Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, December 15th, 2017 - 7:00AM
Expires
Sat, December 16th, 2017 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is  CONSIDERABLE  on all aspects in the Alpine, 2500′ and above. Triggering deep slab, 4-8+’ deep, and/or  a fresh wind slab 1-2′ is likely  on slopes steeper than 30 degrees. Cautious route-finding and conservative decision-making are essential.  

2500′ and below the avalanche danger is  MODERATE  where  rain has fallen  and  a melt-freeze crust has developed. Triggering a slab avalanche is still possible.  

Below 1000′, where little snow exists, there is no danger rating.  

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Fri, December 15th, 2017
Alpine
Above 2,500'
Considerable (3)
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
Considerable (3)
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
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
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.

Likelihood of Avalanches
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.
More info at Avalanche.org

Above 2,500′ moist to dry snow has fallen for two weeks now. We have little information for these upper elevations at this time, but we do know prior to the storm cycle weak faceted snow with crust(s) sat near the ground. Prior to this last warm, wet storm this set-up was very reactive and there were multiple remote triggered avalanches. The slab on top of this weak foundation has now grown to several feet. This presents a deep persistent slab problem and will be guilty until proven innocent.  The 1st person on the slope or the 10th might trigger this type of avalanche. It is a total roll of the dice or Russian roulette set-up. Finding the shallow spot could have devastating results. This type of avalanche would be unsurvivable. There may be no obvious clues to indicate instability and digging to find the weak layer could be challenging. We need more time and information to determine the sensitivity and distribution of the deep persistent slab problemConservative route-finding will be essential due to the potential for large avalanches. 

Below 2500′ where rain fell the snowpack is a mixture of crusts and wet snow. Runnels are present and the facets near the ground are moist to wet and rounding. The cooling trend is locking up the snowpack. Triggering an avalanche is still possible but does not have the same potential for the large destructive deep slabs. Pay attention to your elevation bands today and as always look for signs of instability. 

Deep slab avalanches are like messing with a sleeping dragon. You might tiptoe around it but waking the dragon up will be terrible. Avoidance is key!

4-6+ inches of water weight, multiple feet of snow, now rest on top of this snowpack structure observed on December 8th. 

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

Likelihood of Avalanches
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. Small avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become large enough to bury, injure, or kill people, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

In the Alpine there is plenty of new snow to blow around and an additional 2-6″ is forecasted to fall throughout the day. Easterly winds gusting into the 40s will load leeward slopes today and triggering a fresh wind slab will be likely. Look for drifting and cracking and avoid hollow sounding snow. These same slopes may also have a deep slab problem. Triggering an avalanche in the upper snowpack may have the potential step down. 

Video from the National Avalanche Center Encyclopedia

Weather
Fri, December 15th, 2017

Yesterday was overcast with light snow showers on and off throughout the day.   Easterly winds were light 5-10 with a few gusts into the teens. Temperatures were in the mid 20Fs to low 30Fs. There was a cooling trend overnight.  

Today is forecasted to be mostly cloudy with snow showers during the day with snow likely tonight. 2-6″ of snow expected to fall today and 4-10″ tonight. Temperatures will be in the mid 20Fs to low 30Fs. Winds will be easterly 15-25 gusting into the 40s. Rain/snow line will be approximately 500′ today dropping to sea level tonight.  

Tomorrow should see continued snow showers, decreasing winds and cooler temperatures. According to the National Weather Service, “The long term will continue to see rather active weather, though  cooler (more seasonable) temperatures should move back in.” #snowtosealevel

* Sunburst weather station is down due to loss of battery power.
** Seattle Ridge anemometer is rimed and not reporting.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30    0  0 25  
Summit Lake (1400′) 28  0  0 9  
Alyeska Mid (1700′) 30  0  0  18

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) *n/a   *n/a   *n/a   *n/a  
Seattle Ridge (2400′)  25 **n/a   **n/a    **n/a
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Riding Areas
Updated Wed, December 11th, 2019

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
Glacier District
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Closed
Closed.
Placer River
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Skookum Drainage
Closed
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Turnagain Pass
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Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
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Lost Lake Trail
Closed
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Primrose Trail
Closed
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Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
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South Fork Snow River Corridor
Closed
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Summit Lake
Closed
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