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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, March 22nd, 2015 - 7:00AM
Expires
Mon, March 23rd, 2015 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is MODERATE on all aspects near and above treeline (above 2,000′).  Slabs up to 3′ thick resting on weak faceted snow may be triggered by the weight of a person in isolated areas. Additionally, daytime warming and spring-like conditions will increase cornice sensitivity and the potential for wet avalanches late in the day on Southerly aspects.

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Sun, March 22nd, 2015
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
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
No Rating (0)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • 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

Variability continues to be the theme of this weekend’s snowpack. Slabs 1-3 ft thick that formed over the past week rest on a variety of surfaces.  In some places the slab is bonded well to what is below, while in others it sits on a layer of facets that still have the potential to propagate and avalanche.

Where do the pockets of facets exist? The complexity of the current situation is trying to figure this out. You could dig in one spot and 10 ft over have a completely different structure. Some areas avalanched during the Post St. Patty’s day storm and then were covered up by the next snow on Thursday hiding the evidence and adding to the tricky nature of this snowpack. The facets may have been blown away by winds before the storms higher on the slope yet part way down the run be present and reactive.  Obvious clues may not be seen, however collapsing (whoomphing) does continue to be observed in certain areas and is a sure sign that facets exist in that location (photo below).

These conditions can be the type that allow multiple folks to travel down the slope before one hits the sour spot and triggers an avalanche. If you choose to go into avalanche terrain the potential of a slab/facet setup needs to considered and respected.  

Use good travel practices: travel one at a time, have escape routes planned and avoid trigger points and terrain traps. Be cautious on slopes 35 degrees or steeper.

Avalanche Problem 2
  • 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

Cornices have grown significantly from the past week’s storms and are hazards in some areas.

Warming throughout the day can make these more likely to release naturally or under the weight of a traveler. Give them a wide berth while traveling below or next to and remember they often break farther back than you expect.  The extra load of a falling cornice can trigger an avalanche if there is unstable snow where it lands.

Additional Concern
  • 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

It’s springtime! By late in the day yesterday (~4-5pm) the snowpack below 2,000′ became wet and unsupportable while the upper elevations became damp; these surfaces have refrozen overnight. Warming should be expected again today and as the snow heats up, wet loose “push-a-lanches” will be possible on steep slopes. Although it’s more of an outlier, there is a chance for pulling out a wet slab in areas with poor snowpack structure basking in the sun.

Weather
Sun, March 22nd, 2015

It was very warm and mild yesterday as thin clouds filled the skies and lowered visibility to mostly “gray bird” conditions. Temperatures reached the low 40’s at 1,000′ and near 32F on the ridgetops. Winds were light and variable with no precipitation since Thursday.  

Today, another warm day is in store with mostly sunny skies. Temperatures should reach the mid 30’sF on the ridgetops and low 40’s in the parking lots once again. Ridgetop winds will continue to be light and variable.

This mild spring-like weather should remain until Tuesday afternoon when a large North Pacific low develops and looks to usher in a warm, wet and windy storm.  

“Greenhouse effect”? Yesterday we saw what avalanche practitioners call a greenhouse effect, or “greenhousing”. This is when there is a  thin layer of clouds that let much of the solar radiation in but then also trap the longwave radiation, not allowing it to be released back into the atmosphere – essentially creating a blanket over the mountains which dampened the surface snow on all aspects. We may see this phenomenon again today if clouds filter in.

Today’s advisory is written with Aleph Johnston-Bloom, Executive Director of the Alaska Avlanche School.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 34   0   0   56  
Summit Lake (1400′) 32   0   0   12  
Alyeska Mid (1700′) 35   0   0   32  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 28   var   3    14
Seattle Ridge (2400′) 29   var   9     18  

 

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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

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Closed as of May 1. Thanks for a fun, safe season!
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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.