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Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, December 16th, 2014 - 7:00AM
Expires
Wed, December 17th, 2014 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

A HIGH avalanche danger continues in the backcountry at elevations above 2,500′. Storm snow slab avalanches 2-5′ in depth have the potential to release naturally and human triggered avalanches are very likely. These have the potential to run into the treeline elevation band between 1,000′ and 2,500′ where a CONSIDERABLE avalanche danger exists. Additionally, wet avalanches are possible at the mid-elevations on steep slopes over 40 degrees. Travel in avalanche terrain (slopes over 35 degrees with nothing steeper above you) is not recommended.

It is game on in the backcountry. Although there is no snow at the road elevations, there is plenty of snow at the higher elevations. This week marks the first time this season we have a documented persistent weak layer in the snowpack. When this storm cycle finishes, skies clear and folks start getting out – have your hackles up!  This set up, described below,  has lead to accidents in the past  and we need to be patient, let the new snow settle and prove itself NOT guilty before getting on slopes over 35 degrees.

——————————————————————–

The next advisory will be Thursday Dec18th at 7am.

Avalanche Outlook for Wednesday: With decreasing temperatures and precipitation, the avalanche danger is expected to drop to CONSIDERABLE  at elevations above 2,500′ and to MODERATE below 2,500′. A decline in natural avalanche activity is expected, however  human triggered large avalanches 2-5′ deep will remain likely above 2,500′.  

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Tue, December 16th, 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

As of this morning, the storm rages on. Although it is raining below 1,500′, it is snowing and blowing at the upper elevations. Storm totals in these upper elevation areas have been variable: from only a few inches in the Summit Lake area to ~2′ on Turnagain Pass and 4′ or more in the Girdwood and Portage Valleys. These numbers are for ~3,000′ and above and are estimated from the amount of rain/wet snow reported from weather stations at lower elevations (see those water numbers in the Mountain Weather section). Along with the snow, ridgetop winds have been strong and sustained from the East. Considering this, slab depths for avalanche activity are variable, 2-5′ or more.

The primary concern for today and into the remaining part of the week will be how the new snow is bonding with the pre-existing surface. We have been talking a lot about a widespread layer of surface hoar that extended to the ridgetops before being buried under the current storm snow. This set up has the potential for inducing widespread avalanche activity. See video from yesterday. Unfortunately, with little to no visibility there is a good deal of uncertainty as to how the new snow has been acting. Along with this, our field days since the storm began have only allowed us to see what is going on from mid-mountain elevations and below.

All that said, the message is simple: Several feet of new snow combined with wind falling on a weak layer with a slick bed surface below requires a conservative mind set.

Below is the snowpack from a slightly scoured area on the Sunburst ridge yesterday. At 2,700′ the snow changed character significantly from wet to dry and the avalanche potential increased rapidly. This points to increasing danger with elevation. The nature of this weak layer can allow for wide propagation and triggering avalanches remotely, including from below.

 

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

Although it has been raining from ~1,700′ and below with wet snow falling up to ~2,500′, we have seen little wet avalanche activity. The rain has wiped out the snow cover below 1,500′, but in the elevation band from 1,500-2,500′ the snowpack goes from 0-2′. The main concern for wet avalanches is the new heavy snow (10-12″) sliding on the old hard surface underneath. I was able to trigger a push-a-lanche yesterday on a slope ~40deg. Avoiding steep slopes at these wet snow elevations, including runout zones from steep slopes above you, is recommended as this wet storm continues.

As we go into Wednesday, temperatures are forecast to cool. If this is the case, the mid-elevations will begin to freeze and wet avalanche potential will decline. 

Weather
Tue, December 16th, 2014

Beginning Saturday afternoon, we have seen several fronts and embedded low pressure systems move through the Eastern Turnagain Arm zone. Precipitation totals from the start of this event are below with the past 24 hour data in the tables. During this cycle the rain/snow line has fluctuated between 1,500′ and 2,500′ (higher in some locations). Easterly ridgetop winds have remained strong, averaging 25-40mph.

Storm totals in water equivalent (Saturday afternoon – Tuesday morning):
Turnagain Pass:  2-2.5″ H20
Girdwood Valley:  ~4″ H20
Summit:  Only ~.5″ H20

For later today, the storm looks to begin to cool off and slow down. We should see another .5″ of precipitation, 4-6″ of snow above 1,500′ (possibly more). Ridgetop winds will remain strong in the 20-30mph range from the East. Temperatures at 1,000′ look to fall from ~35F to 30F, with a rain/snow line decreasing to ~1,000′.

For Wednesday, continued light precipitation with falling temperatures is forecast. Models are showing ~.5″ of precip this evening through Wednesday evening with a rain/snow line dropping to 500′. Thursday we may see clearing skies before another warm system looks to move in.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33   5+   1.2   30  
Summit Lake (1400′) 34   0   0.3   4  
Alyeska Mid (1700′) 35   0.5   2   14  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 27   E   27   54  
Seattle Ridge (2400′) 29   N/A   N/A   N/A  
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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
Glacier District
Johnson Pass
Closed
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
Closed
Resurrection Pass Trail
Closed
Snug Harbor
Closed
South Fork Snow River Corridor
Closed
Summit Lake
Closed

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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.