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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, April 6th 2018 5:33 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 will remain at CONSIDERABLE on all aspects above 1000’. Triggering a storm slab 2 feet thick is likely on shaded aspects and will become more likely in the afternoon on Southerly aspects with daily warming. In addition, keep in mind there is still a chance for triggering a deeper avalanche 3-4+’ thick in older layers of the snowpack. 

Below 1000’ the avalanche danger is MODERATE where a superficial crust has formed. If the sun comes out today natural wet-loose avalanches are possible on Southerly aspects at all elevations.


 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

SKOOKUM VALLEY drainage remains closed to snowmachines for the remainder of the season as per the Chugach National Forest Plan.  Please stay to the West of the railroad tracks until you are South of Leubner Lake.


Avalanche Problem 1

Storm Slabs

Almost Certain
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Unlikely

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A storm that ended yesterday morning left 1-2 feet of new snow across our region favoring Girdwood, Portage and the Northern side of Turnagain Pass. Several human triggered avalanches occurred on Tincan yesterday on the new/old snow interface. The most notable was a large avalanche in Hippy Bowl that released late in the afternoon on a Southwest aspect. As of now its unknown if this avalanche was natural or triggered remotely from 300+’ away. Earlier in the day observers found easy propagation on facets associated with an old sun crust on a similar aspects and elevation. Prior to this storm surface conditions were variable and consisted of melt/freeze crusts and patches of near surface facets. At this time we do not know how widespread this particular facet/crust combo is across any given slope or how long it will remain reactive. We do know that whumpfing, cracking and recent avalanches were all observed yesterday - and these are signs the snowpack needs more time to adjust. As this new snow settles and becomes more cohesive the size of a slab can increase a day or two following a storm. Today as temperatures increase in the afternoon the likelihood for triggering a larger slab will increase on Southerly aspects later in the day. On shaded aspects with dry loose snow, triggering a slab is likely at any time during the day on slopes steeper than 35 degrees.

An avalanche in Hippy Bowl on a SE aspect of Tincan occured early in the evening and its unknown if it was natural or remotely triggered from the ridge. Earlier in the day observers dug several pits and found some propagation potential on the new/old snow interface, but tests results varied in nearby locations. See video below and click HERE for details about stability tests in these locations. 

 

Small remote triggered avalanche on NW aspect on Tincay in an area where the snow remained dry all day. Note the large shooting cracks nearby. 


Avalanche Problem 2

Wet Loose

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SPRINGTIME WARMING: Yesterday dozens of small wet loose avalanches occurred on South and Southeast aspects in the afternoon. This is very common in the spring on the first day of sun following a storm. Today a thin surface crust has formed on South aspects and it will take more energy to break down this crust. Warmer air has already started to move into the upper elevations and daytime highs could upper 40F’s near sea level. Pay attention to surface warming as daily temperatures will rise above freezing in the afternoon with possiblity of light rain showers. Thin cloud cover can trap the heat and sometimes intensify the affects of solar heating. A superficial crust has formed below 1000’ on all aspects and if this crust softens wet-loose avalanche activity is possible near rocks and in steep terrain. 

Loose snow avalanche triggered by sun and warming on SE aspect of Seattle Ridge in the afternoon yesterday. 

Other avalanche issues to keep in mind: 

Cornices: Daily warming and sunnier weather can make cornices more unstable. As always give cornices plenty of space and limit exposure underneath them.

Dry loose:  Dry loose “sluffing” was triggered on steep shaded terrain features yesterday. Today a fast moving ‘sluff’ could knock you over on larger slopes harboring loose dry snow. 


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. So far there were no avalanches reported on deeper layers of the snowpack. There remains some level uncertainty around the reactivity of these older weak layers from mid winter (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 a storm ended in the morning with little to no precipitation recorded after 6am. Skies became clear and sunny by mid afternoon. Strong Easterly wind decreased to 5-15mph from the East by late morning. Daytime high temperatures at sea level were in the mid 40F’s and mid 30F’s at 1800’ and remained in the low 20F’s near ridge tops. Overnight temps dropped into the mid to low 20F’s at all elevations.  

This morning skis will be clear and may range from partly cloudy to overcast in the afternoon. A few scattered rain/snow showers are possible in the afternoon, but no notable accumulation is expected. Warmer air associated with a surface low is expected to move into our region today and tomorrow. Daytime high temps at sea level may reach the mid to upper 40F’s and mid to upper 30F’s near ridge tops. Overnight temps should drop back into the mid to upper 20F’s. Winds will be light and variable.

Daytime temperatures on Saturday may be the warmest we’ve seen this year with a possibility of temps in the 50F’s at sea level. Overnight lows are still expected to dip below freezing into the mid 20F’s. Skies could range from cloudy to partly sunny both on Saturday and Sunday. Winds are expected to remain light and variable through the weekend. 

*The last strong gust occured at 7am on Sunburst near the end of the storm that ended yesterday morning. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 30  83 
Summit Lake (1400') 24  36 
Alyeska Mid (1700') 30   .02 81 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 21  ENE  11  *42 
Seattle Ridge(2400') 25  SE  25 

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: Apr 20, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: Open
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: Open
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: Open
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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