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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, January 12th, 2015 - 7:00AM
Expires
Tue, January 13th, 2015 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

Today the avalanche danger is MODERATE at treeline. Unusual spring-like conditions are causing an upside down danger rating. Today .21 inches of rain is expected up to 3500′; increasing the likelihood for wet avalanches and glide avalanches below 2500′. At higher elevations where cooler temperatures have formed a firm supportable crust the avalanche danger is LOW in the Alpine.

Over the last two days several natural glide avalanches have occurred and many glide cracks have grown in size. (See photos below) In general it is best to avoid traveling under or near these large frowning cracks.

Mon, January 12th, 2015
Alpine
Above 2,500'
1 - Low
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • 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

Over the last 4 days we’ve seen unusually warm temperatures above freezing at lower elevations, which has caused a lot of water to flow through the snowpack. Yesterday morning several glide avalanches were observed on the Eastern face of Seattle Ridge and the Southern face of Eddies, all below 2700′.  Today rain is expected throughout the day increasing the potential for more glide activity.

Glide avalanches are common to Alaska’s maritime snowpack and occur in steep terrain where the bed surface underneath is slick. These rather unpredictable avalanches are not associated with a human trigger. They seem to happen spontaneously during prolonged periods of warming when water has lubricated the ground; as observed by a Level 2 avalanche student yesterday in a snowpit on Seattle Ridge.

In general it is best to not travel underneath or in terrain where glide cracks have formed. Fortunately they seem to be more common in steep extreme terrain and are easy to identify, thus making them avoidable.

At higher elevations there are fewer glide cracks visible, but it is still wise to plan your travel around them. 

 

Two recent glide avalanches on the Eastern Face of Seattle Ridge were observed yesterday morning. Starting zone elevation is estimated between 2500′ – 2700′

 

Recent glide avalanches on Eddies South Face, elevation estimated at about 2500′. 

Avalanche Problem 2
  • 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

Today rain combined with above freezing temperatures is increasing the likelihood of wet loose avalanches at elevations below 2000’. Over the last 4 days a lot of water has drained through the snowpack causing the snow to become unconsolidated and wet at treeline. Rain today and into tonight could increase the likelihood of small human triggered wet loose avalanches on steep terrain features.

At higher elevations where temperatures have been cooler a solid melt/freeze crust has formed making this problem unlikely above 2000’.  Be aware of an area between 2000’ and 2500’ where breakable crust with moist snow below could be extra challenging to ski/ride through today.   

 

As of yesterday a very supportable melt/free crust has formed above 2500′. Notice the re-frozen rain runnels and old ski tracks on Tincan.  

Weather
Mon, January 12th, 2015

After an initial rain event on Jan. 8th this warm spring-like weather seems to be sticking around into this week. Over the last few days temperatures have been in the low to mid the 30’sF with a 3-day stretch of temps averaging 35F at Center Ridge (1880′) weather station. No new precipitation has been recorded since Jan.8th.

Yesterday temperatures were mild, in the high 20’sF at ridgetops and mid 30’sF at 1000′. Skies were patchy with isolated areas of light precipitation, but no accumulation in Turnagain Pass was recorded. Winds were light in the morning and East ridgetop winds picked up to 10-25mph throughout the day.

Today another low-pressure system continues to bring unusually warm January weather. We expect to see rain starting this afternoon, up to .21 inches at Turnagain Pass. Rain/snow line will be around 3500′. East winds should increase to 25-45mph at ridgetops.

Tonight precipitation is expected to increase with up to 1 inch of water and rain/snow line is expected to remain around 3500′.  East winds will continue to be 25-45mph at ridgetops.  

There is some talk later in the week of cooler air from the artic combined with moisture helping us keep our hopes up that snow may be in our future.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 35   0   0 29  
Summit Lake (1400′) 33   0   0   5  
Alyeska Mid (1700′) 35   0   0   22  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 28   E   13   34  
Seattle Ridge (2400′) 30   ENE   14   27  
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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.