Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, February 1st, 2017 - 7:00AM
Expires
Thu, February 2nd, 2017 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is  MODERATE  in the Turnagain Pass area. On slopes over 35 degrees and above ~1,000′, it is possible to trigger a wind slab on wind loaded slopes and  there is the possibility of triggering a large (2-3′) persistent slab avalanche that breaks lower in the snowpack. In addition cornice falls are still a concern.  Below 1,000′ the danger is  LOW.

Girdwood Valley:  Persistent slab avalanches have the potential to be larger, over 3′ thick, and break near the ground on weak faceted snow.  

Summit Lake:  Dangerous human triggered slab avalanche conditions persist in the Summit Lake zone. Check out the Saturday Summit Summary  HERE.  

**The probability of triggering one of these large slabs is decreasing but the consequences remain high. Be sure to  carry your rescue gear and practice safe travel protocol – such as exposing one person at a time, grouping up in safe zones, having escape routes planned and watching your partners!  

 

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Wed, February 1st, 2017
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
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
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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

Active wind loading was observed yesterday and Easterly winds were in the 20s gusting into the 40s for most of the day.  Today wind slabs will be possible to trigger on steep wind loaded (both top and cross loaded) slopes. These may be 6″ to 2′ thick. It will be important to look for pillowed or drifted areas and watch for shooting cracks. These slabs may allow you get out onto them before they break. In some places fresh wind slabs are sitting on old wind slabs and more than one layer might be triggered. Avoid areas with hollow sounding snow. A skier on Monday found a cross-loaded pocket on Sunburst and triggered a small wind slab on a convex roll. 

Cross-loading. Photo: National Avalanche Center 

Cross loaded slopes Seattle Ridge 1.30.17

 

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

The January 26th warm storm event added 2-3′ of snow to the upper elevations and rain at lower elevations. This event overloaded a variety of weak layers in the pre-existing snowpack and caused a widespread avalanche cycle in the region. The good news is the snowpack is showing signs of adjusting to the load, the bad news is that there is still potential to trigger a persistent slab avalanche if you find the wrong spot. This can make for difficult snowpack assessment as the weak layers of concern (depth hoar, facets and buried surface hoar) are lurking anywhere from 2-4+ feet below the surface. Thicker snowpacks, as found at on the North end of the Turnagain Pass had a stronger snowpack to begin with and this has been a big factor in the area beginning to adjust quicker. This is opposed to the persisting unstable snowpack found South of Turnagain Pass and in the Girdwood Valley. The other factor to consider is potentially different snowpack depths and structure on different aspects due to the multiple wind events stripping slopes and loading slopes. Generally speaking Southerly and Easterly slopes are thicker while Westerly and Northerly are thinner. The thinner aspects even on the Northern end of Turnagain Pass have a more suspect structure with slabs resting on more developed facets. As always pay attention to signs of instability i.e. cracking, collapsing (whumpfing) and recent avalanches but be aware that they may not be present with this type of avalanche concern. 

In general – this is a high consequence but low probability situation. If choosing to ride or ski the steeper terrain, we recommend using safe travel protocol, especially exposing one person at a time and grouping up in safe zones. If a large slab is triggered it may run further than expected and wrap around terrain features taking out mid-slope relative safe zones. Since the weak layers in question are fairly deep, it will likely take finding a thin spot in the slab or a big trigger to initiate an avalanche. 

Snow pit @ 2200′ on the NW shoulder of Magnum. Stiff wind slab over weak faceted snow at the base of the snowpack.

 

 

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

Give cornices wide berth, avoid travel on slopes below them and remember they can break farther back onto the ridge than expected.  If cornices do break and fall they could trigger an avalanche on the slope below.

Weather
Wed, February 1st, 2017

Yesterday was cloudy and there was very light snow/rain showers on and off throughout the day (depending on location and elevation).  Easterly winds were in the 20s and gusted into the 40s. Temperatures were in the 30s below 1000′ and mid to low 20s towards ridge tops. There was slight cooling overnight.  

There is a chance of snow showers this morning with an overall clearing trend forecasted for this afternoon into the evening. Temperatures will 20s at upper elevations and 30s at sea level. Winds will start easterly 5-15 mph and shift to the North and may bump up with the outflow this evening. The weather for the remainder of the week looks to be dominated by blocking pattern that will bring sunny skies and cooler temperatures into the weekend.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  32  trace  0 57  
Summit Lake (1400′)  28  1  .1  25
Alyeska Mid (1700′)  30  2  .1  51

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  21  ENE 22    47
Seattle Ridge (2400′)  24  SE 15  30
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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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