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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, March 26th, 2019 - 7:00AM
Expires
Wed, March 27th, 2019 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger is MODERATE  across the Advisory area today. Warm temperatures and direct sunshine will make triggering a wet loose avalanche possible on steep, solar aspects. Triggering a large, dangerous slab avalanche in the Alpine is also still possible.  Choose terrain carefully. Give cornices and glide cracks a wide berth. Pay attention to changing surface conditions.

PORTAGE VALLEY – Byron Glacier trail.    There is a still a chance that direct sunshine and afternoon warming could initiate wet loose avalanches that run to lower elevations or loosen cornices above this terrain. Hiking the summer trail is not recommended.  

SUMMIT LAKE (& INTERIOR EASTERN KENAI MTS):   The snowpack in this zone is shallow and has many weak layers, with the direct sunshine and warm temperatures human triggered slab avalanches remain possible in upper elevation terrain.  

SEWARD/LOST LAKE:  Similar to Turnagain –   Human triggered avalanches will be possible will today with warm temperatures and direct sunshine. Extra caution especially on steep, solar aspects in the Alpine is recommended.

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Tue, March 26th, 2019
Alpine
Above 2,500'
2 - Moderate
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.
Avalanche Problem 1
  • Wet Loose
    Wet Loose
  • 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.
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

Boom! Sunshine and springtime avalanche conditions are the name of the game now.  After almost two weeks of rain, snow, strong winds and HIGH hazard the snowpack is stabilizing with clear skies and the temperatures dropping below freezing at night. However, there are still some avalanche problems to consider today. Wet loose avalanches will be possible on steep, solar aspects in the afternoon in the Alpine as the colder drier snow becomes wet. Rocky areas are most suspect. Watch for roller balls. The wet loose avalanches may entrain more snow if they gouge into saturated lower elevation snow. After serious concerns about continued natural wet slab avalanches yesterday with all the saturated snow from the weeks of the rain, observers were happy to report a thick supportable melt-freeze crust up to around 2800′. There was also good evidence that the lower elevation snowpack is draining and overall the possibility of triggering a wet slab has significantly decreased. The surface crust may soften by the afternoon and wet loose avalanches are also possible in the lower elevations late in the day as well. Watch for punchy snow and push-a-lanche conditions in steep terrain.  

Crust @ 1500′  at 11 am became soft and punchy at 4 pm. 3-25-19. 

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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

Between 2800′- 3000′ the snowpack transitions from Spring – supportable crust over moist snow back to Winter (ish) conditions with a drier, colder, deeper snowpack. This colder snow is now getting warmed by direct sunshine and rising temperatures in the Alpine. The warming of the potential slab adds to the lingering concern of triggering an avalanche that fails on an old persistent weak layer. Finding the trigger spot in a thin area could produce a very large avalanche. Signs of instability won’t necessarily be present with this type of avalanche problem. Use good travel protocol and think about consequences if a slope does slide. It could be the 1st or 10th skier or machine on the slope that triggers the avalanche. In addition, if traveling in the Alpine look for areas that are more wind-loaded, watch for cracking and listen/feel for hollow snow indicating wind slabs in upper elevation terrain. 

CORNICES:  Cornices are very large and warm air temperatures and direct sunshine could destabilize them today. They have the potential to trigger very large avalanche on the slopes below and break way farther back than expected. Give them a wide berth. 

Snowpit @ 3100′, March 8th old snow 100 cm below the surface. 3-25-19

 

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

There were multiple glide avalanches during the past week and many glide cracks are opening around the advisory area. These are very unpredictable and not triggered by humans. Glide avalanches fail at the ground pulling out the entire season’s snowpack and could be very dangerous. The only way to avoid this hazard is by not spending time under terrain with glide cracks. 

Tincan glide avalanche and cracks, 3-25-19. 

Weather
Tue, March 26th, 2019

Yesterday: Mostly cloudy skies in the morning became mostly sunny by the afternoon. Winds were light in the morning and became calm mid day. Temperatures were in the high 30Fs to high 40Fs at sea level up to mid-elevations. At upper elevations temperatures were in the low 30Fs to mid 20Fs. Skies were mostly clear overnight and temperatures were in the 20Fs and low 30Fs. Most mid and lower elevation weather stations saw temperatures dip below freezing.  

Today: Skies are forecast to be mostly clear and sunny. Winds will be light and northerly. Temperatures will rise by the afternoon to the low 30Fs at upper elevations and the mid to high 40Fs at lower elevations. Overnight should be mostly clear and temperatures should dip down again below freezing.  

Tomorrow: The weather looks to be very similar to today with slightly higher temperatures and a chance of more overnight cloud cover. Sunshine is in the forecast into next week as the high pressure parks over the area.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 35   0   0   71  
Summit Lake (1400′)  32     0   0   24  
Alyeska Mid (1700′)  34      0      0     65  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26   W   5   17  
Seattle Ridge (2400′)  31     E     3   10  
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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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