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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, January 5th, 2024 - 7:00AM
Expires
Sat, January 6th, 2024 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′. Human triggered avalanches releasing 2-3′ deep at the base of the storm snow from the past 48 hours remain possible due a weak layer at the old snow surface. Wind slabs forming along upper elevation ridgelines could cause natural or human triggered avalanches 1-2′ deep in exposed areas. In addition, glide cracks are releasing frequently in recent days which can cause very large and destructive avalanches. We recommend a cautious approach to entering avalanche terrain today and if you want to avoid these hazards stick to lower angle terrain that is not underneath a glide crack. Below 1000′ the avalanche danger is MODERATE.

SEWARD & LOST LAKE: The mountains around Seward are expected to receive 8-12″+ of snowfall today, significantly more than the rest of the region, which will rapidly increase avalanche danger. Natural and human triggered avalanches will be very likely if this amount of new snow falls on top of the existing storm snow from this week.

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.

Fri, January 5th, 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
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
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
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

Widespread natural avalanches were observed yesterday that likely released sometime during the storm on Wednesday. The most notable avalanche activity was in the Placer River area where the storm dropped 2.5-3.5′ of new snow and therefore the storm slab avalanches were deeper and more reactive. One human triggered avalanche was reported from this area, caused by a snowmachiner sidehilling across a small slope. In addition, there was a glide avalanche on the SE aspect of Seattle Ridge that released since the storm ended on Wednesday.

Zoom in on this photo to see the widespread avalanche activity on the mid-elevation convex terrain features. Photo Jeff Dennis 1.4.2024

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Aspect/Elevation
  • 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.

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 2-3′ of new snow that fell in the forecast area from Tuesday through Thursday is not bonding to the old snow surface as well as we might hope. Observations from across the forecast area (Placer, Sunburst, Cornbiscuit, Lipps) reported storm slab and wind slab avalanche activity on Wednesday and Thursday, which seem to be releasing at the interface with the old snow surface. Due to the very cold temperatures last week that old snow surface is made up of a mix of weak snow grains, including surface hoar and near surface facets. Natural and human triggered avalanches 1-3′ deep will remain possible today due to the weak interface with the old snow and the potential for active wind loading at upper elevations.

The weak old snow surface buried 2-3′ deep could cause avalanches to release on lower angle slopes than typical. We recommend a cautious approach to travelling in avalanche terrain today and selecting terrain features that minimize your exposure to large slopes with consequential runouts. Jumping or riding on small, steep test slopes can be very useful to determine how well the new snow is bonded to the old surface. However, in areas where the new snow is deeper, like Placer Valley, it may be harder to get feedback from the snowpack due to the depth of the potential weak layer.

Wind Slab avalanches are likely today due to sustained moderate winds expected throughout the day. Yesterday we observed widespread wind loading along upper elevation ridgelines and there was still plenty of soft snow to be blown around. Keep an eye out for any active transport, shooting cracks, or hollow feeling snow along ridgelines to identify areas harboring wind slabs. It is possible that a small wind slab could trigger a larger avalanche on the old snow surface.

Snowpack structure in the treeline elevation band on Sunburst showing the weak layer at the old snow surface. Photo 1.4.2024

 

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

In the past 10 days or so there have been a lot of glide avalanches releasing, including in popular travel locations on the skiers side and motorized side of Turnagain Pass. One new glide avalanche released on the SE aspect of Seattle Ridge during or just after the storm on Wednesday. With a blanket of new snow laid across the landscape it is a little easier to tell which glide cracks have been recently active by looking for freshly exposed bare ground. Currently there are a lot of glide cracks located in inconvenient spots, like above the Seattle Creek uptrack, which make it difficult to avoid them entirely. We recommend being aware of glide cracks in your vicinity and trying to minimize the amount of time you spend underneath.

Recent glide release on a south aspect along Seattle Ridge. Photo Mike Janes 1.4.2024

Weather
Fri, January 5th, 2024

Yesterday: Overcast to broken cloud cover for most of the day, with snow showers starting in the afternoon and light rain at lower elevations. Overnight another pulse of precipitation moved through the area, leaving about 0.5″ of SWE (4-6″ snow) in Girdwood and Turnagain Pass and closer to 1″ of SWE (10-12″ snow) in Portage and Placer. Temperatures were in the mid to high 20s F above treeline and in the 30s F below treeline, with rain line at approximately 500′. Winds were moderate during the day, averaging 5-15 mph with gusts to 30 mph out of the east, and increased slightly overnight, with averages of 15-30 mph and gusts to 55 mph out of the east.

Today: Snowfall is expected to taper off this morning, but lingering showers could bring another 1-3″ during the day today. Temperatures will remain in the mid to upper 20s F at upper elevations and low 30s F at lower elevations with rain line in the 600-800′ range. Winds will remain moderate throughout the day, with averages of 15-25 mph and gusts of 35 mph+ out of the southeast. Cloud cover will most likely remain over the area although we could see some breaks in the clouds providing periods of better visibility.

Tomorrow: Another storm system will approach the forecast area tomorrow, with snowfall expected to start again around 12-3pm on Saturday. Winds will start out light in the morning averaging 5-15 mph out of the southeast, but will increase sharply ahead of the storm with averages bumping up to 30-40 mph out of the east by the Saturday evening. The most intense period of snowfall is expected to be Sunday morning. Only a few inches of snow are expected Saturday night, with up to another foot of snow possible on Sunday. Rain line should remain in the 500-600′ range.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 5 0.4 88
Summit Lake (1400′) 28 0 0.0 N/A
Alyeska Mid (1700′) 31 6 0.6 79
Bear Valley – Portage (132′) 36 rain 1.02
Grouse Ck – Seward (700′) 34 7 0.8 53

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22 ENE 16 55
Seattle Ridge (2400′) 26 SE 8 19
Observations
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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.