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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, February 20th, 2024 - 7:00AM
Expires
Wed, February 21st, 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 as a warm, wet, and windy storm impacts the region. Rain falling on snow in the mid elevations and strong wind and new snow in the high elevations will create dangerous avalanche conditions. Natural avalanches are most likely in Girdwood, Portage, and Placer Valleys and possible in Turnagain Pass where less snow is expected. Human triggered avalanches are likely in all areas. Travel in avalanche terrain is NOT recommended. 

SEWARD:  Naturally occurring large avalanches are likely due to heavy rain up to 2,500′ and snowfall above this.

Roof Avalanches: Watch for roofs with snow/ice remaining on them to continue shedding with the rain and warm temperatures.

Special Announcements

Chugach State Park: The National Weather Service has issued a Special Weather Statement for strong winds and stormy weather through Tuesday Evening. Expect avalanche danger to remain elevated during stormy and windy weather.

Friday night in Seward!
Forecaster Chat, 5-6 pm at the Community Library and Museum room
. For our friends in Seward and Moose Pass, come chat with us about the product we are producing called the “Weekend Avalanche Outlook”. We’ll also be talking about the state of the snowpack in Summit and Seward, and any other questions you have. More info Here.

Tue, February 20th, 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
Wed, February 21st, 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
Wed, February 21st, 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

Although not a lot of traffic has been out in the wet weather, a motorized Level 2 course did see a recent natural slab avalanche yesterday on the frontside of Seattle Ridge, north of the common uptrack (photo below). Crown reported to be around 1,200′ in elevation. Note how the winds have cross loaded the gullies in the photo and how the avalanche released mid-slope. The slab may have released in weak snow from January, but that is unconfirmed. Otherwise, no avalanches have been seen or reported during the past few days.

Recent natural slab avalanche mid-slope on Seattle Ridge, just north of the motorzied uptrack. Thanks to the AAS motorized Level 2 course for the photo, taken on 2.19.24.

Avalanche Problem 1
  • Wet Slab
    Wet Slab
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Slab
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

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

A warm storm ramped up last night and should peak today. Rain is falling as high as 1,500′ to 2,000′ this morning and should creep slightly higher before cooling tomorrow. Check out the precipitation graphic below. It shows around 1-1.5″ of rain in Girdwood and 2 to 3″ in Portage and Seward. This equates to 1-1.5′ and up to 3′ of snow in the high elevations respectively. Turnagain, Summit, and Moose Pass’s look to be on the drier side with only .5 to 1″ of rain (5-10″ of snow above 2,500′).

The east ridgetop winds that have been relentless for a week are currently blowing 25-40 mph with gusts near 70 and could increase even more later today. All this weather talk leaves us with increasing avalanche danger. Wet avalanches are likely at the mid and lower elevations while dry snow avalanches are likely in the higher elevations.

Wet Avalanches up to 2,500′:  Rain falling on snow up to 2,000′ and wet snow up to around 2,500′ can cause both wet loose and wet slab avalanches. Wet slabs between 1 and 3 feet deep are likely due to that layer of faceted snow from January buried 1-3′ deep. As the surface layers saturate that older weak layer can fail resulting in a wet/moist snow slab. This could have played a role in the avalanche seen yesterday on Seattle Ridge. Simply put, wet avalanche are a concern and unmanageable.

Dry Avalanches above 2,500′:  See below in Problem 2.

 


Rainfall expected at the lower elevations from 3am this morning until 3am tomorrow (Wed). Thanks to our friends at the NWS for producing these graphics. Find them HERE

Avalanche Problem 2
  • 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

Dry snow avalanches in the form of wind slabs and storm slabs are likely occurring in the higher elevations due to new snow and strong wind. This issue is most pronounced in Girdwood, Placer, and Portage Valleys where much higher snowfall amounts are expected. Check out the graphic below of the differences in snowfall expected. The higher the snowfall the more dangerous the avalanche conditions.

Persistent Slab Avalanches:  With a known layer of faceted snow buried 1-3′ deep, we can expect to see avalanches breaking deeper than our typical wind slabs per say. There is a lot of uncertainty as to how this layer will react in the higher elevations with another round of wind and snow. But either way, it’s storming out and it’s best to let the mountains do their thing before we venture into any type of avalanche terrain.

 

Snowfall expected from 3am this morning until 3am tomorrow (Wed). Thanks to our friends at the NWS for producing these graphics. Find them HERE

Weather
Tue, February 20th, 2024

Yesterday:  Cloudy skies were over the region as the next weather system headed in. Light rain began falling in the afternoon up to 1,500+’ and wet snow above this. Ridgetop winds were 5-15mph with gusts near 30 from the east during the day and increased to 25-40mph gusting 55-70mph overnight. Temperatures were warm, near 40F at 1,000′ and below and 25-30 F along ridges.

Today:  A warm, wet, and windy storm should peak today. Between .5 to 1″ of rain is expected up to 2,000, equating to 3 – 12″ of snow in the higher elevations. Whittier and Seward are expected to see closer to 2-3″ of rain and up to 24″ of wet snow in the Alpine. Ridgetop winds will remain easterly averaging 35-40mph with gusts 60-80+mph. Temperatures look to stay around

Tomorrow:  A short break is storms may bring partly clearing skies midday tomorrow before another front moves in Wednesday evening. Thankfully temperatures are expected to cool bringing snow levels down to 200-500′. From Wednesday evening to Thursday another 4-12″ of new snow could fall. Easterly ridgetop winds decrease during the day and pick back up Wednesday evening.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 34 1 0.2 83
Summit Lake (1400′) 36 0 0.1 40
Alyeska Mid (1700′) 34 2 0.65 86
Bear Valley – Portage (132′) 41 rain 2.9
Grouse Ck (700′) 36 n/a n/a 59

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25 ENE 23 66
Seattle Ridge (2400′) 28 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.