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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, April 11th, 2024 - 7:00AM
Expires
Fri, April 12th, 2024 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′. More wind and snow is on the way today, and the snow from Tuesday’s storm may still be reactive as this next loading event begins. It will be easy to trigger an avalanche up to 1 to 2 feet deep on freshly wind loaded slopes today, and larger avalanches failing below Tuesday’s storm remain a concern. Be on the lookout for increasing danger through the day, and take the time to carefully evaluate the upper snowpack before entering steep terrain. The danger is MODERATE below 1000′, where the same avalanche concerns exist but lower snow totals and lighter winds will make avalanches generally smaller and a little less likely.

SEWARD/LOST LAKE: This storm is arriving from the south and is expected to favor the Seward and Lost Lake areas with 6-10″ snow likely by tonight. Avalanche danger will increase through the day, with natural and human-triggered avalanches likely by tonight.

Special Announcements

Avalanche Center End of Season Operations: This is the final week of daily 7am avalanche forecasts. Beginning April 15 we will forecast 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 11th, 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 12th, 2024
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
Fri, April 12th, 2024
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

There were several human-triggered avalanches yesterday as the skies cleared and people got out immediately after the storm. This includes multiple avalanches that were triggered remotely from slopes connected to steeper terrain. People were triggering avalanches on both sides of the highway at Turnagain pass, with observed activity on Tincan, Cornbiscuit, and Main Bowl. These avalanches were around a foot deep on average, 50-200′ wide, and were failing at the interface between Tuesday’s storm snow and a previous crust.

Remotely-triggered avalanche on Cornbiscuit. Photo: Todd Kelsey, 04.10.2024

Multiple skier-triggered avalanches on Widowmaker in Main Bowl on the back side of Seattle Ridge. 04.11.2024

Avalanche Problem 1
  • 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

Another round of active weather is arriving today, and we’re expecting avalanche conditions to remain dangerous as wind and snowfall pick up through the day. The ‘Storm Slab’ icon in today’s forecast represents a broad range of avalanches that we expect to encounter as the weather picks up, which may be larger than you would expect with only a few inches of snow in the forecast. The likelihood of wind slab avalanches will increase as winds ramp up to 20-40 mph, gusting 30-50 mph. These may be up to 1 to 2′ deep, and will become larger and more likely at upper elevations.

This new loading event arrives as we are still assessing the interface from Tuesday’s storm. We saw multiple avalanches failing on that storm interface yesterday, and it is unclear how long that layer will remain reactive. What we do know is that the storm buried a combination of weak surfaces including facets, surface hoar, and crusts – none of these are very confidence-inspiring. This interface should be treated as guilty until proven innocent for now, and steep terrain should be approached with caution. The layer is around 6-10″ deep at Turnagain Pass, and 1 to 2 feet deep in Girdwood and closer to the coast.

Natural avalanches near the Seattle Headwall. The likelihood of similar avalanches will increase today as the weather picks up. 04.10.2024

 

Weather
Thu, April 11th, 2024

Yesterday: Skies were partly to mostly sunny for most of the advisory area, with lingering valley and upper-level clouds in some locations. Winds were light out of the east, averaging 5 to 10 mph. Temperatures got up to the mid 20s F at upper elevations and upper 30s to low 40s F closer to sea level. Overnight lows were in the low 20s to 30 F.

Today: Active weather passes through today and tonight, with strong southeasterly winds and a few inches of snow on the way. Coastal areas may see 3-6” snow during the day today, with 1-3” expected for Girdwood, Turnagain Pass, and Summit Lake. We may see some rain at sea level, but it shouldn’t go higher than about 100 feet. Winds are looking to be strong out of the southeast at 20 to 40 mph with gusts of 30 to 50 mph. Skies will be partly to mostly cloudy. High temperatures should be in the mid 20s to low 30s F, with lows in the low 20s to 30 F.

Tomorrow: Snowfall is expected to continue through tonight, with another 2 to 5” snow likely for most locations before the storm passes early tomorrow morning. Winds will switch westerly as the storm passes, backing down to 5 to 10 mph with gusts around 10 to 15 mph. High temperatures should be in the mid 20s to mid 30s F, with lows in the low to mid 20s F. Skies are expected to remain mostly cloudy.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28 0 0 99
Summit Lake (1400′) 25 0 0 46
Alyeska Mid (1700′) 31 0 0 120
Bear Valley – Portage (132′) 34 0 0.04
Grouse Ck (700′) 29 0 0 76

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21 ENE 7 43
Seattle Ridge (2400′) 25 SE 3 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.