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Avalanche Advisory

Turnagain Area Avalanche Advisory
Monday, January 28th 2019 7:00 am by Graham Predeger
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

There remains a CONSIDERABLE avalanche danger above treeline throughout Turnagain Pass.  Forecasters and observers continue to find a layer of surface hoar buried last week (MLK day) that was responsible for several human-triggered avalanches on Saturday.  Given the nature of this problem, avalanches have the potential to be triggered from significant distances away from a slope and may be quite wide and connected. 

If winds kick up from the East today, fresh wind slabs may add an additional stress onto this known weak layer.  Cautious route finding and conservative decision-making will be essential for a safe day of mountain travel. 

SUMMIT LAKE / JOHNSON PASS:  Dangerous avalanche conditions exist in these regions south of Turnagain Pass. Strong wind, a poor snowpack structure and recent avalanche activity all point to an unstable snowpack.


 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.
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Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

It doesn’t take much digging right now to find and easily identify the buried layer of surface hoar (buried on MLK day) responsible for a number of human-triggered avalanches on the motorized side of Turnagain Pass on Saturday.  We found this same layer to be widespread on Sunburst yesterday above 2,000’ (and up to our high point at 3,400’).  It shows up in a snowpit wall or snowmachine trench as a thin grey line 12-24” below the surface on all aspects.  Though no obvious red flags were present during yesterday’s tour, the poor structure and widespread nature of this persistent weak layer has our hackles up.  Thin spots in the slab (near rocks or wind scoured areas) are more likely trigger points and should be avoided. 

 There is no mistaking the MLK buried surface hoar layer in snowpits right now.  As seen on Sunburst yesterday buried 12-16" below the surface.

Snowpack tests over the last two days have all showed high propagation potential on the MLK layer.  With such a connected weak layer across multiple aspects and elevation bands, any avalanche initiated has the potential to be quite wide.  As seen on Saturday, these avalanches can be triggered remotely from the bottom of a slope or even an adjacent ridge. 

Maintain your situational awareness of where you are on slope in relation to avalanche terrain, any objective hazards (terrain traps) and other groups today.  This is the type of avalanche problem that can very quickly affect an adjacent, unsuspecting party.  Cautious route-finding and conservative decision-making is critical when dealing with known persistent weak layers.

Long shooting crack and subsequent cornice fall triggered by snowmachiners on the ridge near the Seattle Ridge weather station on Saturday Jan.26th.  photo: Iron.iii.Oxide

Wind slabs: If forecasted winds kick up in the 20-40mph range from the east today, expect fresh wind slabs to form on lee aspects. This additional weight will push the MLK layer closer to its tipping point.

Cornices: Give these backcountry bombs a wide berth while traversing ridges and limit exposure underneath.  A cornice fall today on a slope greater than 30 degrees may trigger a slab avalanche below. 

South of Turnagain - Johnson Pass/Summit Lake zone: Areas south of Turnagain Pass generally harbor a thinner, weaker snowpack with multiple weak layers present, including the MLK buried surface hoar layer.  An avalanche triggered in these zones could step down into deeper weak layers, with the potential for large avalanches.  See video here  of two separate and reactive weak layers in a January 26th snowpit in the Silvertip area south of Turnagain Pass, that clearly demonstrates the step down potential. 


Mountain Weather

Yesterday:  Mostly cloudy skies and flat light dominated the eastern Turnagain arm region.  Ridgetop winds were light from the east with the occasional gust into the 30’s with no measurable precipitation.  Temperatures were consistent in the low 20’s at ridgetops (Sunburst at 3880’) and mid to high 30’s at sea level (Portage).

Today: East winds are expected to bump up into the 20-40mph range as a low moves up Cook Inlet.  We may squeeze out 2-5" of snow under overcast skies with a rain/ snow line around 500'.  Temperatures look to be in the mid-30's at 1,000' and mid-20's at ridgetops.

Tomorrow: Tonight and into tomorrow unsettled weather continues.  Precipitation type and rain/ snow line will be the big question.  Generally though, temperatures look to be cooling throughout the work week as the unsettled pattern continues.  Think #snowtosealevel

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed.  We are currently working to replace it. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 32   0 58 
Summit Lake (1400') 28   0 20 
Alyeska Mid (1700') 32  trace  .01  44 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  ENE  13  44 
Seattle Ridge(2400') 27  *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

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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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