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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, December 27th, 2014 - 7:00AM
Expires
Sun, December 28th, 2014 - 7:00AM
Forecaster
John Fitzgerald
The Bottom Line

The avalanche danger is MODERATE in the alpine today.   Dense slabs up to 3′ in depth could be triggered in steep upper elevation terrain.   These slabs sit on a layer of weak snow and have the potential to pull out entire slopes.

In addition recently formed pockets of wind slab up to 1′ deep may be triggered in very steep terrain above 2,500′.

At treeline the avalanche danger is LOW.   Remember that LOW does not mean NO.   In particular pay attention to groups above you when traveling in mid elevation areas with avalanche terrain directly above.   Human triggered avalanches from the higher elevations have the potential to run down into the mid elevations today.

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Sat, December 27th, 2014
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
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
Low (1)
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

Clear skies and good visibility will make it easier to travel into the alpine today.  If you find yourself venturing into steep upper elevation terrain you will need to minimize your exposure and treat all slopes above 35 degrees with suspicion.  A layer of buried surface hoar, which we have been tracking, remains intact on many slopes above 2,500’.  Sitting on top of this layer are 2-3’ dense slabs.  

These stiff slabs have the ability to support a lot of weight, especially where they are thickest.  That all changes when you get onto thinner spots of a slab.  It will be possible for multiple tracks to be put down on a slope without avalanching.  It is important to know that tracks do not equate to stability.

This type of slab/weak layer combo is notorious for catching people off guard days and weeks after a storm.  While we have seen signs of the weak layer gaining strength, we also have no snowpack information from any terrain above 3,500’.

If you decide to get onto bigger and steeper terrain today, it will be crucial to manage yourself and your group appropriately:

Avoid trigger points, such as steep rollovers and areas where the snowpack is thin.
Only expose one person at a time, utilize islands of safety, have an escape route, and communicate plans and decisions effectively.  

Keep in mind that it’s a roll of the dice on all terrain over 35 degrees above 2,500′.  Slabs have the potential to propagate across slopes and carry enough volume and speed to injure and bury a person.

Avalanche Problem 2
  • 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

If venturing into steep upper elevation terrain expect to encounter lingering unstable pockets of wind slab, especially on North aspects.  High winds from 2 days ago formed upside down slabs up to 1 foot in depth.  These slabs may be encountered in starting zones and along cross loaded gullies.  Staying off of snow in steep terrain (over 40 degrees) that has a hollow sound or produces shooting cracks will be the best way in managing this concern today.

Weather
Sat, December 27th, 2014

Yesterday was a mild day for weather around the area.   Winds were calm to light, and predominantly out of the West/Northwest.   Temperatures remained in the 20s F along ridge tops and around 30 F at sea level.   No new precipitation was recorded.

Today expect mainly clear skies with some valley fog as a ridge of high pressure is stationed over the area.   Ridge top winds will be light out of the Nothwest at 10 mph and temperatures at 1,000′ will be close to 30 F.

The next big weather event will involve warm and wet Southerly flow.   Expect above normal temperatures with snow beginning Sunday night changing over to rain by Monday up into the mid elevations.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28 0 0 30
Summit Lake (1400′) 25 0 0 7
Alyeska Mid (1700′) 29 0 0 24.1

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21 WNW 7 29
Seattle Ridge (2400′) 24 variable 5 16
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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.