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Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, December 14th, 2014 - 7:00AM
Expires
Mon, December 15th, 2014 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is expected to rise to HIGH  later today at elevations above 2,500′ where 10-16″ of new snow with strong winds are forecast. Natural slab avalanches 1-2′ thick, or more, are likely to occur and human triggered avalanches are very likely. In areas receiving less snow the danger will be CONSIDERABLE.  Avoiding all avalanche terrain is recommended for today and into tomorrow as this storm system moves through.

At elevations from 1,000′ to 2,500′ a  CONSIDERABLE  avalanche danger is expected where avalanches releasing from above have potential to run into this mid-elevation band. At these mid-elevations, we may also see some natural wet avalanches on step slopes where wet snow will accumulate.  

Below 1,000, there is no snow and no danger rating. However, steering clear of the bottom of avalanche path runout zones where debris from above could funnel into this snow free zone is advised. For example, avoiding hiking along trails in the Portage Valley.

Today looks to be a good day for Christmas shopping.

——————————————————————–

The next advisory will be Tuesday Dec16th at 7am.

Avalanche Outlook for Monday: The avalanche danger is expected to remain HIGH above treeline in areas seeing over a foot of snow today and CONSIDERABLE at treeline. Sunday night through Monday evening an additional 10-16″ of snow is forecast to fall above 1,500 with ~1.5″ of rain below 1,500′.

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Sun, December 14th, 2014
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
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
No Rating (0)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

A warm and very intense storm is arriving as we speak. The rain/snow line should rise to 2,000′ and 10-16″ of snow is forecast above 2,500′. Associated with the new snow will be very strong Easterly ridgetop winds. This is a classic storm snow avalanche problem. With wind likely to affect most locations above 2,500′, naturally occurring wind slab avalanches are expected on many leeward slopes. These are expected to run into the 2,000′ elevation zone, where it may be raining, and possibly further.

Not only is a foot or more of new snow falling in 12 hours, accompanied by strong winds, a concern in itself, it is falling on a very weak pre-existing surface. Widespread surface hoar up to the ridgetops – 2cm (3/4″) in size, which is significant – was just starting to be covered up intact and upright yesterday. Hence, bonding between the new snow and old snow will be poor with this persistent weak layer sandwiched in between. As snow piles up and becomes cohesive with the warm temperatures, slabs will have potential for wide propagation.

Slab depths for today’s expected new snow will be in the 1-2′ range. These are not exceedingly thick slabs for a HIGH danger day, but the expected rapid loading on a weak layer of surface hoar should produce widespread avalanche activity with dense debris. Steering clear of avalanche terrain while it continues to snow and blow is recommended.

Avalanche Problem 2
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

Rain on an old battered and frozen snowpack is expected from ~2,000′ and below. Above this, around 2,500′, 6-8″ of wet snow is likely to fall on a stout and well developed crust. Naturally occurring wet loose avalanches composed of the new wet snow are likely to run on steep slopes. Areas that are in this zone are the East face of Seattle Ridge and Magnum’s West face.

Weather
Sun, December 14th, 2014

Yesterday, skies were mostly cloudy with light snow beginning to fall in the early afternoon as the leading edge of today’s low pressure system pushed in. The rain/snow line rose to 500′ by the evening. Don’t forget about the table below for additional past 24-hour weather details!

Overnight we have seen ~.3-.5 of rain below ~1000 in the Girdwood Valley and Portage area with 4″ of wet snow at the Center Ridge (Turnagain Pass) SNOTEL site at 1880′. Ridgetop Easterly winds are on the rise from the teens to the 30’smph with gusts to the 50’s. Temperatures are steadily climbing (unfortunately) with 1,000′ temperatures in the mid 30’sF.

Today, we will see temperatures rise another few degrees F with the rain/snow line creeping to 2,000′. Between 1 and 1.5″ of water equivalent is expected by this evening at Turnagain Pass with 10-15″ of snow at the above treeline elevations. Ridgetop Easterly winds are forecast to be in the 30-40mph range with stronger gusts.

Monday, precipitation, Easterly wind and even temperature should decrease slightly. Models are showing 1 – 1.5″ of rain below 1,500′ and another 10-16″ of snow above.

A series of low pressure systems will continue to move through the Northern Gulf with additional cooler temperatures and additional snow (hopefully to sea level). Stay tuned.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31   4   0.4   22  
Summit Lake (1400′) 28   0   0   4
Alyeska Mid (1700′) 32   2   0.6   15  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25    E 21   54  
Seattle Ridge (2400′) 27    SE 15   31  
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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

Area Status Weather & Riding Conditions
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Johnson Pass
Closed
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Skookum Drainage
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Turnagain Pass
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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.