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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
Thu, April 26th, 2018 - 7:00AM
Expires
Fri, April 27th, 2018 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger is MODERATE, but may increase to CONSIDERABLE if the sun appears this afternoon. Triggering a wet avalanche is possible today on steep slopes below 2500′. If the sun comes out natural wet avalanches are possible in the afternoon in the alpine. It is also possible to trigger a storm slab 1-3′ deep in the alpine where drier snow exists. Cornice fall could trigger a storm slab or wet loose avalanche below.

**In Portage Valley where precipitation totals were much greater this week, be aware of popular hiking areas with avalanche terrain above like Byron Glacier trail. Some hikers last Saturday had a close call when an avalanche released naturally from above.  

Friday outlook: Similar weather is forecasted for tomorrow. Springtime conditions require constant evaluation of the snowpack and flexible objectives. Evaluate terrain and snowpack as you travel. Extra caution if solar radiation starts changing the snow.

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Thu, April 26th, 2018
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Wet Loose
    Wet Loose
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Triggering a wet avalanche is possible today where rain has saturated the snowpack in the mid and lower elevations. Daytime temperatures are expected to rise into the mid-40F’s in the lower elevations and mid-30F’s to 2500’. Today’s forecast is calling for scattered rain showers (0.15” of rain) below 2300’. As instability showers move through our region, patches of blue sky and sun are also possible at times. Today’s avalanche danger will depend on how warm it gets and if radiation from the sun impacts the snow. Even a little sun shining through thin cloud cover can create rapid warming of the snowpack. Expect surface snow to be wet and ’pushable’ in the mid elevations. Areas like Portage and Girdwood Valley that received more rain in the last few days, there is more potential for a wet avalanche to entrain deeper into the snowpack, and larger avalanches are possible. If the sun heats up dry snow in the upper elevations, natural wet snow avalanches could release naturally, especially near rocks or where chunks of cornice are shedding. Pay attention to how wet and saturated the snow feels. Is this the top 2 or 3” of wet snow or a deeper issue? If your skis or snowmachine start punching deeper into the snowpack, avoid all steep slopes. Triggering a wet avalanche, once it’s picked up momentum, can be difficult to manage. 

Water totals (inches of rain) in the last two days. New snow in the upper elevation since Tuesday could range from 1 to 3 feet (Turnagain Pass vs. Girdwood)  

  • Turnagain Pass:   0.5”    (1.6” total since Saturday)  
  • Girdwood Valley:  1.2”    (2.8” total  since Saturday)
  • Portage Valley:     2.4”    (7.4” total since Saturday)
  • Summit Lake:       0.1”    (0.3” total since Saturday)

Slopes above Byron Glacier trail have seen a lot of avalanche activity this week. Note the large cornice that still looms above, and rocks that can easily heat-up and shed snow with daily warming and sun.  

 

Visibility was limited yesterday, but we did see a few new natural wet loose avalanches on Seattle Ridge. This aspect has seen a lot of wet avalanche activity this season, but it doesn’t mean this aspect is done. Human triggered avalanches are still possible. Monitor how wet and saturated the snow is and how it changes throughout the day. 

Avalanche Problem 2
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

If you are heading out to catch new snow at higher elevations, extra caution is warranted where little information exists about how well the snowpack is adjusting. Storm slabs that formed on Tuesday due to heavy snow and strong winds could range from 1 to 3 feet deep depending on what part of the forecast zone you are in. Expect storm slabs to be deeper in Portage Valley and Girdwood. Any sun on solar heating could make them easier to trigger in the afternoon.  Evaluate snow and terrain carefully and ease into steep slopes with caution. Also be aware of slopes that suddenly change from drier snow in the upper elevation to wetter snow mid elevation.  

Upper elevation North aspects: Shaded aspects in the Alpine had a thin layer of facets and/or surface hoar over a crust under last week’s new snow. This layer may still be lurking, which could result in slab avalanches 2 – 4+’ thick composed of couple of storm layers of snow.   

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

Warm and stormy weather this week has caused cornices to shed. There are some places, like Seattle Ridge where Cornices are large and challenging to judge if you are on them. Give them plenty of space and avoid being under cornices. Daily warming and any sun that might appear today will be adding additional stress. 

A brief clearing yesterday afternoon showed recent cornice fall below CFR on Tincan ~2400′.  

Weather
Thu, April 26th, 2018

On Tuesday an impactful storm front moved through our region bringing strong winds, periods of heavy rain and snow to our region. Turnagain Pass remained on the drier side with 0.4 € of rain that tapered off Tuesday night and 0.1 € was recorded in the last 24 hours. Portage on the other hand had near 2 € of rain on Tuesday and additional 0.4 € yesterday. Rain/snow line has fluctuated from 500′ to 2000′, but daily warming yesterday showed a period of above freezing temperatures as high as 2400′ on Seattle Ridge.   Winds on Sunburst were Easterly and averaged 24mph with gusts reaching the 90’s mph on Tuesday. Yesterday winds were moderate from the East 15-30mph.  

Mostly cloudy skies and scattered rain showers will continue across our region with up to 0.15 € of rain possible. This could be 1-2 € of new snow above 2500′. Temperatures could range from the mid-40F’s at sea level to mid-30F’s in the mid elevations. Easterly ridgetop winds are expected to be 10-20mph.  

Tomorrow looks similar with more scattered rain and snow showers on tap. Daily temperatures swings will range from 40F’s during the day to low 30F’s at night near sea level. Cooler temps in the alpine.   Winds will remain moderate from the East. A similar pattern is expected through the weekend.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 36    0 0.1   65  
Summit Lake (1400′) 36   0   0   18  
Alyeska Mid (1700′) 35   0   0.03   65  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24   ENE   14   34  
Seattle Ridge (2400′) 30   ESE   14    36
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Riding Areas
Updated Fri, May 01st, 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
Closed as of May 1. Thanks for a fun, safe season!
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
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Resurrection Pass Trail
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Snug Harbor
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South Fork Snow River Corridor
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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.