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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, November 26th, 2023 - 7:00AM
Expires
Mon, November 27th, 2023 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2500′. We have very limited information from the alpine due to a series of warm, wet storms impacting the forecast area this week. Human triggered avalanches 1-2′ deep within the new storm snow are likely at upper elevations today. Below 2500′ the avalanche danger is MODERATE. Rain and wet snow have been falling at these elevations, which make wet and glide avalanches our primary concern.

Roof Avalanches: Until the temperatures drop again we continue to be concerned about the potential for roof avalanches.

SEWARD: Today’s storm is expected to favor the Seward area with heavier precipitation, so avalanche danger will likely increase at upper elevations.

Special Announcements

Chugach State Park: Periods of heavy precipitation are expected in the Anchorage Front Range today. Be on the lookout for fresh wind slabs and check how well the new snow is sticking to the old snow surface.

New weekend outlook products:  Starting Friday, Dec. 1, we will begin issuing Weekend Avalanche Outlooks for Chugach State Park, the Summit Lake/Central Kenai zone, and the Seward/Southern Kenai zone. These Outlook products will be published Friday evenings and will provide avalanche information for these three new areas for us.

Sun, November 26th, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Mon, November 27th, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Mon, November 27th, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
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

With the occasional breaks in cloud cover yesterday we could see a lot of new wet loose and glide avalanche activity. Penguin Ridge near Girdwood had widespread glide releases that started from higher elevations and ran down into treeline elevations.

Wet loose and glide avalanches releasing naturally from Penguin Ridge near Girdwood. Photo 11.25.23

Glide release from peak 4940′ near the Johnson Pass Trailhead on the west side of the road. Photo 11.25.23

Avalanche Problem 1
  • Wet Loose
    Wet Loose
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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

We’re looking at another day of wet and unsettled weather today, with 0.25 – 0.5″ of water falling as rain and snow throughout the day. The precipitation should be heavier in Girdwood and Portage compared to Turnagain Pass. Rain line will be around 1500-2000′ today.

Below 2000′ wet loose and glide avalanches are the primary avalanche problems today. After 4 days of wet and warm weather the surface of the snowpack is saturated at these lower elevations and it will be easy to initiate a wet loose avalanche in steeper terrain. This type of avalanche starts from a single point and entrains more and more snow as it flows downhill. On larger terrain features wet loose avalanches can run long distances and be quite destructive. To avoid this issue be aware if you travel on or underneath steep terrain features and try not to travel directly above your partners.

Large wet loose avalanches failing naturally in steep terrain on Bird Ridge and entraining more snow as it fans out while flowing downhill. 11.25.23

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

It’s been awhile since we got any information from higher elevations, so we don’t really know what is going on up there. However, with the consistent snowfall and windy conditions during this series of storm systems over the past several days you can expect a few feet of new snow and plenty of fresh wind slabs. If you decide to brave the whiteout at upper elevations keep an eye out for wind loaded terrain features that could easily produce wind slabs 1-2′ deep. To assess wind slab conditions we recommend using small wind loaded terrain features to test how reactive the new snow is to the weight of a skier or rider before jumping onto larger terrain.

View looking up into Tincan Common bowl yesterday from treeline at 2200′. 11.25.23

Additional Concern
  • Glide Avalanches
    Glide Avalanches
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.
More info at Avalanche.org

Glide cracks have been opening up across the forecast area and many glide avalanches have released in the past few days. These can produce large and destructive avalanches, so we recommend avoiding spending time underneath glide cracks. With the limited visibility over the past few days it can be difficult to see whether there is a glide crack above you, so we recommend sticking to familiar routes and minimizing the amount of steep terrain overhead.

Weather
Sun, November 26th, 2023

Yesterday: Warm temperatures persisted yesterday hovering around 35-40 F at lower elevations and 25-30 F at upper elevations. Rain line was roughly 2000′ yesterday, with only 0.2″ of SWE falling in Turnagain Pass, 0.6″ in Girdwood, and 1.8″ in Portage. Winds averaged 10-20 mph throughout the day and increased slightly overnight with gusts up to 40 mph. Cloud cover was mostly overcast and obscured with occasional pockets of broken skies moving though the forecast area.

Today: Precipitation is expected to continue on and off throughout the day today. The heaviest rain and snowfall should be this morning, with lighter precipitation rates throughout the day before ramping up again overnight tonight. Rain line is expected to remain at 1500 – 2000′ today. Girdwood and Portage continue to be favored for higher precipitation totals during the day, with about 0.5″ of SWE expected in Girdwood, 1″ of SWE expected in Portage, while Turnagain Pass should be closer to 0.25″ of SWE today. Wind speeds should peak around 8am this morning with averages around 20 mph and gusts to 40 mph before shifting to the south and decreasing to 10-15 mph with gusts to 25 for the rest of the day today.

Tomorrow: Another low pressure system will move through our area Sunday night into Monday, bringing 0.25-0.5″ of SWE. Rain line is expected to decrease throughout the day Monday, dropping from 2000′ Sunday evening to about 200′ by Monday afternoon. Wind speeds will increase again with averages of 15-25 mph and gusts to 35 mph.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 34 0 0.2 28
Summit Lake (1400′) 34 0 0 17
Alyeska Mid (1700′) 35 0 0.6 22
Bear Valley – Portage (132′) 39 0 1.8 –

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 27 ENE 16 38
Seattle Ridge (2400′) 30 ESE 6 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.
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