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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, April 3rd, 2024 - 7:00AM
Expires
Thu, April 4th, 2024 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger remains CONSIDERABLE above 1000′. There were four large human-triggered avalanches yesterday, all failing at the interface between this week’s snow and an older crust. It is likely we will be able to trigger similar avalanches today- up to 2 to 4′ deep and several hundred feet wide. Along with these bigger avalanches, it will also be important to pay attention to loose snow avalanches. The avalanche danger is MODERATE below 1000′ where the same hazards exist but are smaller and a little less likely.

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Wed, April 3rd, 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
Thu, April 4th, 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
Thu, April 4th, 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

There were multiple human-triggered avalanches yesterday. This includes three remotely triggered avalanches in Main Bowl on the back side of Seattle Ridge, one skier-triggered avalanche on Notch Mtn. near Girdwood, and one snowmachine-triggered wind slab just outside of our advisory area near Whittier. All of these failed at the interface between this week’s storm snow and the older crust. The avalanches were up to 2 to 4′ deep and several hundred feet wide. One snowmachine was pushed by moving debris near the bottom of one of the avalanches, but nobody was buried in any of the avalanches.

This remotely-triggered avalanche near Main Bowl was the largest avalanche seen yesterday. Photo: Brandon Wilson, 04.02.2024

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

Well, we don’t always get clear signs when conditions are dangerous, but yesterday was about as clear as it gets. We received reports of four large human-triggered avalanches failing at the interface between this week’s storm snow and an older crust, and are expecting it is likely we’d be able to trigger similar avalanches today. It is unclear whether these avalanches are failing on a low-density storm snow layer just above the crust, or if there is some kind of persistent weak layer involved that will be giving us problems for days or weeks to come. This will be our main focus over the next few days, but for now we should use yesterday as a free warning to treat steep terrain with caution. These avalanches were up to 2-4′ deep and several hundred feet wide, plenty big enough to have serious consequences.

In addition to these bigger avalanches, loose snow avalanches are also likely today. Skiers observed dry loose avalanches (sluffs) in steep north-facing terrain yesterday on Cornbiscuit, and similar activity should be expected today. If we end up seeing sun later in the day, the chances for wet loose avalanches in steep terrain on the south half of the compass will increase. The first places we tend to see these are on steep slopes with rocks or trees, where the snow heats up the fastest. They may also be triggered by chunks of falling cornices, which will also become more likely if things warm up later in the day.

This avalanche on Main Bowl’s Widwomaker was triggered remotely from the ridge. There is a good chance we could trigger a similar avalanche today. Photo shared anonymously, 04.02.2024.

Loose snow avalanches in steep south-facing terrain off Magnum Ridge. These were most likely triggered by small pieces breaking off the cornice and falling onto the slope. Similar avalanches should be expected today if the sun comes out. Photo: Nolan Dumont, 04.02.2024.

Weather
Wed, April 3rd, 2024

Yesterday: Skies were partly to mostly cloudy with westerly winds that were light for most areas, averaging 5 to 10 mph gusting up to 15 mph. Winds were stronger along major terrain gaps like Portage, Whittier, and Seward. High temperatures were in the mid 20s to low 30s F with lows in the teens F. We did not record any precipitiation.

Today: It is looking like we will have another day of cloudy weather, with partly to mostly cloudy skies and some valley fog likely. Some areas may see light snowfall from low-level clouds, but no significant precipitation is expected. Winds are expected to be light with variable direction. High temperatures should be in the mid 20s to low 30s F with lows in the low to mid 20s F.

Tomorrow: Chances for snow increase tonight, but it is looking like any accumulation will be light for our forecast zones. We may pick up 1 to 3” new snow, with rain or mixed precipitation up to around 200-500’. Skies should be mostly cloudy with winds averaging 10-20 mph out of the southeast. High temperatures are looking to be in the mid 20s to low 30s F with lows in the mid 20s F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 22 0 0 99
Summit Lake (1400′) 19 0 0 47
Alyeska Mid (1700′) 24 0 0 115
Bear Valley – Portage (132′) 26 0 0
Grouse Ck (700′) 27 0 0 79

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 15 WNW 3 13
Seattle Ridge (2400′) 18 W 2 12
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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.