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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, April 9th, 2019 - 7:00AM
Expires
Wed, April 10th, 2019 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE  at all elevations. In the mid-elevations, glide avalanches continue to release sporadically and are creating a dangerous and unpredictable hazard. Limit any travel under glide cracks. Additionally, wet loose sluffs are possible on saturated steep slopes below 2,000′. In the Alpine, watch for areas with new wind-drifted snow where small wind slabs may be triggered on steep shaded slopes. And as always, give cornices a very wide berth.

GIRDWOOD VALLEY:   Between 4-6″ of new snow has fallen in the higher elevations of Girdwood Valley. Wind slabs up to 10″ thick along with dry/moist sluffs could be found on steeper slopes in the Alpine.  

PORTAGE VALLEY:   Summer trails with avalanche terrain overhead, such as Byron Glacier Trail, are not recommended due to the possibility of an avalanche or cornice fall sending debris over the trail.

Special Announcements
Tue, April 9th, 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
  • Glide Avalanches
    Glide Avalanches
  • 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.
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

Glide avalanches continue to be the most concerning avalanche problem for anyone traveling in avalanche terrain. Glide cracks litter the slopes and could release into an avalanche at anytime. Cracks are predominatly opening at elevations below 3,000′ and on E, S and W aspects. They are not triggered by people and are very unpredictable and destructive to anything in their path. The last known glide crack to release into an avalanche was Sunday morning, just south of Turnagain Pass near the Hope Wye cutoff. What we can do is keep our eyes open and limit/avoid traveling under cracks (example photo below). This may take some creative route planning in places, but it could be well worth it if a crack decides to release in your vicinity.

WET LOOSE:  Triggering a wet loose avalanche (sluff) on steep slopes that did not freeze overnight is possible. This will be most likely on slopes below 2,000′ that have been soaked by rain and remain wet and unsupportable. 
 

Glide cracks on Tincan under Common Bowl. 

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
  • 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.
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 may be wet and raining down low, but it’s still relatively dry up high. Above 2,500′, anywhere from 1-6″ of new snow fell over the region yesterday (favoring Girdwood) which was added to the 3-6″ of new snow from over the weekend. Plug in moderate easterly ridgetop winds and we can expect 4-10″ thick wind slab on leeward facing slopes. Shaded aspects will be the most touchy as wind slabs are sitting on weak older snow (facets/buried surface hoar). One of these slabs was found on the North Chutes on Tincan Sunday (photo below). Keep a lookout for wind deposited snow, fresh drifts and watch for cracking around your skis/board or machine. Even a small wind slab can be a problem in steep rocky terrain.

Small, shallow skier triggered wind slab on one of Tincan’s north facing chutes on Sunday. (Photo Adam Baxter)

 

CORNICES: Cornices remain very large along some ridgelines in the Alpine. These cornices can break suddenly and pull back onto flat ground above a slope. Give them a wide berth and avoid travel directly below them.

South of Turnagain in Summit Lake and areas in the interior Kenai Peninsula still posses a variety of old weak layers within the snow pack. Be aware of a variety of avalanche conditions ranging from small isolated wind slabs to wet loose. Triggering a persistent slab 2-3′ deep is becoming an outlier at this point, but the poor snowpack structure is worth noting if headed to Summit.  

Todd’s Bowl and the North facing Chutes of Tincan at Turnagain Pass. Winter remains at these higher elevations. 

Weather
Tue, April 9th, 2019

Yesterday:   Cloudy skies with light rain fell up to 2,000′ over the region. Girdwood picked up just under 1/2 an inch of rain, while Turnagain Pass saw around a tenth of an inch in the past 24-hours; this equates to 4-6″ of snow above 2,500′ and 1-2″ respectively. Ridgetop winds have been moderate, averaging 10-20mph with gusts near 40mph from the east. Temperatures climbed to the upper 20’sF at 4,000′ and the  mid 40’sF at 1,000′ before dropping to the mid 20’sF at 4,000′ and the mid 30’sF at 1,000′.  

Today:   Mostly cloudy skies, with a few breaks in cloud cover, are in store today as a weak low pressure spins in the Eastern Gulf. A few raindrops may fall up to 2,000′ with flurries above this in favored areas. No measureable precipitation is expected. Ridgetop winds should remain moderate from the east in the 10-20mph range with gusts into the 30’s at times. Temperatures will be on a slow decline as cooler air moves in and highs near 40F are expected at 1,000′, while ridgetops remain in the mid 20’sF.  

Tomorrow:   A brief break between systems should bring partly cloudy skies, mild temperatures and light easterly winds for Wednesday. A powerful front is forecast to hit the region Thursday bringing heavy rain, 4-10″ of snow above 2,000′ and 50-70mph winds. Stay tuned!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 37   rain   0.1   63  
Summit Lake (1400′) 37    0 0   19  
Alyeska Mid (1700′) 35   0.5   0.42   57  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 27   NE   14   39  
Seattle Ridge (2400′) 31   SE   11   20  
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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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