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Avalanche Advisory

Turnagain Area Avalanche Advisory
Saturday, April 7th 2018 5:43 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 is MODERATE at all elevations, but could increase to CONSIDERABLE in the afternoon with daily warming. Triggering a slab 1-2 feet thick is possible on all aspects, but could become more likely in the afternoon on Southerly aspects. If the sun breaks down a surface crust this afternoon natural wet-loose avalanches are also possible on Southerly aspects at all elevations. In addition, keep in mind there is still a chance for triggering a deeper avalanche 3-4+’ thick in older layers of the snowpack. 

Attention hikers and climbers in Portage Valley: Many popular hiking areas like Byron Glacier trail and even Portage Lake have avalanche terrain above them. Avoid being under large steep slopes where wet avalanche activity is possible in the afternoon and evening. 

For the Summit Lake Summary click HERE. 

 


 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.
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.
Avalanche Problem 1

Persistent Slabs

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It has been two days since a storm with strong wind ended and left behind 1-2 feet of snow across our region. Girdwood, Portage and the Northern side of Turnagain Pass received 18” - 24” and much less on the far Southern end of Turnagain Pass. Rapid warming from the sun, whumpfing, cracking and remote triggered avalanches have occurred over the last two days with most of the activity on Thursday. A handful of storm slabs have been triggered by skiers, boarders and snowmachiners on smaller terrain features in Turnagain Pass. The largest of these slabs released on Thursday on a SW aspect of Tincan late afternoon and may have been remotely triggered from the skin track 300+ feet away. Stability tests on a nearby slope revealed a reactive layer of facets above and below an old sun crust. This structure is present on many Southerly aspects (E - S - SW) and could be more reactive later in the day with warming. A new sun crust has formed on the surface, which is helping stability until it starts to melt today. On North to West aspects where the snow is drier, weak faceted snow sits below the new snow, and triggering a slab 1-2 feet thick will remain possible at any time of the day. Fast moving dry-loose “sluff” is also possible in steeper terrain in shaded areas.  

Overcast skies should become partly cloudy by late afternoon. This could be our warmest day of the year with temperature reaching the low-50F’s near sea level, mid-30F’s near ridgetops. It is important to pay close attention to how warm it gets and how wet the snow feels. Ease into terrain with a cautious mind-set and be ready to adjust your plans if you experience collapsing, shoot cracks, or see any avalanche activity.

An avalanche that released between 4pm and 5pm on Thursday on a SW aspect of Hippy Bowl on Tincan. Its unknown if this avalanche was natural or triggered remotely from the skin track. 

 

 Several snow pits on Thursday found propagation potential on facets associated with an old sun crust on Southerly aspects in two locations nearby the avalanche above. 


Avalanche Problem 2

Wet Loose

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SPRINGTIME WARMING: Dozens of small wet loose avalanches occurred on South and Southeast aspects in the afternoon on Thursday, just after the storm ended. Today a thin surface crust will require more energy to break down, but warmer air has already started to move into region and the sun should poke through the clouds by the afternoon. Sun and thin cloud cover can trap the heat and sometimes intensify the affects of solar heating. A thin crust has formed below 1000’ on all aspects and its also present on Southerly aspects (E - SW) at all elevations. If/when this crust softens and becomes moist, its time to avoid South aspects. Natural wet-loose avalanche activity will be possible near rocks and in steep terrain today.

Wet loose avalanches seen on Pete's North and Pete's South were visible Thursday evening. Although these point releases are small there is potential for a wet avalanche to trigger a 1-2' slab if the crusts become saturated.


Additional Concern

Deep Persistent Slabs

This new snow fell onto a snowpack with poor structure and several weak layers buried 2-4’ below the old surface. No avalanches have been reported on deeper layers of the snowpack. There remains some level uncertainty around the reactivity of these older weak layers, facets and buried surface hoar. Thin snowpack zones such as the Girdwood Valley and the South end of Turnagain Pass are more suspect for this structure, as well as some Northern and Easterly slopes with a generally thinner pack. Trigger points in this situation are often in thinner areas near rocks, but it is also possible to trigger this avalanche problem from areas along ridges. 


Mountain Weather

Yesterday was overcast with a few sprinkles of rain, but no measurable amounts were recorded.  Daytime temperatures were in mid-20F’s near ridgetops and upper-30F’s at sea level. Warmer air and cloud cover kept overnight temperatures in the mid-20F’s in the alpine and low-30F’s near sea level. Northeast winds were 5-15mph most of the day near ridgetops. 

Mostly cloudy skies are expected to become partly cloudy this afternoon. Today could be our warmest day of the year with lower elevation temperatures in the upper-40’s to low-50F and upper elevation temps reaching the mid-30F’s.  Overnight lows are expected to dip below freezing into the mid-20F’s. Northwest winds could range from calm to 10mph today. 

Sunday looks very similar with partly cloudy weather and warmer daytime temperatures. Low temps should dip below freezing at night. Winds are expected to be light and variable. Monday evening through Tuesday there’s a chance for rain and snow showers and moderate winds, but accumulation looks minimal at this point.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 31 82 
Summit Lake (1400') 34   0  0 34 
Alyeska Mid (1700') 31   79

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 24  NE  20 
Seattle Ridge(2400') 28  ESE  21 

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: Dec 01, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed
Placer River: ClosedClosed
Skookum Drainage: ClosedClosed
Turnagain Pass: ClosedClosed November 21 due to inadequate snow conditions. #hopeforsnow
Twentymile: ClosedClosed
Seward District
Carter Lake: ClosedClosed
Lost Lake Trail: ClosedClosed
Primrose Trail: ClosedClosed
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: ClosedClosed
South Fork Snow River Corridor: ClosedClosed
Summit Lake: ClosedClosed

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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
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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