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Issued
Fri, March 29th, 2024 - 7:00AM
Expires
Sat, March 30th, 2024 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2500′. Fresh wind slabs up to 12″ deep will be forming today as a storm system impacts the forecast area with 2-8″ of new snow and 20-40 mph east winds. These wind slab avalanches are likely to cause small natural or human triggered avalanches.

Below 2500′ the avalanche danger is MODERATE. We expect that a melt freeze crust has formed on the surface at these elevations, which will limit the potential for wind slab formation to just the new snow that falls today. Wet loose avalanches will become possible as the rain line creeps up to roughly 200′ by this evening.

Special Announcements

Avalanche Forecast Survey: Simon Fraser University is collaborating with US avalanche centers to better understand how useful avalanche forecast information is for trip planning. This research will help drive development of future avalanche forecast products. Click here if you are interested in participating in a 20 minute survey.

Fri, March 29th, 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
Sat, March 30th, 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
Sat, March 30th, 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.
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

A storm system is entering the area today and bringing strong winds and snowfall. For today the winds will likely be the bigger driver of avalanche conditions, because we are only expecting 2-3″ of new snow in Turnagain Pass, 4-6″ in Girdwood, and closer to 6-8″ in Portage and Placer. The winds are expected to reach averages of 20-40 mph out of the east with gusts possible up to 60 mph.

After the past week of warm and wet weather the snowpack at lower elevations is capped by a layer of wet snow up to about 2000′. Clear skies last night as the sun was setting should have allowed that wet snow on the surface to freeze into a solid melt freeze crust, which means there won’t be much snow for the wind to transport into fresh wind slabs at lower elevations except for whatever new snow falls today. Above roughly 2000′ the snowpack remains mostly dry, with sun crusts likely on southern aspects and dry surface conditions on northern aspects. At these higher elevations fresh wind slabs will be forming today, making natural and human triggered wind slab avalanches up to 12″ deep likely. If you brave the low visibility and get up to higher elevations keep an eye out for active wind loading, shooting cracks, and small avalanches on test slopes to get a sense for where wind slabs are forming.

Storm slab avalanches could be possible within the new snow by the end of the day if the storm over performs and brings 8+” of new snow to favored locations, such as Portage or Placer Valley.

Snowfall graphic for Friday at 4am through Saturday at 4am. Courtesy of NWS Anchorage 3.29.34

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

The combination of cooler temperatures last night and clear skies around sunset should have allowed the wet snow on the surface to freeze into a solid melt freeze crust. Today we are expecting cloudy conditions and cooler temperatures, which should keep the wet snow avalanche problems isolated to the lowest elevations where rain is likely to start falling up to roughly 200′ this afternoon. For now we can pump the brakes on the transition to a spring wet snow cycle, but it will be sure to resume once temperatures rise again and the sun makes another appearance.

Prime conditions for forming a melt freeze crust on the surface, with clear skies and cooler temperatures last night ahead of the incoming storm system. Photo 3.28.24

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

We continue to find buried weak layers 1-3′ deep in the snowpack, which were responsible for a bunch of human triggered avalanches 2 weeks ago. Now that those layers have had some time to gain strength it is unlikely for a person to trigger an avalanche on them. However, it is still unsettling to have widespread persistent weak layers in our snowpack because they can be unpredictable and are capable of surprising us, so we will continue to monitor and test them moving forward.

Weather
Fri, March 29th, 2024

Yesterday: Mostly cloudy in the morning then transitioning to mostly sunny in the afternoon. No new snowfall with winds averaging 0-5 mph from the W for most of the day before switching to E around 10 pm and increasing to averages of 10-15 mph overnight with gusts up to 30 mph. Temperatures were in the high teens to mid 20s F at upper elevations and mid 20s to mid 30s F at lower elevations.

Today: Strong winds started to pick up overnight and will continue to intensify today reaching averages of 20-40 mph out of the east with gusts possible up to 60 mph. Snowfall will accompany the windy conditions starting this morning with 2-3″ expected in Turnagain Pass, 4-6″ in Girdwood, and closer to 6-8″ in Portage and Placer. Snow line will start out at sea level and rise to about 200′ during the day today. Temperatures should stay somewhat cooler today, in the low 30s F at low elevations and mid 20s F at upper elevations.

Tomorrow: Continued wind and snowfall are expected tomorrow, with an additional 6-8″ of new snow in Turnagain Pass, 8-12″ in Girdwood and Portage/Placer area. Winds will remain strong with averages of 40-55 mph out of the east at upper elevations and gusts up to 75 mph possible. Rain line is expected to creep up to 800-900′ tomorrow afternoon.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30 0 0 94
Summit Lake (1400′) 30 0 0 41
Alyeska Mid (1700′) 32 0 0 98
Bear Valley – Portage (132′) 36 0 0
Grouse Ck (700′) 34 0 0 62

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 ENE 4 28
Seattle Ridge (2400′) 27 SE 4 16
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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.