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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, November 24th, 2023 - 7:00AM
Expires
Sat, November 25th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE at all elevations. Warm stormy weather is bringing rain up to 3,000′ in places and creating wet snow avalanche concerns for the mountains. Along the highest ridgelines snow is falling with strong winds, creating a wind slab avalanche issue. Both naturally occurring wet avalanches and wind slab avalanches are possible today.

Roof Avalanches:  Snow has been sliding off roofs during the warm weather. Be cautious of people, kids and animals straying under snow laden eaves.

SEWARD:  The Kenai Mountains are seeing similar conditions and avalanche hazards.

Special Announcements

Rain, wind, and soggy snow? It might be a good Black Friday shopping day or better yet, hit up White Friday at PowderHound in Girdwood – proceeds benefit the Friends of Chugach Avalanche Center!

Chugach State Park:  Strong winds are again impacting the Anchorage Front Range. Two days ago a skier was caught and carried in a wind slab on Flattop. The new Weekend Avalanche Outlook for this area will start Dec. 1.

Fri, November 24th, 2023
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
Sat, November 25th, 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
Sat, November 25th, 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 limited visibility we have little information as to avalanche activity over the past couple days of warm stormy weather.

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

The second wave in a series of warm storms moved in early this morning. Since midnight, almost an inch of rain has fallen in the Girdwood Valley, close to 3″ in Portage Valley and 0.4″ at Turnagain Pass. The rain/snow line looks to be somewhere between 2,500 and 3,000′. Ridgetop winds also bumped up this morning into the 20-30mph range with gusts near 60 from the east.

With such rainy weather we can expect some naturally occurring wet snow avalanches to be taking place on steep slopes and gullies. These are most likely happening in the Portage Valley, but they are also possible in the Girdwood Valley, Turnagain, down toward Seward, and anywhere rain is falling snow. If a person was to be out on a steep slope in these mushy conditions, chances are it would be easy to initiate a wet loose avalanche that could run far if the slope is long enough. Avoiding steep slopes and small steep terrain features is recommended today. Even a small wet avalanche can be quite hard to manage if it pushes us into a tree well or depression.

 

Rainfall numbers for today. Graphic courtesy of the National Weather Service Anchorage Office. You can find this and the rest of their ‘Avalanche Weather” HERE

 

A break in cloud cover during the break is storms yesterday seen from the Seattle Ridge weather station. Unfortunately, rain has made it to this station that sits at 2,400′ in elevation and looks to the south over Turnagain Pass.

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

At the upper reaches of our forecast zone (above ~3000′ or even 3,500′) winds are gusting 40-60mph from the east. At these ridgetop elevations there should be dry enough snow that newly formed wind slabs may release on their own. Not to mention being easily triggered by a human. In the right terrain, debris from a wind slab avalanche can run into wet snow and cause a wet snow avalanche, combining to produce an even larger avalanche. We see this during events similar to this one in the large avalanche paths.

Old weak layers? It’s also worth mentioning that in the high terrain there were two weak layers that we are monitoring. Weak facets near the ground above 3,500′ and buried surface hoar around a foot deep as of last week. There are a lot of unknowns with these. This storm may help to flush them out, but we will still be looking for signs they could produce avalanche down the road.

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 avalanches were occurring during the cold snap last week, and may be on the rise again with the warm conditions. Once skies clear enough to get a look around, we’ll be watching for any new glide activity.

Weather
Fri, November 24th, 2023

Yesterday:  A break between storms was seen yesterday as overcast skies and intermittent rain showers were over the region. Only 0.1 to o.4″ of rain fell through the day yet the rain/snow line rose to near 2,500′. Ridgetop winds were easterly, 10-20mph with gusts into the 30’s, before increasing after midnight last night.

Today:  Warm stormy weather is slated for today. Early this morning ridgetop winds bumped into the 20-30mph range with gusts near 60mph from the east and should remain strong through this afternoon. Rainfall has also increased with 0.5-1″ expected by the afternoon and a rain/snow line remaining near 2,500′ (5-10″ snow above 3,000′). A break in weather is expected tonight before another weaker pulse moves in tomorrow.

Tomorrow:  Strong ridgetop easterly winds and light precipitation is forecast for Saturday. Although for this round of weather, temperatures will be on the decline, which could bring snow levels down to near 1,500′. Looking ahead, cold weather is finally returning on Monday with the chance for more snow.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 37 rain 0.4 29
Summit Lake (1400′) 35 rain 0.1 18
Alyeska Mid (1700′) 36 rain o.68 26
Bear Valley – Portage (132′) 40 rain 2.8

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 29 NE 21 59
Seattle Ridge (2400′) 33 SE 15 29
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.