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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, January 4th, 2024 - 7:00AM
Expires
Fri, January 5th, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

As yesterday’s storm moves out the avalanche danger is dropping to CONSIDERABLE at the mid and upper elevations and MODERATE near sea level. This is the most dangerous time for human triggered avalanches. Although a few natural storm snow avalanches could occur today, more concerning is how easy it might be for people to trigger avalanches. These would be 1-3′ deep slabs composed of the new snow and they could be triggered remotely (meaning from the side, top, or bottom of a slope).

*Careful route-finding and a cautious mindset is key today. Sticking to slopes 30 degrees or less with nothing steeper above is a good way to enjoy the new snow and avoid avalanche issues.

Special Announcements

The National Weather Service has issued a Special Weather Statement regarding snowfall along the Seward Highway corridor this afternoon through Friday.

Thu, January 4th, 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
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
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
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

Not much is known yet regarding the extent of natural avalanches from the storm yesterday. Yet, we can assume there was some degree of storm snow avalanche activity. We hope to get some eyes on the slopes today if skies allow.

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

Dangerous avalanche conditions may exist today. We have yet to find out how well the new snow has bonded to the old surface. With 1-2′ of new snow in our popular zones, avalanches can easily be large enough to bury a person.

Yesterday’s warm and windy storm added a healthy dose of snow to the higher elevations (1-3 feet). Rain fell as high as 1,500′ in places and around 1,200′ at Turnagain Pass. The storm is moving out today, yet another pulse of wind and 2-6″ of snow is slated for tonight. Temperatures have cooled slightly this morning and any lingering snow showers should make it to 500′ before turning to rain. With a break in weather today, save for some gusty east winds along the ridgetops, our main avalanche concerns will be related to the new snow that has fallen since Tuesday afternoon.

Storm Total ESTIMATES for upper elevations (new snow since Tuesday afternoon):
Girdwood: 20-30″ snow (1.5-3″ of water equivalent)
Portage/Placer:  30-40″ snow (3-4″ water)
Turnagain Pass:  12-24″ snow (1-2″ water)
Summit Lake:  1-3″ snow (0.1-0.2″ water)

Storm Slab Avalanches:  Triggering a slab avalanche that breaks at the new/old snow interface could be very easy. The new snow is between 1-2′ in general and maybe up to 3′ deep in some areas. It is sitting on a mix of loose faceted snow, surface hoar, and wind affected snow. How well it’s bonding to these old surfaces is questionable and why we need to be extra cautious. Watching for recent avalanches, shooting cracks, or any whumpfing/collapsing signs will be critical.

Wind Slab Avalanches:  Wind slabs are a sure bet in exposed areas, along ridgelines, and in cross-loaded gullies. These can be several feet deep and due to the storm just wrapping up, very easy to trigger. Another reason to stick to the low angle terrain.

Cornices:  After 2 days of strong winds and sticky wet snow, we can bet cornices have grown in size. If the weather clears enough to get to ridgelines, watch for these to be easy to fail. If a chunk breaks off, it could trigger an avalanche below.

 

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

It will be interesting to see if any glide cracks released during the storm yesterday. It may be tough to tell. There are so many littered about it can be hard to discern what glide avalanches are new what ones are old. Either way, we can assume glide cracks are continuing to release into full-depth avalanches throughout the region. Once the skies clear enough, we’ll again be looking for these cracks and limiting time under them.

Weather
Thu, January 4th, 2024

Yesterday:  Warm and stormy weather was over the region yesterday. Precipitation totals for the past 24-hours ranged from 1-3″ with the highest amount in Portage Valley (1.3″ at Center Ridge snotel on Turnagain Pass). This equates to 1-3 feet of snow in the higher elevations. Rain/snow line has been 1,000-1,300′. Ridgetop winds were from the east 25-35mph with gusts 50-60mph. Temperatures have been in the upper 30’sF at sea level and mid 20’s along ridgetops.

Today:  A short break in weather is forecast today, Thursday, before another pulse of wind and snow pushes in tonight. For the daylight hours, mostly cloudy skies with periods of light rain below 500′ and scattered snow showers above are expected. Ridgetop winds should stay easterly 10-20mph with gusts near 30mph. Tonight, 2-6″ of snow is forecast with winds bumping up to the 20’s gusting near 40mph. Temperatures look to cool slightly, into the mid 30’sF at sea level and low 20’sF on the high peaks.

Tomorrow:  The weather front moving through tonight looks to move out tomorrow. For Friday, we can expect mostly cloudy skies, ridgetop winds 10-20 from the east and possibly some lingering showers. This break in storms should last into Saturday before more active weather returns on Sunday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 13 1.3 88
Summit Lake (1400′) 32 1 0.1 N/A
Alyeska Mid (1700′) 32 5-10 1.2 73
Bear Valley – Portage (132′) 37 rain 3.1
Grouse Ck – Seward (700′) 34 1 0.2 46

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24 NE 27 58
Seattle Ridge (2400′) 27 SE 11 30
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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.