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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, February 20th, 2016 - 7:00AM
Expires
Sun, February 21st, 2016 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

A  MODERATE avalanche danger exists today for fresh wind slab avalanches and cornice falls in the Alpine terrain. Wind slabs, up to 1 foot thick, will be possible to trigger on wind loaded slopes due to strong winds along ridgetops overnight and continuing today. At the mid-elevations, glide avalanches remain a concern where any one of the countless glide cracks can release at any time.

 If you are headed to the Summit Lake area, there are different snowpack concerns, see the  Summit Lake Summary  for more information.  

** There is a fast moving storm scheduled to arrive late this afternoon. Up to a foot, or more of snow is forecast from this afternoon through tomorrow morning. Avalanche conditions will increase rapidly in response to heavy snowfall. Stay tuned on tomorrow’s advisory!  

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Sat, February 20th, 2016
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
  • 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

Today’s primary concern will focus on the increase in winds from overnight and the strong winds forecast for today. There is just enough loose snow available for transport that fresh wind slabs are likely to form along ridgelines and other exposed slopes. Watching for the usual suspects such as cracking in the snow, stiff snow over softer snow, and smooth wind loaded surfaces will be key. Cornices are also something to keep in mind and continue giving a wide berth to.

Ok, now to the impending change in weather and increase in avalanche danger for tomorrow:  With a potent storm system at the doorstep, we are taking stock of not only how much snow will fall this weekend (up to a foot or more by tomorrow), but what types of surfaces it will fall on to. For those that have been enjoying the sunny days on Turnagain Pass last week, you will know that variable snow surfaces exist. These are: sun crusts on Southerly slopes, wind crusts on various aspects at all elevations and ridgelines and last, an abundance of soft loose faceting snow. On top of all these surfaces sits a layer of surface hoar that is anywhere from a few mm in size up to 2cm in places. What this all means is, any new snow that falls will fall on a weak layer of some type, limiting bonding between the new and old snow. In some areas, like South aspects, there will be a crust under the weak layer making bonding even more difficult. The good news is, we have strong winds today ahead of the snow which can blow over the surface hoar and generally make this set up less scary. But, this is not a sure bet and time will have to tell.

Surface conditions as seen yesterday along Seattle Ridge:

1-2cm surface hoar on top of Seattle Ridge                                          1-2cm sun crust with 3mm surface hoar on Southerly slopes
 

Additional Concern
  • 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

We did not see, or have any reports, of any glide cracks that released yesterday. That said, it’s the year to know where these cracks are and limit time under them as they can release with no warning.

Photo: Graham Predeger looks over at a large glide crack on the West side of Main Bowl (1st Bowl).

Weather
Sat, February 20th, 2016

High clouds filtered over the region yesterday ahead of storm slated to move in this evening. During the past 24-hours winds have picked up slightly from the East along the ridgetops to the 10-20mph range and temperatures are holding steady, ~20F in the Alpine and ~30F at 1,000′.  

Today we should see mostly cloudy skies with winds increasing into the 25-35mph range from a generally East direction. These winds should be the main player in weather considering snowfall is not expected to begin in earnest till the afternoon. Once snowfall does begin, we could see up to 5″ of snow by this evening (.5″ of water equivalent) and another 5-10″ (~1″ water equivalent) by Sunday morning. The rain/snow line looks to be around sea level today then possibly raise as high as 1,000′ tonight.

For Sunday, the main storm system looks to move out rather quickly but lingering instability showers and decreasing winds could add several inches of quality snow to the area. Temperatures look remain cold enough for snow to 1,000′ for the duration of the storm. Stay tuned on tomorrow’s advisory!

The Seattle Ridge weather station is back up with wind information – finally!!  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26   0    0 101  
Summit Lake (1400′) 24   0   0   30  
Alyeska Mid (1700′) 28    0 0   85  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18   NE    13 39  
Seattle Ridge (2400′) 20   SE 17   39  
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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
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Turnagain Pass
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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.