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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   John Fitzgerald  
Saturday, February 9th 2013
Created: Feb 9th 5:30 am
4 High Alpine / Above 2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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The Bottom Line

The avalanche hazard above treeline will rise to HIGH during the day as high winds and new snow create wind slabs that will be easy to trigger.  Natural avalanches are likely and human triggered avalanches are very likely above treeline.  Below treeline and in sheltered areas the hazard will rise from MODERATE to CONSIDERABLE where new storm snow will slide easily on a slick and hard crust.  The general trend is for an increase in hazard through the day.  Travel above treeline and in wind affected areas is not recommended today.


Primary Concern

Wind Slab

The winds have begun cranking up into the 60 mph range this morning at ridgetops.  Light density snow that fell two days ago combined with new snow will get blown around to form sensitive wind slabs today.  Yesterday multiple parties reported seeing good bonding between the newest storm snow/wind slab and the old snow surfaces.  The reactivity of the surface snow will increase today and will be most easily triggered as new slabs are forming.  With potentially very rapid loading occurring today (50+ mph winds and up to 12" of new snow forecasted), these slabs will be very sensitive to human triggers. 

A general lack of persistent weak layers in the upper snowpack will focus my attention on the interface between yesterday's snow surface and today's new snow. The exception to this are very isolated pockets of surface hoar that were observed on Tuesday.  With high winds expect loading to occur further downslope than normal as well as in the lower elevations.  

Storm Snow

Below treeline an additional 6-8" of new snow on its way will build slabs on a slick and hard crust that will be easy to trigger.  While these storm snow slabs will be smaller than new wind slabs they are worth looking out for today.   Watch for these slabs to be most easily triggered on steep rollovers in the lower elevations.

Be on the lookout for the most obvious signs of unstable snow: avalanches, shooting cracks and "whoompfing"/collapsing.  If and when you are seeing these signs this is nature screaming in your ear, "Hey, it's time to back off and turn around!"


Secondary Concern

The deep slab problem has not shown itself in the form of an avalanche in almost a month.  While this lack of activity is an encouraging sign, there is still weak snow at the base of the snowpack, primarily above 2,000' in elevation.  While the chance is remote for a deep slab avalanche to occur today, it is still worth remembering what is deep down in the snowpack.  Relatively smaller avalanches initiated in the upper snowpack have the potential to step down in older layers of snow near the ground.  This problem has a greater potential to show itself in areas of more shallow snow as evidenced here.


Mountain Weather

A generally calm day in the mountains yesterday has given way to increasingly high winds this morning as a large and well organized low pressure center moves towards the region.  Snow has begun to fall and ridgetop temps are currently in 20s F.

The NWS has issued the following warning:

...HIGH WIND WARNING REMAINS IN EFFECT UNTIL 4 PM AKST THIS
AFTERNOON FOR PORTAGE VALLEY AND TURNAGAIN ARM...

* LOCATION...PORTAGE VALLEY AND TURNAGAIN ARM.

* WIND...SOUTHEAST 45 TO 65 MPH WITH GUSTS TO 85 MPH.

* TIMING...STRONG WINDS WILL CONTINUE THROUGH EARLY THIS
  AFTERNOON. WINDS WILL BEGIN TO DIMINISH LATE THIS AFTERNOON.

Wind will be the major player in creating dangerous avalanche conditions in the mountains today.  New snow will play a close second in this equation.   Snow fall amounts should be in the 6-12" range and temps at 1,000' will be in the low 30s F

Winds should back off slightly by this evening and snowfall should continue overnight and into Sunday.

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Wendy will issue the next advisory tomorrow morning February 10th.

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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 08, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedRain and snow have fallen in Turnagain Pass this week, but not enough to open for snowmachining. Continue to check back to this site for updates.
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail is expected to open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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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.


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