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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, April 10th, 2024 - 7:00AM
Expires
Thu, April 11th, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Avalanche danger today is directly related to how much snow fell during yesterday’s storm. A CONSIDERABLE avalanche danger exists where over a foot of new snow fell (Girdwood and Portage Valleys). Areas that saw less than a foot of new snow have a MODERATE danger (Turnagain Pass). Expect a variety of new snow avalanche issues including triggering storm slabs in the Girdwood area, wind slabs on wind loaded slope in all areas, and loose snow avalanches in steep terrain. A cautious mindset and paying close attention to how much snow snow has fallen in the area you are traveling will be key.

Daytime Warming:  Natural wet loose avalanches within the new snow are expected later today and this evening due to daytime warming and sunshine. These could be easy to trigger and entrain a lot of snow in big steep terrain.

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.

Wed, April 10th, 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 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
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
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

Natural avalanches were likely occurring yesterday during the heavy snowfall and strong winds. Areas with the higher snowfall totals likely saw the most natural avalanche activity. Hopefully we’ll get a look around today for an idea of what the storm produced. If you get out, let us know what you see!

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

A cold winter-like storm moved through yesterday, peaked in the evening, and is headed out this morning. A few lingering snow showers could be seen today, but generally skies should be clearing up by the afternoon before another storm moves in tomorrow. Snow fell mostly to sea level and totals were impressive in the Girdwood Valley where the storm overproduced.

Snowfall Totals from the past 24-hours:

  • Girdwood Valley:  18″ at Alyeska Mid Mountain (close to 2 feet in the higher terrain)
  • Portage Valley:  10-12+” estimated for mid elevations
  • Turnagain Pass:  6-10″ (possibly more on the north end of the Pass)
  • Summit Lake:  2-3″
  • Seward/Lost Lake:  6-8″ estimated from Grouse Creek Snotel

Avalanche issues will be related to the new snow and any daytime warming/sunshine this afternoon. In areas that saw over a foot of new snow expected dangerous avalanche conditions. In areas with less than a foot expect more predictable and smaller avalanches. As always, keep a close eye out for recent avalanches and any signs of instability.

Storm Slabs:  In the Girdwood and Portage areas triggering a slab avalanche 1-2 feet deep, composed of the storm snow, should be easy to do. The snow fell on either crusts on E, S, W aspects or soft old snow and surface hoar on shaded slopes. The storm just ended so today is when new slabs are the most sensitive. Sticking to the lower angles and giving these steeper slopes some time to adjust is a great way to avoid this issue.

Wind Slabs:  Varying degrees of wind slabs are expected due to the strong east winds from yesterday. Even at Turnagain Pass where less snow fell, finding wind slabs up to a foot deep that are easy to trigger would not be a surprise. Be sure to look for areas winds have drifted snow, cracking in the snow under you, and generally stiffer snow over softer snow. Wind slabs could be extra touchy if they are not bonded yet to the crust underneath or the loose dry snow on shaded slopes.

Dry snow sluffs:  Dry snow sluffs should be expected on all aspects. These could turn into moist/wet snow sluffs on solar aspects later in the day.

 

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

DAYTIME WARMING – afternoon/evening wet loose avalanches:  If the sun comes out today expect much of the new snow to moisten then avalanche quickly. Looking for rollerballs off steep slopes with rocks/vegetation is typically the first sign the snow is becoming sticky and moist. This is a precursor to the wet loose avalanche activity. New snow is extremely susceptible to the first time it warms up. Wet loose avalanches today could run far and entrain a lot of debris due to a crust underneath. Wet loose slides are also good at triggering slab avalanches in new snow on their way down.

Weather
Wed, April 10th, 2024

Yesterday:  A cold stormy day was over the region with snow falling mostly to sea level. Snowfall totals ranged from 1-2 feet in Girdwood Valley, 6-10″ at Turnagain pass, and only a few inches in Summit Lake. Ridgetop winds were strong from the east, averaging 20-30 mph with gusts in the 50-70mph range. Temperature were in the mid 30s F at sea level and teens along the high ridgelines.

Today:  Clearing skies and valley fog is expected today as the storm heads out. No precipitation is expected and ridgetop winds have died down and should blow 5-10mph from the east. Daytime warming looks to bring temperatures to 40F at sea level and 20s F in the Alpine.

Tomorrow:  Another storm is headed in for Thursday and Friday. This one also looks cold with snow close to sea level (0-500′). Snowfall estimates are 4-10″ by Friday evening with this event at this point. Ridgetop winds will bump up from the southeast into the 20-30mph range.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26 8 0.6 104
Summit Lake (1400′) 28 2 0.1 46
Alyeska Mid (1700′) 28 18 1.5 127
Bear Valley – Portage (132′) 33 4 0.8
Grouse Ck (700′) 28 6 0.6 79

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22 ENE 16 76
Seattle Ridge (2400′) 21 SE 11 43
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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.