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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
Thu, December 12th, 2019 - 7:00AM
Expires
Fri, December 13th, 2019 - 7:00AM
Forecaster
Ryan Van Luit
The Bottom Line

Today, above 2500′ the danger is CONSIDERABLE where natural avalanches are possible and human triggered avalanches are likely. East winds persist and snow continues to accumulate above 3000′ creating wind slabs and growing cornices throughout the region.  The persistent warm temperatures are making the snowpack thin up to 2500′. It’s a great day to tune your gear!

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Thu, December 12th, 2019
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)
Recent Avalanches


Glide avalanche on Raggedtop, most likely released Tuesday morning, Dec 10th.

Glide avalanches in the Girdwood valley, like this one near Raggedtop, have been reported over the past two days.  Aside from that, the advisory area has experienced no avalanche activity that we know of since the cycle on Monday, Dec 9th.  We also didn’t see any new activity yesterday in the Summit Lake area.

Avalanche Problem 1
  • 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
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

Up in the high elevation terrain where dry snow exists, wind slabs have been forming in the lee of ridges and gullies since Dec. 9. Ridgetop winds have been persistent and steady from the east and averaging over 30mph over the last 24 hours. This combined with a few inches of new snow from last night and a chance for a few more inches today will keep wind slabs, along with cornice falls, a primary concern. Choose your routes carefully and retreat if the snow beneath you becomes stiff and hollow sounding.

 

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

Rain up to 3000′ transitions to snow above, which is adding more snow and stress to a persistent weak layer in the higher terrain above 3,000′. We’ve been tracking a layer of facets sitting over a crust near the ground. Our snowpack stability tests consistently indicated this layer was stubborn, but reactive and planar before these series of storms rolled through. Until we know more, we are still concerned it could become overloaded and produce a larger avalanche breaking near the ground.

Snow depths are minimal up to ~1500′.  Near 2500′ and above, snow depths range from 3-6′ where snow is accumulating.

Additional Concern
  • 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

There have been reports of glide cracks and releases within the Girdwood Valley (see photo above).  We’ll continue to monitor if this is a trend throughout the advisory area. Glide avalanche failure is difficult to predict – stay out from underneath these cracks!

Weather
Thu, December 12th, 2019

Yesterday: Cloudy skies with above freezing temperatures were seen all day and overnight up to 2500′.  Around .5″ of rain fell in the afternoon and overnight in Girdwood and Turnagain Pass up to 2000′. Ridgetop winds have been persistent, averaging from 25-35 mph with gusts to 60 mph.

Today: Cloudy skies with intermittent rain below 2,000′ through late afternoon, then possibly transitioning to snow as temperatures push toward freezing at 1,000′. Roughly .25″ of rain is forecast today with another .5 possible tonight, equating to a total of 5-8″ of snow by tomorrow morning in the Alpine.  Easterly winds will continue to move warm Gulf air and moisture into the region.  Ridgetop winds should back off slightly today to the 10-20 mph range with gusts to 40mph.

Tomorrow: Cloudy skies with light precipitation will continue as this Gulf low slowly works its way out of the region. Temperatures will remain near 40F at sea level and 30 F at 3,000′.  Persistent moderate to strong winds are expected to continue out of the east.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 37 0 0.5 18
Summit Lake (1400′) 37 0 0 7
Alyeska Mid (1700′) 36 0 0.4 12

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 29 ENE 31 61
Seattle Ridge (2400′) N/A* N/A* N/A* N/A*

*Seattle Ridge weather station is down and as soon as the weather clears we will get it up and running!

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Riding Areas
Updated Mon, October 26th, 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
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.