Mountain Weather

Yesterday skies were clear becoming partly cloudy in the afternoon. Temperatures were between 20-25F and winds were calm. No precipitation was recorded. 

Today skies will be overcast and valley fog and low lying clouds are also possible. Temperatures will be in the mid to low 20F’s and may drop into the teens overnight. Ridge top winds are expected to remain light and variable. 

Benign weather is expected tomorrow through the weekend with mostly overcast skies and a possibility of snow flurries.  Temperatures will be in the teens to low 20F’s and winds are expected to remain light through the weekend. 

**Seattle Ridge weather station stopped recording wind data 1/17/18 rime covering the anemometer.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 23 56 
Summit Lake (1400') 17 15 
Alyeska Mid (1700') 26   43

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 20  variable  16 
Seattle Ridge(2400') 23   *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: 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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