Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, April 29th, 2017 - 7:00AM
Expires
Sun, April 30th, 2017 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is expected to remain at  MODERATE  on slopes above 1,000′ for wet avalanches this weekend. The danger  could rise to  CONSIDERABLE  by the early evening hours in the event of significant daytime warming. Keep in mind the snowpack continues to slowly warm and destabilize as it undergoes the springtime transition. Human triggered wet loose and wet slab avalanches are possible on slopes over 35 degrees with a wet snowpack.  Natural wet snow avalanches will also become possible later in the day as the snowpack becomes wet. Additionally, glide cracks continue to slowly creep open and can release without warning.  

There is a  LOW  avalanche danger below 1,000′ where little snow remains.  

Hiking on summer trails during the springtime warm-up (including the Byron Glacier trail, Crow Pass, etc).    Extra caution is advised for trails that cross under avalanche paths. The danger will increase in the afternoons with possibility of an avalanche occurring above that could send debris to snow-free zones.  

SUNDAY APRIL 30th AVALANCHE OUTLOOK:  The avalanche danger and issues will be the same for tomorrow, Sunday. For Monday however, heads up that a cooler storm system will be moving in and could increase the avalanche danger.

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Sat, April 29th, 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
  • 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

Cooler weather and a chance for a few snow flurries above 2,000′ should keep most of the springtime rapid warming at bay this weekend (and possibly into next week). That said, we are still seeing a handful of avalanches each day as the snowpack transitions from dry to wet. Most of these have been relatively small wet loose sluffs and glide releases. The most notable however, is a natural wet slab avalanche that occurred Thursday(ish) in the Girdwood Valley (photo/description below). This slide was on a Northerly aspect around treeline and illustrates how all aspects are suspect currently. During the past 2 days there has been some type of avalanche documented on North, West and South slopes (I’m betting there is an Easterly one out there as well).

The key for a safe day in the mountains is knowing what slopes are wet, saturated and unsupportable (unstable and dangerous) and what slopes are frozen (stable). This is not always as easy at it seems. Carefully monitor surface crusts throughout the day and be aware of steep terrain above you that may be heating up faster than you may expect. Steep rocky terrain baking in the sun can begin to produce wet sluffs, which could in turn trigger a wet slab, and send debris to valley bottoms where the surface is still frozen. 

WET SLAB, WET LOOSE and CORNICE FALLS – things to keep in mind if you are headed out: 

  1. Are you seeing recent avalanches?
  2. Is the snowpack frozen or wet and soggy?
  3. Are you punching through a shallow crust into wet soggy snow? A shallow re-freeze is still weak and could avalanche.
  4. Are you in a runout zone? Can an avalanche releasing above wash debris over your location?
  5. Buried weak layers in the pack can make a small avalanche or sluff larger by propagating across the slope and/or stepping down.

Recent large slab avalanche on Orca Ridge/Big League, North aspect – released sometime close to Thursday, April 27th. This slide looks to have started as a wet loose avalanche then stepped down to the mid-pack and then again to the ground around 1500′.

 

Skier triggered wet loose sluffs on the Southwest shoulder of Sunburst from Thursday/Friday (old crown from early April storm cycle in background)

 

Farthest left natural wet loose avalanche on the West face of Magnum is also from Thursday/Friday (April 27/28), many older dark and melted out loose snow avalanches from earlier in the week on the right of the face 

Avalanche Problem 2
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glide cracks are also opening up and releasing on many slopes in the region with the springtime melt-down. At times it can be difficult to tell the difference between glides and wet slab avalanches. But that is beside the point – both are dangerous. The way to manage glide avalanches is to stay out from under any slopes harboring glide cracks! Check out the photo below from the motorized up-track. This slope is notorious for producing glide avalanches. Additional glide avalanche activity is expected today and through the week.

 

Note the opening glide cracks lower on Eddies West facing slopes?

 

Recent large glide avalanche on the lower Southwest facing Tincan terrain – in this area several glide cracks have released while several cracks and hanging in the balance.

Additional Concern
  • 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

There are several buried persistent weak layers in the snowpack; ranging from buried surface hoar 2-6′ deep, mid-pack facets and facets near the ground. Shallow snowpack zones such as the Summit Lake area harbor depth hoar near the ground. On upper elevation North, West and Easterly aspects these weak layers could re-activate when the snowpack melts, becomes saturated and loses strength. If significant warming/melting occurs this weekend or into the workweek, keep in mind large slab avalanches are possible – both triggered by a person as well as naturally.

Weather
Sat, April 29th, 2017

Partly cloudy skies with patches of sun filled the region yesterday before clouds moved in overnight with light precipitation; rain showers up to 1,500′ and some wet flurries above this. Up to .1″ of measureable precipitation fell in certain areas. Ridgetop winds have been moderate from the East, 10-20mph averages and stronger gusts. Temperatures have been cooler with ridgetops in the upper 20’sF and parking lot temperatures around 1,000′ in the low 40’sF during the day.

For today and Sunday: As we remain in between large scale weather patterns we can expect partly cloudy skies with intermittent showers. This should give the area a chance for rain up to 1,500′-2,000′ and snow above – intermixed with patches of sunshine. Ridgetop winds are expected to be light in the 5-10 mph range from the East. Temperatures will continue to be cool with ridgelines in the 20’sF and at 1,000′ in the low 40’sF.

Monday and early next week:  A cool low-pressure storm system will move in bringing rain to 1,000′-2,000′ and wet snow above this. Easterly ridgetop winds will increase into the 20’s and 30’s mph. Keep tabs on the recent weather on our weather page  along with the NWS forecast discussion!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 39   trace   0.1   51  
Summit Lake (1400′) 38   0   0   11  
Alyeska Mid (1700′) 37   trace 0.01   47  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 28   NE   8   25  
Seattle Ridge (2400′) No Data   SE   17   30  
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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

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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.