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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, January 16th, 2024 - 7:00AM
Expires
Wed, January 17th, 2024 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger will start out MODERATE and rise to CONSIDERABLE above 2500′ this afternoon, as strong NW outflow winds are expected to pick up around 3pm. The chances of both natural and human triggered wind slab avalanches 1-2′ deep will increase quickly once the winds pick up and start transporting snow.

Glide avalanches are also a concern above 1000′, where the avalanche danger is MODERATE. These avalanches are very large and release randomly. It is important to keep an eye out for glide cracks above you and try to avoid hanging out underneath them. Deeper avalanches releasing 2-4′ deep on a buried weak layer are still a concern in the remote corners of the forecast area where we have limited information. Below 1000′ the avalanche danger is LOW. 

Summit Lake / Seward / Lost Lake: The NW outflow winds we are expecting this afternoon tend to impact these areas heavily. Avalanche danger will increase quickly once winds start to transport snow.

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.

Tue, January 16th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
Wed, January 17th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
Wed, January 17th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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

No new avalanches were reported yesterday. However, glide avalanches continue to release across the forecast area.

Close up of massive glide release near the Seattle Creek Uptrack from 1/14. Photo from Anonymous 1.15.24

 

Avalanche Problem 1
  • 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 active glide avalanche cycle continues across the forecast area. These can release at random and take the entire 5-7′ deep snowpack with them, creating very large and destructive avalanches. Thankfully the clear skies should make it easier to spot glide cracks today. During these periods where glide avalanches are occurring frequently it is important to be extra aware of the slopes above you and look for open glide cracks or a wrinkly snow texture to indicate where glide cracks exist. We recommend avoiding travelling underneath glide cracks, or if it is unavoidable try to minimize your time underneath.

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

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

NW outflow winds are expected to increase this afternoon, with averages of 20-30 mph and gusts up to 50 mph possible. These strong winds tend to be concentrated along gaps in the terrain where the cold interior air can escape to the coast. Common gap wind areas include Turnagain Arm, Portage, and Seward. Wind slabs have the potential to form quickly due to the soft snow currently on the surface. To identify areas with potential wind slabs keep an eye out for active snow transport, shooting cracks, or hollow and drum like snow in the area you are travelling. Due to the nature of how these gaps winds channel through the terrain, it is possible for wind slabs to form at lower elevations and in unusual locations versus our typical easterly storm winds.

Graphic courtesy of NWS Anchorage. 1.14.24

Additional Concern
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

We still have lingering concerns about the potential to trigger an avalanche on a buried weak layer 2-4′ deep. It has been just over a week since the last human triggered avalanche on a buried weak layer, so at this point we think it is unlikely for a person to trigger an avalanche like this. However, in the far flung corners of our forecast zone, like Johnson Pass, Lynx Creek, or Silvertip, where the snowpack tends to be thinner we still recommend evaluating the snowpack carefully to check for buried weak layers before committing to steep terrain.

Weather
Tue, January 16th, 2024

Yesterday: Clear skies and cooling temperatures, with highs in the teens F at mid and upper elevations and single digits F at lower elevations due to a temperature inversion. Winds were mostly light averaging 5-10 mph with gusts to 20 mph out of the NW. Gap winds started to increase, with higher winds in areas like Turnagain Arm and Seward. No new snowfall.

Today: High pressure continues to build across the region, with clear skies and cool temperatures expected today. Temperature inversions are likely in many areas, with current temps at the road in Turnagain Pass in the single digits F and closer to 20 F at ridgetop elevations. Winds are expected to remain light at 5-15 mph out of the NW through the afternoon. Around 3pm winds are expected to increase to 20-30 mph out of the N and temperatures will start to decrease towards single digits. Gap winds in areas like Turnagain Arm, Portage, and Seward are expected to increase dramatically this afternoon.

Tomorrow: Clear skies and cold temperatures in the low teens to single digits F will continue through Wednesday. Strong N winds will also continue to push through gaps as cold air tries to escape from the interior. Areas like Turnagain Arm, Seward, the Matanuska Valley, and Thompson Pass are expected to see very strong winds, with gusts up to 50-60 mph possible.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 15 0 0 82
Summit Lake (1400′) 7 0 0 NA
Alyeska Mid (1700′) 16 0 0 82
Bear Valley – Portage (132′) 15 0 0
Grouse Ck – Seward (700′) 15 0 0 51

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20 W 10 19
Seattle Ridge (2400′) 17 SSE 1 7

 

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.