Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, December 23rd, 2016 - 7:00AM
Expires
Sat, December 24th, 2016 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

A generally LOW avalanche danger exists in the mountains surrounding Turnagain Pass. The surface snow is very loose and triggering loose snow avalanches (sluffing) on steeper slopes should be expected. Triggering a slab avalanche in ‘Green light’ conditions is still possible. This includes, fresh shallow wind slabs where the winds may be blowing just enough to move snow and old/stiff wind slabs found in very steep rocky terrain.

*The snowpack in the Summit Lake area on the Kenai may be more unstable as whumpfing was reported above 3,000′ yesterday. Recent observations HERE. We have little information from the Girdwood Valley and unstable snow could be found in this area as well.

CHRISTMAS WEEKEND OUTLOOK:
Expect avalanche danger to rise with new snow and wind that is forecast for Christmas!

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Fri, December 23rd, 2016
Alpine
Above 2,500'
Low (1)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Low (1)
Treeline
1,000'-2,500'
Avalanche risk
Low (1)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

One more sunny day is on tap (24 seconds more than yesterday) before clouds fill in tomorrow and we wait in anticipation for how the ‘Christmas Storm’ develops. The winds that were forecast yesterday did not produce at Turnagain, leaving the majority of the snowpack capped with 6-12+” of very soft and loose faceting snow. This has made for good riding conditions, but it has also created a ‘base-less’ pack in thin areas and early season hazards such as rocks still remain.

Fresh shallow wind slabs:  We are missing data from two of our key wind sensors from last night. Winds may have picked up just enough to form shallow wind slabs/crusts in certain areas. This will be something to look out for today. (The Seattle Ridge sensor is rimed up and the Sunburst station has a battery issue we are working on).

Sluffs:  Watch your sluff if heading for the steep terrain. With such weakly bonded snow on the surface, triggering a loose snow avalanche on slopes 40 degrees and steeper is likely. These sluffs could be quick enough and carry enough momentum/volume to be a concern on the longer sustained slopes.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

With all the cold weather we have seen in the past 6 weeks, we have developed several weak layers in our thin snowpack. These are composed of two of the ‘classic’ persistent grain types: facets and buried surface hoar. These weak layers are still present, but the ‘slab’ that sits on them has decomposed and become faceted in most places – without a slab, you can’t have a slab avalanche. The exception are steep rocky slopes where old wind slabs, still stiff enough to be a slab, sit unsupported on weak layers. If you venture to these areas, watch for old stiff wind slabs and if one does release and knock you off your feet, where would you go?

Photo:  Buried surface hoar found under a thick old wind slab. Pit results showed that with a big force, the layer could fail and propagate; unlikely but not impossible in the very steep zones.

 

Surface Conditions??  We are set up again with a very weak foundation once the next snowfall hits.
   

 

 

Additional Concern
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Although cornices are pretty frozen in place, breaking off one of these, or a chunk, is still possible while on ridgelines.

Weather
Fri, December 23rd, 2016

Yesterday’s first day with gaining daylight (11 seconds) was bluebird with light and variable winds. Temperatures were in the single digits in the parking lots at 1,000′ and near 10F on the ridgetops.

Today, we should see sunny skies with winds bumping up slightly from the North and West to the 5-10mph range. Temperatures are forecast to be slightly warmer, in the teens at all elevations.  

Looking ahead to the Christmas weekend: A large low pressure is headed our way. Southerly winds should pick up along with high clouds tomorrow morning before the precipitation. The system is bringing warmer air and we could see rain at sea level but snow at 1,000′.

NWS forecast discussion:

“Strong winds coinciding with moderate to heavy
snowfall could produce blizzard conditions in turnagain Pass and
Portage Valley Sat afternoon through Sat night. There is still
some uncertainty as to the degree of warming that will occur in
Portage Valley. Temps in this area could rise into the mid 30s Sat
evening and produce a fairly wet snow or mix and mitigate the
potential for blowing snow. Turnagain pass should safely stay all
snow through Sat night. That said, issued a blizzard watch for
both areas.”

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 11   0   0   25  
Summit Lake (1400′) 1   0    0 8  
Alyeska Mid (1700′) 13   0   0   17  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) Under repair   Under repair     Under repair     Under repair    
Seattle Ridge (2400′) 12   Rimed   Rimed     Rimed    
Observations
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Riding Areas
Updated Mon, December 02nd, 2019

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
Closed.
Placer River
Closed
Closed.
Skookum Drainage
Closed
Closed.
Turnagain Pass
Closed
Closed.
Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
Closed.
Lost Lake Trail
Closed
Closed.
Primrose Trail
Closed
Closed.
Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
Closed.
South Fork Snow River Corridor
Closed
Closed.
Summit Lake
Closed
Closed.

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