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Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, February 9th, 2013 - 7:00AM
Expires
Sun, February 10th, 2013 - 7:00AM
Forecaster
John Fitzgerald
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.

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Sat, February 9th, 2013
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

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!”

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

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.

Weather
Sat, February 9th, 2013

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.

______________________________________________________________

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

______________________________________________________________

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Riding Areas
Updated Mon, October 26th, 2020

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

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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.