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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, March 14th, 2024 - 7:00AM
Expires
Fri, March 15th, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Dangerous avalanche conditions exist. Today is the first sunny day after a storm that deposited 3 to 5 feet of snow in 2 1/2 days. The avalanche danger is CONSIDERABLE at all elevations. Triggering a large slab avalanche 3 to 5 feet deep could be easy to do and result in an unmanageable situation. Warming by the sun can make slopes more unstable and easier for people to trigger these slabs. The sun is also likely to cause wet loose avalanches on southerly aspects that could trigger a slab below.

*Statistically these are the most likely days for an avalanche accident. A cautious mindset is recommended. Sticking to lower slope angles (30 degrees or less) and well away from avalanche runouts is a good way to enjoy the powder and avoid the avalanche problem.

Special Announcements

Turnagain Pass Avalanche Awareness Day – Saturday, March 23!
Swing by the Turnagain motorized parking lot between noon and 4pm to grab a hotdog, practice your beacons skills, chat with the forecast team, and possibly test out a demo snowmachine provided by local dealers. This is a fun day designed to connect with our excellent backcountry community!

Thu, March 14th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
Avalanche risk
Fri, March 15th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
Avalanche risk
Fri, March 15th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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 a handful of slab avalanches that appeared to be triggered by the sun near Girdwood yesterday afternoon. These were on southerly facing slopes. The slabs were likely barley hanging on when the sun warmed them enough to push them over the balance. Photo below of one taken from the Forest Service office.

There was also a skier triggered slab in the upper Girdwood Valley, no one caught. This was reported to be up to 2 feet deep. The Girdwood area had less snow from the storm, around 2 feet vs the 3 to 5 feet seen in Turnagain and Placer Valley.

One of several storm slabs that released yesterday. This one seen from the Forest Service office in Girdwood at 5pm. 3.13.24.

 


Skier triggered storm slab in the upper Girdwood Valley. No one caught. Thanks to Matt Yoder for the photo. 3.13.24. 

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

What a storm that just wrapped up. Over the past three days, from Monday morning through last night several feet of snow has fallen. Estimated storm totals listed below. Early this morning skies began to clear and winds turned northwesterly. Although the wind is bringing in cooler air, daytime warming today should be a factor. With the time change last Sunday, solar noon is now just after 2pm. This means the hottest part of the day for the rest of spring will be 2 to 5pm. More on the sun effect in Problem 2.

For today, the message is simple: A lot of new snow in a short time falling on questionable weak snow surfaces equals the potential for very large and dangerous human-triggered avalanches. These avalanches could be triggered remotely, meaning from the side, top, or bottom of a slope.

Storm Slabs:  There is just too much uncertainty as to how well the new snow will bond to the underlying surfaces. Below the storm snow the lower elevations have a mix of facets over slick crusts, the southerly slopes have possibly buried surface hoar on top of a sun crust, shaded slopes have a mix of facets over wind-hardened snow. It’s a mixed bag of weak snow that sits under all this storm snow and some slopes may heal and bond quickly while others do not. Regardless, snow science tells us that the first day after the storm is inherently dangerous, even if there is no weak snow underneath to deal with.

Wind slabs:  The winds were strong enough to load slopes in the higher elevations and will only make these slab avalanches larger. It will be great to see how the winds affected the snow as today will be our first look.

Cornices:  We should be extra careful along ridgelines. Cornices have likely grown and changed shape. These could be teetering on the brink of failure and if one falls off, which is dangerous in itself, could also trigger a large slab below.

Estimated storm totals from Monday morning through last night:

Turnagain Pass:  3-4 feet of snow
Girdwood Valley:  2 feet of snow
Placer Valley:  4-5 feet of snow
Summit Lake:  6-10 inches of snow

 

Over 4 feet of snow fell in this location that has settled to just over 3 feet. This is around 1,200′ in the trees just to the north of the Turnagain motorized parking lot. 3.13.24.

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

Sunshine today is likely to warm the snow surface enough to create wet loose avalanches on solar aspects. A small wet loose avalanche isn’t very exciting, but with so much new snow, it could be either quite large in bigger terrain and/or also trigger a slab below. Additionally, daytime warming can penetrate the snowpack and make the new snow that’s trying to bond to the old snow more unstable. Just another reason to play it safe today and let the steeper slopes adjust on their own.

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

Several inches to a foot below the new storm snow are various layers of even older weak snow and crust mixes. Essentially, all this new snow is overloading multiple questionable layers and if one of these fails it could propagate widely and produce a large avalanche. This is something we’ll be sussing out in the days to come.

Weather
Thu, March 14th, 2024

Yesterday:  Heavy snowfall continued yesterday in Portage/Placer/Turnagain but broken skies and light snowfall was seen in Girdwood as well as Summit Lake. New snow amounts for the past 24-hours were anywhere from 2-10″ depending on location. The storm shut off last night and skies are clearing this morning. Ridgetop winds were easterly 10-20mph with gusts near 50 during the snowfall, but have turned northwesterly early this morning and blowing 5-10mph. Temperatures were 20’s to 30 F but have cooled overnight to the teens and 20s F.

Today:  Mostly clear skies are forecast today with possibly some patchy fog. Ridgetop winds should stay northwesterly in the 5-10mph range with some gusts near 20mph. Temperatures may climb to near 40F at sea level with the daytime warming and near 30F in the mid elevations.

Tomorrow:  A weak weather disturbance pushes through Friday that could bring cloudy skies and possibly a trace of snow. Ridgetop winds turn easterly averaging 5-10 mph with gusts near 20. Temperatures should remain cool, in the teens to 20F. Looking at the weekend, models are hinting at a warm and wet storm headed our way.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24 6 0.5 113
Summit Lake (1400′) 25 2 0.1 47
Alyeska Mid (1700′) 23 3 0.2 109
Bear Valley – Portage (132′) 33 8 0.9
Grouse Ck (700′) 32 2 0.2 74

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 16 ENE 18 51
Seattle Ridge (2400′) 21 ESE 8 24
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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.