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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, April 18th, 2024 - 7:00AM
Expires
Fri, April 19th, 2024 - 7:00AM
Forecaster
Daniel Krueger
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′ today. At mid and upper elevations strong winds overnight blew snow into fresh wind slabs 1′ deep or deeper. These may become larger as strong winds continue all day, releasing naturally, and will be easy for person to trigger. The avalanche danger is MODERATE below 1000′ where wet loose avalanches are possible due to above freezing temperatures overnight.

SEWARD/LOST LAKE: Up to 10″ of new snow and rain (1″ SWE) is forecast in the Seward and Lost Lake zones which may increase the size and chance of natural and human triggered wind slab avalanches 1 to 2′ deep. Depending on how much snow falls, storm slabs could also release naturally or be easy to trigger. Wet loose avalanches could be possible on slopes affected by rain and above freezing temperatures as the rain line is expected to reach 1700′ today.

FRIDAY – AVALANCHE OUTLOOK: Strong east winds are expected to continue into Friday afternoon making natural wind slab avalanches possible and likely for a person to trigger. Partly sunny skies and temperatures forecast in the low 40’s could increase the chance of wet loose avalanches on east, south, and west slopes.

Special Announcements

Avalanche Center End of Season Operations: We are continuing to issue forecasts on Tuesday, Thursday, Saturday, and Sunday mornings. For the non-forecast days we will give an avalanche outlook on the day prior. The final forecast for the season will be April 28.

Thu, April 18th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Fri, April 19th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Fri, April 19th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
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 observations there have been no avalanches reported since Monday when a glide avalanche was reported on Penguin Ridge. On Sunday April 14, small wet loose avalanches were seen on Sunburst’s steep south facing slopes.

Avalanche Problem 1
  • 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 looks like this storm brought more wind than snow. Strong northeast winds pounded Turnagain Pass for 11 hours with winds averaging 50+ mph overnight and gusting around 100 mph! This likely blew new and old snow from mid to upper elevations into touchy wind slabs 1′ deep that will continue to get larger throughout the day. These may release naturally and will be easy trigger. They could be hard wind slabs which may allow someone to get way out on to a slope before they trigger an avalanche. In some places they may be forming over a crust which is a great bed surface for snow to slide on. This problem can be found at upper AND mid elevations along ridgelines, rollovers, in cross loaded gullies and in the trees. Look out for shooting cracks, firm snow over soft snow, and test small slopes to see if you can safely trigger small avalanches. While we recommend a conservative approach into avalanche terrain, steep wind loaded slopes will be easy to trigger, and it may be hard to find enjoyable conditions today.

Strong northeast winds recorded at Sunburst. In Girdwood and Portage strong winds were also reported.

Avalanche Problem 2
  • 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

In Turnagain pass, temperatures are already above freezing and are expected to increase throughout the day. Combined with light rain, wet loose avalanches may be possible. This problem could increase if the rain picks up or if the sun pokes out and temperatures rise in the afternoon. These can be found on all slopes, especially on steep, east, south, west aspects. If you are wallowing in wet snow, it may be a good time to turn around or choose shaded slopes.

 

Additional Concern
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

It has been over six days since a human triggered an avalanche on a layer of facets and surface hoar buried 1 to 2′ deep. We saw many tracks on all aspects on Tuesday with no signs of slab avalanche activity. Usually this is telling us there is a small chance of triggering an avalanche on this layer. While we do not feel it is likely to trigger one of these avalanches, consider this potential if you travel into steep consequential terrain.

Weather
Thu, April 18th, 2024

Yesterday: A storm stationed southwest of Kodiak brought cloudy skies and strong winds from the northeast across the Kenai Peninsula. Winds on Sunburst averaged 80 mph with 109 mph recorded overnight! With a trace of snow reported it appears most of the precipitation missed us.

Today: Cloudy skies in the morning may break up for a little sunshine in the late afternoon. East winds look to average 10 to 20 mph with ridgetops gusting 30 to 40 mph. Up to 5″ of new snow is possible that should dissipate in the afternoon as temperatures may reach the high 30s.

Tomorrow: Partly sunny skies may prevail with ridgetop winds from the east averaging 10 to 15 mph with 30 mph gusts. Little to no snow is expected as the freezing line may approach 2,200ft. Temperatures look to range between 30F and 45 F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 35 0 0.1 96″
Summit Lake (1400′) 39 0 0 45″
Alyeska Mid (1700′) 36 0 0 111″
Bear Valley – Portage (132′) 42 0 0.1
Grouse Ck (700′) 36 0 0.1 72″

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25 ENE 53 109
Seattle Ridge (2400′) 27 SE 21 42
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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.