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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
Sat, April 22nd, 2017 - 7:00AM
Expires
Sun, April 23rd, 2017 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

Very warm temperatures overnight coupled with a warm day ahead will increase the avalanche danger to CONSIDERABLE  on slopes over 35 degrees on all aspects above 1,000′. Wet snow avalanches ranging from small to very large along with cornice falls could being releasing today and activity may increase into the next several days. On slopes with wet and mushy snow, human triggered wet snow avalanches are likely. Lastly, debris could run into snow-free zones below 1,000′, raising the danger to  MODERATE at this elevation.

HEADS UP:  The springtime melt-down is here and the snowpack is continuing to lose strength as a whole and slide off the mountains. Extra caution is advised this weekend as avalanches could begin to release on West, East and Northerly aspects (avalanches are already releasing on Southerly aspects).

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Sat, April 22nd, 2017
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
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
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

After almost 2 weeks of sunny skies and high pressure, clouds and a warm East wind have moved in. The big news is how last night’s cloud cover has trapped yesterday’s daytime heat. This morning temperatures are 10-15 degrees F warmer than they have been during the past week and we are expecting a very limited, to no, re-freeze of the snow surface. The only thing that would help the re-freeze would be the increased winds, but they are only blowing 10-20mph and bringing in warm temperatures, so the wind may not keep the snow as cool as one would expect. That said, with a lack of re-freeze it will not take much daytime warming, or direct sunshine to initiate wet slab or wet loose avalanches.

WET SLAB, WET LOOSE, GLIDE AVALANCHES and CORNICE FALLS:
Although these are different characters of avalanches, they are all occuring together as the mountains fall apart with the springtime melt down. Widespread natural wet avalanche activity has already been seen on Southerly aspects, but the more shaded Westerly through Northeast aspects have yet to fall apart. This could happen this weekend as cloud cover has enhanced warming on all aspects. If choosing a day in the mountians this weekend be aware natural avalanches are possible and could become likely by Sunday. Things to keep in mind:

  1. Did the snowpack re-freeze overnight in your location? A hard frozen snowpack is stable, a soft mushy snowpack is dangerous.
  2. Are you punching through a shallow crust into wet soggy snow? Also a sign the snowpack is weak and could avalanche.
  3. Do you see any recent avalanches (take a look at the photo below to help identify a recent vs. an old avalanche).
  4. Are you in a runout zone? Can an avalanche releasing above wash debris over your location? Avalanches can run into valley bottoms.
  5. Buried weak layers in the pack can make a small avalanche or sluff become bigger by propagating across the slope and/or stepping down.
  6. Wet avalanches are hard to escape if you get caught. A small slide can be deadly if it pushes you into a terrain trap.

 Recent avalanche on Seattle Ridge (released Friday, April 21st)


Cloud cover over Tincan Ridge – trapping in the daytime heat overnight

 

 

*For the complete snow science geek out there – make sure and check out the Beaded Stream snow temperature array at the top of treeline on Tincan. This instrument measures ground, snow and air temperature vertically: Starting from 15cm (6″) below the ground, there is a cable extending 4meters (12′) upward that has a temperatures sensor every 15cm. The warmup of the whole snowpack can be seen – right now at this location (2,350′ in a flat area) the pack is almost isothermal , which means all the same temperaure at 32F. This is important because it indicates the potential for natural wet avalanches to begin on shady Northerly aspects. 

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

Although technically glide avalanches are a different beast than wet avalanches, they were lumped into the discussion above because how we deal with them now is similar to wet avalanches – simply avoidance. Avoid being under glide cracks – there are several cracks along Seattle Ridge, Tincan Ridge and many other slopes in the region. Each day we have seen 1-2 new glide releases (The photo above of Seattle Ridge being the last known glide release). The number of releases should increase with the warm weather.

Additional Concern
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

Upper elevation Northerly aspects should be warmer today. The cold dry snow surface could be giving way to a moist and wet snow surface, if it didn’t already overnight. With the added warmth of the pack in these shaded zones, increased stress on underlying weak layers will be occurring. 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. As the snowpack warms up, these weak layers could re-activate and triggering a large slab avalanche is possible. This is a low probability, high consequence problem.

Keep these points in mind:  

  • It will take someone hitting a ‘thin spot’ in the slab, or a large trigger such as a snowmachine and/or groups of people or a cornice fall
  • There may be no signs of instability before the slope breaks
  • Several tracks may be on a slope before it releases
  • Stability tests may not produce any notable results
Weather
Sat, April 22nd, 2017

Cloudy skies (yes, cloudy for the first time in practically 2 weeks!) were over the region yesterday. Winds moved in with the clouds and over the past 24-hours ridgetops have been blowing 10-20mph with gusts in the 30’smph from the East. Temperatures warmed up to 50F at sea level, ~45F at 2,000′ and 30-35F along ridgetops yesterday. Overnight only a slight drop in temperature has been seen and all elevations.

Expect a cloudy, breezy and warm day today as we are on the Northern edge of a large trough digging in the Gulf to our South. Ridgetop winds should remain in the 10-20mph from the East while temperatures continue to be near 50F in the parking lots and 30-35F along ridgetops. There is a chance for a rain drop or two tonight, but most of the precipitation will be to the South near Seward.

For Sunday, we could see light rain in places as the frontal boundary associated with the Gulf trough sends some moisture our way. In general however, the forecast is for cloudy skies, warm temperatures and breezy winds.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 42   0   0   60  
Summit Lake (1400′) 41   0   0   19  
Alyeska Mid (1700′) 40   0   0   54  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 30 NE   38   16  
Seattle Ridge (2400′) 33   SE   30   13  
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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.