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Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, February 12th, 2020 - 7:00AM
Expires
Thu, February 13th, 2020 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is CONSIDERABLE at all elevations. With new snow, rising temperatures and strong winds overnight, triggering a storm slab is likely and natural avalanches are possible. In addition, triggering a large and dangerous slab avalanche 2-4′ thick on buried weak layers is possible and these avalanches may be triggered remotely. Conservative travel and decision-making are essential today.

There is a Winter Weather Advisory in effect until 9 am this morning.

PORTAGE: Natural avalanches have the potential to hit the Byron Glacier trail and the lake.

REGION-WIDE: Heads up! Strong winds have created dangerous slab avalanche conditions from Seward to Hatcher Pass. Extra Caution is advised. Choose terrain very carefully. Check out these recent observations and the Hatcher Pass Avalanche Center Facebook page for more information.

 

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Wed, February 12th, 2020
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

PRELIMINARY ACCIDENT INFORMATION: February 10th, Boulder Creek Drainage, South of Cooper Landing. Link HERE. This occurred outside of the CNFAIC forecast area.

*A final report is being compiled as we continue to gather additional information. It will be posted as soon as possible. Our deepest condolences go out to the family, friends, and everyone affected at this difficult time.

View of avalanche looking to the north. The snowmachines and people are investigating the site. 2.11.20. 

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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
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

The already dangerous snowpack is getting loaded again! Please choose terrain very carefully. Alyeska Resort is a great option today or riding in the flats well away from the runout of avalanche terrain. The region picked up 5-10″ of snow overnight with the Portage area being favored and it is still snowing this morning. Winds were easterly averaging 15-25 mph overnight and gusting into the 50s and are still at it this morning. Temperatures rose into the high 20s and with some sea level locations reaching the mid 30s. All these factors combined create the recipe for new storm slabs 6″ to a foot deep and potentially deeper wind slabs in exposed terrain. The temperature increase and/or the wind effect will likely make the snow feel upside down with heavier snow over lighter snow. In addition, this all could overload already dangerous slabs sitting on buried weak layers and step down creating a much larger avalanche (please see Avalanche Problem 2). Look for cracking in the new snow, drifting and wind texture at upper elevations and remember 2-4′ below the surface lurks a very dangerous snowpack structure.

Wind slabs: There is also older wind effected snow just below the new snow from the NW wind event on Monday that could also be potentially triggered in steep terrain. Leeward i.e. loaded terrain for that event was opposite from the loading last night. This is another complexity of the current snowpack.

Loose snow avalanches: Below treeline heavy wet snow may cause loose snow avalanches.

Snowfall this morning at Turnagain Pass at the DOT snow stake.

Avalanche Problem 2
  • 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

Triggering a very large unsurvivable avalanche is a very real possibility today. It has been CONSIDERABLE avalanche danger for two weeks. That is a long stretch to have such dangerous conditions and is unfortunately the nature of a persistent slab problem. We don’t see this issue healing up anytime soon. Each snowfall and wind event have incrementally loaded the very weak snow that formed in January. Warming temperatures have made the upper layers of snow even more cohesive/slabby.  There have very large human triggered and natural avalanches observed and avalanches have been triggered remotely. The most recent avalanches observed were on Monday and were very large. Don’t get lured into terrain today by new snow and flirt with triggering a large slab avalanche. As you look ahead to clear skies tomorrow please dial back the fun meter. This snowpack deserves respect. An observer yesterday on Magnum said this was one of the spookiest set-ups he had ever seen and noted a large crown wrapping around Super Bowl that likely slid over the weekend and very large debris chunks in the gulley. Reading back through the observations really illustrates the snowpack issues and avalanche potential. This morning is a great day to do that!

Snowmachine triggered avalanche in 2nd bowl on the backside of Seattle ridge. This occurred 2.10.20. Photo: Travis Smith

Weather
Wed, February 12th, 2020

Yesterday: Yesterday was mostly overcast with some partly cloudy breaks. Temperatures rose steadily throughout the day starting in the single digits and low teens and hitting mid to high twenties overnight. Winds were light and westerly in the morning an shifted to the east and increased in the afternoon. Overnight winds were averaging in the 20s gusting into the 50s. Snow started falling around 9 pm with 4-6″ of accumulation overnight.

Today: Cloudy skies and snow, 2-6″ forecast and the potential for mixed precipitation at sea level. Temperatures will range from the mid thirties at sea level to low 20s in the Alpine. Winds will be easterly and gusty this morning shifting to the north and decreasing mid day becoming light. Scattered snow showers will continue in the evening. Skies clear overnight and temperatures drop into the single digits.

Tomorrow: Mostly clear skies as a ridge of high pressures sets up over the region. Temperatures will be in the teens and winds will be light and westerly. Looking ahead the next chance of snow is Saturday through the holiday weekend. Stay tuned!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 18 5 0.6 59
Summit Lake (1400′) 15 2 0.2 24
Alyeska Mid (1700′) 17 5 0.39 60

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 13 NE 15 57
Seattle Ridge (2400′) 17 SE 8 27
Observations
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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.