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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, January 6th, 2024 - 7:00AM
Expires
Sun, January 7th, 2024 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′ today. Winds are expected to increase dramatically throughout the day, which will increase the likelihood of natural and human triggered wind slab avalanches 1-2′ deep at upper elevations. Human triggered avalanches are still possible 1.5-3′ deep underneath the new storm snow from this week, although there is a lot of uncertainty about the potential to trigger an avalanche on this layer. Glide avalanches are also possible and it is important to avoid spending time underneath glide cracks. Below 1000′ the avalanche danger is MODERATE.

Special Announcements

Girdwood Forecaster Chat – Friday, Jan 19th!
Mark your calendars for Andrew Schauer’s discussion on the different shades of MODERATE danger at the Girdwood Brewing Co. (6:30pm Jan 19). More details HERE.

Sat, January 6th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Sun, January 7th, 2024
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
Avalanche risk
Sun, January 7th, 2024
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
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.
Recent Avalanches

We got limited information from the field yesterday and did not hear of any human triggered avalanches. The only avalanche reported was a glide release on Seattle Ridge on the ‘Repeat Offender’ slide path. This path is a major hazard for motorized folks heading up Seattle Ridge and it is a relief that it released without any known human involvement. Unfortunately there are multiple glide cracks in this area, so just because one released does not necessarily mean the glide problem is resolved for the Seattle uptrack.

Glide release on ‘Repeat Offender’, which is the avalanche path that looms over the Seattle Ridge uptrack. Photo Brian Murphy 1.5.24

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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

Today is looking like an ‘early bird gets the worm’ kind of day, with a brief calm period expected through midday before a strong storm front moves into the area. Winds will start off light, averaging 5-10 mph from the east, and gradually increase throughout the day. By this evening we are expecting east winds to average 40-60 mph with gusts of 80 mph+. Snowfall is expected to start around 3 pm today and continue throughout Sunday, with 15-30″ of new snow above 1000′ from Saturday afternoon through Sunday evening.

Our main concerns before the storm arrives are wind slabs at upper elevations and the lingering potential for a storm slab to release at the interface with the old snow surface. Yesterday’s windy weather likely formed wind slabs about 1′ deep along ridgelines at upper elevations. The increasing winds today will create a fresh batch of wind slabs 1-2′ deep. To monitor the development of fresh wind slabs keep an eye out for active wind transport along ridgelines and check for shooting cracks by getting off the skin track or trail in wind affected areas to get a feel for the snow.

The snow surface that was buried during Wednesday’s storm consisted of weak snow grains, like facets and surface hoar, which means it is still possible to trigger an avalanche at the interface between the storm layers. This interface is buried about 1.5-2′ deep in Turnagain Pass and Girdwood and closer to 2-3′ deep in Portage and Placer. Field observations the past few days have showed mixed results on whether this layer is still concerning or not, but since there is the potential to trigger a large avalanche on this layer we recommend a cautious approach to avalanche terrain today. You can use small, steep test slopes to check how well the new snow is bonding to the old snow surface and dig into the snow using hand pits or snow pits to get a little more information about this layer in the area you are travelling. If you want to avoid the problem entirely you can always stick to lower angle terrain.

Snowpit test that failed at the interface with the old snow surface about 2′ deep. Photo 1.4.24

Avalanche Problem 2
  • Glide Avalanches
    Glide Avalanches
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.

Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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 glide avalanche mayhem continues, with a fresh release reported above the Seattle Ridge uptrack yesterday. It is important to be vigilant and continuously assess the terrain above you to identify glide cracks. We recommend avoiding spending time underneath glide cracks altogether, but if it is unavoidable you can spread out your group and move as quickly as possible. When these avalanches release they take the whole snowpack, which results in a very large and destructive avalanche.

Large glide crack lurking under the Tincan Library. Photo 1.4.24

Weather
Sat, January 6th, 2024

Yesterday: Mostly cloudy with periods of broken sky cover and temperatures in the low 20s F at upper elevations and high 20s to low 30s F at lower elevations. No significant new snowfall. Winds were moderate yesterday morning, with averages of 10-20 mph and gusts to 35 mph out of the east, and gradually decreased throughout the day to averages of 5-10 mph and gusts to 20 mph out of the east in the evening and overnight.

Today: Saturday will be the calm period before the next big storm moves into the forecast area. Winds are expected to start off averaging 5-10 mph out of the east this morning and gradually increase to averages of 20-35 mph out of the east this afternoon. Overnight tonight the winds will continue to increase, with averages of 40-60 mph and gusts of 100 mph possible early Sunday morning. Along with the strong winds will come another round of snow, which will start off light around 3pm and become more intense overnight. Between Saturday afternoon and Sunday at 7am we are expecting 5-7″ of new snow. Rain line should remain in the range of 400-700′ throughout the storm.

Tomorrow: The peak intensity for snowfall is expected to be Sunday morning, with an additional 14-18″ of new snow expected to fall from Sunday morning through Sunday evening. Strong winds will persist throughout the day on Sunday with averages of 50-60 mph and gusts of 80 mph+ out of the east. Rain line is expected to remain at 500-700′ throughout Sunday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26 0 0.0 84
Summit Lake (1400′) 23 0 0.0 N/A
Alyeska Mid (1700′) 29 trace 0.03 76
Bear Valley – Portage (132′) 35 rain 0.28
Grouse Ck – Seward (700′) 33 2 0.2 51

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21 ENE 10 36
Seattle Ridge (2400′) 24 SE 6 17
Observations
Recent Observations for Turnagain Pass
Date Region Location
02/24/24 Turnagain Observation: TinCan Backdoor/ Center Ridge
02/22/24 Turnagain Avalanche: Lynx Creek
02/22/24 Turnagain Observation: Turnagain, Seattle, Mt Ascension
02/21/24 Turnagain Observation: Tincan Trees
02/21/24 Turnagain Observation: Sunburst
02/20/24 Turnagain Avalanche: Tincan
02/20/24 Turnagain Observation: Seward Highway across from Johnson Pass TH
02/19/24 Turnagain Avalanche: Base of Seattle Ridge
02/18/24 Turnagain Observation: Lynx creek
02/18/24 Turnagain Observation: Tincan Trees
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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.