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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, January 3rd, 2024 - 7:00AM
Expires
Thu, January 4th, 2024 - 7:00AM
Forecaster
Wendy Wagner
High Avalanche Danger
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

The avalanche danger is rising to HIGH today due to a warm storm over the region. Heavy snowfall and strong east winds are expected to cause avalanches to release on their own. These storm snow avalanches could be large enough to send debris into the lower elevations where it’s raining. Travel in avalanche terrain in NOT recommended. 

SEWARD/LOST LAKE:  Heavy rain and snow is falling here as well and natural avalanches are likely to occur.

Roof Avalanches:  Rain is falling below 1,200′ and may cause snow-laden roofs to shed their snow. Be aware of kids, dogs, vehicles, etc that might be under roofs that could avalanche.

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.

Wed, January 3rd, 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
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'
3 - Considerable
Avalanche risk
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'
3 - Considerable
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

Over the past week, prior to the storm over us currently, the only avalanche activity seen has been glide avalanches. Glide cracks have been releasing into avalanches on a regular basis in high use areas.

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

Warm and stormy weather moved in yesterday, is peaking today, and should head out tonight. The rain/snow line crept up to 1,200′, give or take, last night and should remain here through the day. Turnagain Pass has seen ~0.5″ of rain at the road and 5-6″ of snow above treeline. Girdwood and Portage Valleys have been wetter with closer to 1″ of rain below 1,000′ equating to roughly 10″ of snow at the higher elevations. To the south, Summit Lake has only seen a couple inches of snow and Seward around 0.5″ of rain. Ridgetop winds have been easterly, 25-35mph, with gusts near 70. These strong winds are forecast to continue through today. An additional 0.5-1″ of rain is forecast for Girdwood and Turnagain Pass below 1,200′, 8-12″ of snow above this. Portage and Placer Valleys are likely to see double these amounts. All this said, stormy weather = avalanche danger.

Naturally occurring storm snow avalanches will be the main concern today. At the mid and upper elevations where it’s snowing and blowing, we can expect natural cornice falls and wind slab avalanches 1-2+’ thick. In areas sheltered by the winds, storm snow avalanches are possible where over a foot of new snow has accumulated. Keep in mind the old snow surface was quite weak, composed of sugary near surface facets and some surface hoar. Even the harder wind effected snow along ridgelines was reported to have been faceting (weakening) before the storm. How well the new snow bonds with the old surface will be our main question for today as well as moving forward. At this point, we can expect the new snow will be very touchy and easy to avalanche.

At the lower elevations, wet snow avalanches are a concern on steep terrain features. If the soggy weather doesn’t hinder our excitement for heading into the backcountry, then it’ll be important to steer clear of slopes over 30 degrees and stay well away from steep slopes overhead.

 

Snowfall totals forecast for 3am this morning through 3am tomorrow. Graphics found on the ‘Avalanche Weather’  page from the NWS Anchorage office.

 

Photo of what the snow surface looked like in the mid elevations at Turnagain Pass (Cornbiscuit). Several inches of loose faceting snow existed before the storm. 12.28.23.

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

Although the storm is stealing the show today, we can assume glide cracks are continuing to release into full-depth avalanches throughout the region. For over a week now, this type of avalanche has occurred on a daily basis, and some in well-traveled areas. It is one more reason to avoid avalanche terrain today. Once the storm moves out, we’ll again be looking for these cracks and limiting time under them.

Weather
Wed, January 3rd, 2024

Yesterday:  Warm and stormy weather moved in yesterday with cloudy skies, strong winds, and light precipitation. Ridgetop winds were easterly 25-35mph with gusts 60-70mph. Light snow turned to rain up to 1,000-1,300′ overnight. As of 6am this morning roughly 4-6″ of snow has fallen in the higher elevations with 0.5″ of rain in the lower elevations.

Today:  The storm peaks today with an additional 8-12″ of snow in the high terrain and 0.5-1″ of rain below 1,200′. The rain/snow line looks to remain in the 1,000′-1,300′ band with 40F temps near sea level. Ridgetop winds are expected to stay in the 25-35 mph range with gusts near 60. Temperatures in the Alpine should stay in the mid 20’sF.

Tomorrow:  As the storm tapers, mostly cloudy skies, light snowfall (1-2″), and moderate east winds are expected for Thursday. Another system is headed in Thursday night into Friday, which could be slightly cooler and bring another few inches or so of snow. Stay tuned.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 4 0.5 77
Summit Lake (1400′) 30 1 0.1 N/A
Alyeska Mid (1700′) 31 4 0.5 70
Bear Valley – Portage (132′) 38 rain 0.9
Grouse Ck – Seward (700′) 34 rain 0.4 47

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22 NE 37 74
Seattle Ridge (2400′) 23 SE 14 31
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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.