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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, February 2nd, 2019 - 7:00AM
Expires
Sun, February 3rd, 2019 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger remains a ‘scary’ MODERATE on slopes above 2,000′. Large unsurviveable slab avalanches, up to 5′ deep, remain possible to trigger on slopes steeper than 30 degrees. Several tracks may be on a slope before it slides, as was the case yesterday with two large human triggered avalanches. These avalanches can be triggered remotely – from the ridge above, the sides or below. This is a very tricky and dangerous avalanche problem that deserves our respect.

SUMMIT LAKE / JOHNSON PASS:    Human triggered slab avalanches 1-3′ deep are possible above treeline as a variety of weak layers exist in the snowpack. Wind loaded slopes are the most suspect for triggering an avalanche.  

LOST LAKE:   We have had reports that avalanches are being easily triggered on wind loaded slopes in the Lost Lake area. Heads up if you are headed this way!

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Sat, February 2nd, 2019
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
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
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "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. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Keep your hackles up! Despite the calm weather over the past three days, large and dangerous human triggered avalanches remain possible. There were three of these triggered yesterday in the Seattle Creek drainage on the backside of Seattle Ridge. The avalanches were 2-5′ thick and 500-1,000+’ wide. Two were on the Widowmaker slide path in Main Bowl (1st Bowl) and the other on Jr’s Run in Jr’s Bowl (2nd Bowl). A synopsis for each avalanche is listed below; we will be gathering more details today. Thank you to the many folks in the area yesterday for sending in their photos and reports

The problem with the snowpack is a layer of buried surface hoar that sits 2-5′ below the surface. It was initially buried on January 22nd by 1-2+’ of snow then another 6-8″ of snow and wind last week. The layer is beginning to show signs of being more stubborn to trigger, meaning several people can ski or snowmachine a slope before someone accidentally finds a trigger spot and the whole slope slides. We are entering a Lower Probability, High Consequence situation and this is likely to last for quite a while. Some things to keep in mind if visibility is good enough for travel above the trees:

1-  This is a scary situation because the snowpack can ‘feel’ stable and ‘just fine’ even though it may be sitting near the tipping point.
2-  Hence, no signs of instability are likely to be present to clue us into an unstable slope.
3-  Remotely triggering an avalanche from the ridge, the sides or from below is possible, threatening others below.
4-  Save travel protocol and assessing the consequences of an avalanche are key (i.e., larger terrain = larger avalanches, is there a terrain trap  below?)
5-  Sticking to lower angle slopes (below 30 degrees) can be a great way to avoid avalanche issues.

Widowmaker main slide path:
A snowboarder triggered the main Widowmaker path from the very top of the ridge. There were 5-6 tracks on the slope prior. The slab pulled back to nearly flat ground, pulling the snowboarder off the ridge. The rider was able to quickly jump onto the bed surface and escape. The slab was 5′ thick where it was triggered and propagated the full width of the slope. Good radio communication with several groups allowed for a quick assessment that all were ok and no one was caught in the runout below. 

Widowmaker slide path, note the debris filling up terrain depressions. Debris reported to be up to 20′ deep in places. Photo: Jerry Mann.

 

Looking near at the crown of the left side of the main Widowmaker avalanche. 

 

Avalanche on the looker’s right side of the main Widowmaker path:
An hour or two after the main Widowmaker slide, a group of two people on the ridge remotely triggered a second avalanche on the looker’s right of the first. This path had 20+ skier/snowboarder and snowmachine tracks on it. Why it was not triggered earlier and two people 20-30′ away on the ridge did is not only hard to believe, but shows how tricky the snowpack is right now. Furthermore, this area was believed to have avalanched already last week, which should have removed the weak layer. No one was on the slope or in the runout when it slid.

Avalanche on the looker’s right of the main Widowmaker slide. This slope was reported to have slide last weekend and suspected to be a repeat avalanche on the same buried surface hoar weak layer. Photo: Jerry Mann.

 

Jr’s Run avalanche:
This avalanche was triggered remotely by snowmachiners on the ridge. The avalanche pulled out in lower angle terrain on the looker’s right side of the main gut as well as the steeper rollover on the left side of the gut. There were no tracks known of in this area before the avalanche was triggered. 

Jr’s avalanche seen from the air. Both crowns from either side of the main gut are visible.

 

Jr’s slide path with debris running all the way to valley bottom. Only the steeper portion of the slide can be seen in the photo.

Weather
Sat, February 2nd, 2019

Yesterday:   Overcast to clear skies were over the region. Ridgetop winds have been mostly light and variable over the past 24-hours with a few gusts up to 20mph from the east. Temperatures remained cool, in the teens along ridgetops and 20’sF at sea level and valley bottoms.  

Today:   Mostly clear skies this morning should give way to cloud cover as the next weather front moves in this evening. There is a chance for a few snow flurries to sea level but no accumulation is expected. Ridgetop winds are expected to be light and variable before turning easterly tonight and picking up to around 10mph. Temperatures look to stay in the teens along ridgelines and in the 20’s in valley bottoms.  

Tomorrow:   A strong southwest flow looks to develop over the Kenai and Eastern Turnagain Arm. This will bring increased southerly winds and the chance for 2-4″ of snow. Temperatures are expected to remain cool enough for snow to sea level until Monday when much warmer air arrives.  

*The Seattle Ridge anemometer (wind sensor) was destroyed. We are currently working to replace it.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 18   0   0   57  
Summit Lake (1400′) 12   0   0   23  
Alyeska Mid (1700′) 19   0   0   47  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 17   E    7 20  
Seattle Ridge (2400′) *N/A   *N/A
*N/A     *N/A    
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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
Glacier District
Johnson Pass
Closed
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Closed as of May 1. Thanks for a fun, safe season!
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
Closed
Resurrection Pass Trail
Closed
Snug Harbor
Closed
South Fork Snow River Corridor
Closed
Summit Lake
Closed

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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.