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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Graham Predeger  
Friday, February 27th 2015
Created: Feb 27th 5:49 am
2 Moderate Alpine / Above 2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
0 NO RATING Below Treeline / Below 1,000'
 Show the Complete North American Avalanche Danger Scale
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The Bottom Line

Above 2500’ the avalanche danger is MODERATE today where a poor snowpack structure will make it possible to trigger an avalanche 1-2’ deep.  Likely trigger points will be mid-slope on steep rollovers and unsupported convexities.  Steep, southerly aspects will also warrant special attention today as any localized, rapid solar warming could be enough to wake up a buried layer of facets.

 Below 2500’ the avalanche danger is LOW, where a supportable melt/ freeze crust has formed, locking up the shallow snowpack that does exist.


Primary Concern

Information from the field yesterday validates the fact that a poor structure (slab/ weak layer/ bed surface) is persisting and a fracture, if initiated has the potential to propagate across a slope.  The most reactive snow, and where you are more likely to trigger an avalanche appears to be in the mid-elevation band between 2400’ and 2900’.  This is where my partners and I experienced large and frequent collapsing yesterday; prompting us to change our travel plans and seek out mellower terrain.  Obvious red flags such as whumphing, recent avalanches and shooting cracks should not be taken lightly as this persistent weak layer is keeping us on the higher end of moderate danger right now.

Above 3,000’ our layer of concern is comprised of smaller, less advanced buried facets still overlain by a slab.  This is more difficult to see in a snowpit and whumphing and shooting cracks may not be so obvious until a slope avalanches, making safe travel protocol of the utmost importance.  Identify features of concern such as unsupported convexities and mid-slope roll overs.  Avoid these areas today or at the least expose only one person at a time and have a well thought out escape route and safe zone if a slope does slide.

A further concern on south facing slopes today has to do with direct sun and inverted (warmer at ridgetops) temperatures.  Rapid warming today could be enough to initiate an avalanche on steep, southerly terrain particularly near rock out crops or shallow spots in the slab as seen below.

Natural avalanche observed yesterday on the periphery of the advisory area near Grandview.  SSW aspect at about 4,000'.


Mountain Weather

Calm winds and clear skies prevailed in the backcountry yesterday with temperatures increasing to the low 30's at ridgetops by days end as high cirrus clouds moved in.  Winds are back online (light out of the west) at the Sunburst weather station after a successful anemometer replacement mission yesterday!

Temperatures are slightly inverted this morning with ridgetops readings in the low to mid-30's while Center ridge (1880') is reading 24 degrees at 6am.  Expect this air to mix and the inversion to lessen as the sun begins heating up the earth's surface.  Winds are expected to be in the 8-20mph range shifting to the southeast as clouds stream into our region this afternoon and evening.  

We may see a trace of snow overnight and up to a couple inches by tomorrow night but the upslope nature of this weak surface low looks to favor Anchorage more than the eastern Turnagain arm.

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 25 40 
Summit Lake (1400') 20 
Alyeska Mid (1700') 24  23 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 30  *W   *6  *14
Seattle Ridge(2400')  26 N/A   3  12

*Sunburst wind info is an average from 2pm to 6am.

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 11, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: OpenWide swaths of open river in the Placer Valley. Travel with extreme caution!
Skookum Drainage: ClosedSKOOKUM DRAINAGE CLOSED TO MOTORIZED USE ON APRIL 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: ClosedClosed for the remainder of the 2017 season.
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: Open
South Fork Snow River Corridor: Open
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
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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