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Avalanche Advisory

Turnagain Area Avalanche Advisory
Monday, January 15th 2018 5:30 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

A CONSIDERABLE avalanche danger remains at elevations above 1,500' in the Turnagain Pass area. Triggering a large slab avalanche was likely yesterday and trending toward possible today. However, it is only the 2nd day after a storm and these slabs are 2-5+' thick and unmanageable. Today is a day to follow the 'travel advice' for CONSIDERABLE danger: Careful snowpack evaluation, cautious route-finding and conservative decision making. A LOW avalanche danger exists below 1,500' where triggering an avalanche is unlikely.


 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.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Storm slabs, wind slabs and cornice falls associated with the heavy snowfall two days ago are still an issue today. Although the bonding of the new snow to the old snow surface is occurring quickly, slabs and cornices may still be triggered. Yesterday there were three large avalanches seen/reported in the Turnagain Pass zone. Two of these were in Main Bowl of Seattle Creek and were storm slabs triggered by snowmachiners. One was triggered by a cornice fall and one was remotely triggered from above. The third avalanche was on the SE face of Seattle Ridge and is unknown if this was a natural slide or triggered remotely from a snowmachiner(s) on the ridge. An avalanche course heard the slide from across the valley. This third avalanche looks to have stepped down into deeper weak layers in the pack. See photos below.

For today, if visibility allows for travel to the upper elevations, know that these types of avalanches remain possible. Furthermore, cornices have grown and could break farther back than expected. It is only the 2nd day out of a storm and don't expect all slopes to remain intact. Although triggering a storm slab or wind slab avalanche will be less likely today, these slides can be large and have high consequences. Quick hand pits and getting your shovel out to look at the new/old snow bonding is a good way to help assess the slopes you are interested in riding. Assessing deeper weak layers in the pack is more difficult - more on that below. Keeping with safe travel habits, chiefly exposing only one person at time if venturing into avalanche terrain is key. Watch your buddies closely. 

 


Close up of the crown of avalanche above, note the dark bed surface, this avalanche 'stepped down' into weak snow near the ground

 

Yesterday a snowmachine triggered a cornice fall, which triggered this storm slab avalanche in Main Bowl (1st Bowl) in the Seattle Creek drainage. 


Avalanche Problem 2

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering a deep persistent slab is just as concerning, if not more concerning, as the avalanche issues in the new snow. This is because these can be larger and more destructive avalanches. Underneath the storm snow sit a variety of weak layers deeper in the snowpack. The first is the New Year's buried surface hoar that is anywhere from 30" to ~5' deep (general snow depths vary widely due to wind distribution and snowfall differences). This layer was showing signs of being reactive in pits yesterday - it took a bit of force to fail, but once it fails, it's sliding easily. There are also facets that have been found near crusts in the mid to lower pack as well as basal facets that sit near the ground. The point is, this is a complicated snowpack that just received a lot of weight - avalanches triggered deeper in the pack can be very large and unsurvivable.

 

Video of failure in the New Year's buried surface hoar on Sunburst ridge, while the storm snow has bonded well in this area


Mountain Weather

Partly sunny skies filled the area yesterday with no precipitation. Ridgetop winds bumped up to the 30's with gusts in the 50's mph yesterday morning from the East before tapering off significantly in the afternoon and overnight have been light and variable. Temperatures remained warm, in the mid to upper 20'sF along ridgetops and in the mid 30'sF below 1,000'. A slight inversion is in place this morning with valley bottoms in the upper 20'sF. 

Today, we are just on the edge of some instability showers to our Northeast. We may see partly clear skies with no precipitation, yet we may also see these showers back down our way to bring 1-2" of snow above 1,500 and light rain (.2") below this. Ridgetop winds are expected to be relatively light, 5-15mph from the East today and into tonight. Temperatures will stay on the warm side with mid 30'sF at 1,000' and the upper 20'sF along the ridgelines.

Early tomorrow another warm storm system moves in from the East. As of now, the rain/snow line looks to be around 2,000' and possibly higher. Models are showing precipitation amounts in the 1-2" of rain and 1-2+ feet of snow up high by Wednesday night. Stay tuned and cross your fingers for a lower rain line.

*A big THANKS to the folks who cleared off the Seattle Ridge weather station yesterday! 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 31  60 
Summit Lake (1400') 28  15 
Alyeska Mid (1700') 33  trace  0.04  48 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 27   NE 21  55 
Seattle Ridge(2400') 29  SE  15  30 

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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