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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, March 31st, 2024 - 7:00AM
Expires
Mon, April 1st, 2024 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′. Some parts of our advisory area received 1.5 to 2 feet of snow in the past 24 hours, with winds reaching over 100 mph. The weather is expected to be a bit calmer today, but dangerous avalanche conditions will remain. It is likely a person will be able to trigger a wind slab avalanche around 1 to 3 feet deep or deeper. For the areas near Girdwood and Placer that received the most snow yesterday, it may still be possible to trigger a big avalanche on sheltered slopes as well. Pay close attention to how the new snow is behaving today, and be cautious of steep terrain where fresh wind slabs have formed or where there is enough new snow to make bigger avalanches. Elevations below 1000′ have seen continued rain on snow and warm temperatures, making for MODERATE danger below treeline with wet loose avalanches the main concern.

 

Special Announcements

The National Weather Service has issued a Winter Weather Advisory through 10:00 this morning for the active weather we are currently seeing.

Motorized Area Closure for Skookum Valley:  Per the National Forest Plan the Skookum Valley is closed to motorized use beginning April 1. Placer Valley remains open along with all other areas on the Forest.

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.

Sun, March 31st, 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
Mon, April 1st, 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
Mon, April 1st, 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

We didn’t get any reports of fresh avalanche activity yesterday. However, with limited visibility and low traffic in the mountains, there is a good chance that some natural activity went unnoticed.

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 major storm event is wrapping up this morning, but avalanche conditions are expected to remain dangerous today. The snow totals have varied widely across the advisory area, but the wind was a constant throughout our zone. Stations recorded gusts over 100 mph yesterday evening, with several hours of speeds averaging 50 to 80 mph for 5 hours. That has done some serious work moving snow, and will make wind slab avalanches the main concern today. In addition to those wind slabs, we should also be traveling cautiously in the areas that picked up the most snow yesterday. Here’s what we have for storm totals for the past 48 hours:

Girdwood: 2-3 feet snow equaling 2.3-2.8″ Snow Water Equivalent (SWE)

Portage/Placer: 1.5-2 feet snow equalling 1.9″ SWE

Turnagain Pass: 6″ snow equaling 0.8″ SWE

It can be a challenge to predict how the snow is going to behave after a wind event like we saw last night. There are a few things that we should be paying close attention to today. First, we often see wind slabs form much lower on slopes when the winds are unusually strong. This can catch us by surprise because we might see relatively stable conditions at the top of the slope before triggering an avalanche mid-slope. We also see very stiff wind slabs forming with these strong winds. That can allow a person to get way out into the middle of a slope before triggering an avalanche, making it difficult or impossible to get off a moving slab. It can also allow several sets of tracks on a slope before someone triggers an avalanche.

Conditions are likely to be tricky today, and there is potential to trigger big avalanches. Travel cautiously, and avoid steep terrain if you suspect there may be a fresh wind slab on the surface, or if you are traveling in one of the areas that received the heaviest snowfall in the past 48 hours.

Turnagain Pass didn’t get nearly as much snow as Girdwood yesterday, but certainly got the wind. Photo from Tincan yesterday afternoon, 03.30.2024

Predicted snow totals for the next 24 hours. Most of this is expected to arrive this evening. Graphic courtesy of NWS Anchorage, 03.31.2024

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

Elevations below around 500 feet have seen heavy rain for the past two days, and haven’t gotten a solid refreeze in about a week. The snow is wet and sloppy, and there is a good chance a  person will be able to trigger a wet snow avalanche below treeline. These can be small and easy to manage, but they can also pick up a lot of volume as they chug along and can be incredibly destructive. Be on the lookout for wet snow avalanches at the lower elevations. They may not seem as dangerous as bigger dry slab avalanches, but they can have severe consequences if you are caught and carried.

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

The weak layer of snow that was buried earlier in the month is being put to the test by this loading event. We haven’t seen any activity on this layer in two weeks, and it has been showing signs of gaining strength in snow pits. However, we are still paying close attention to it, especially as it responds to the stress that was just added. For now, this is another good reason to dial back terrain choices today. Hopefully we don’t see any activity on this layer following the storm and we can stop worrying about it.

Weather
Sun, March 31st, 2024

Yesterday: We saw a fast-moving storm impact the area yesterday, bringing 1.5-2’ of snow equaling 1.5-2” SWE in the past 24 hours to upper elevations near Girdwood, Portage, and Placer, and only 4-6” equaling around 0.5” near Turnagain Pass and Summit Lake. Seward received around 10-12” for roughly 1” SWE. Rain line was as high as 800 feet during the day, dropping to around 500 feet overnight. Winds were exceptionally strong yesterday evening, with ridgetop speeds averaging up to 80 mph and gusts as high as 123 mph at the Sunburst weather station! High temperatures ranged from the upper 20s to upper 30s F, with lows in the low 20s to low 30s F.

Today: We should see things calm down a bit during the day before another round of active weather passes tonight. Winds are expected to taper down through the day, with speeds averaging 20-40 mph this morning, backing down to 10-20 mph by this afternoon. We may see a trace to a few inches of snow at or near sea level during the day, with the potential for some sun poking through the clouds this afternoon. High temperatures are expected to be in the mid 20s to low 30s F with lows in the upper teens to low 20s F.

Tomorrow: A fast-moving system is expected to pass through tonight into tomorrow, bringing another 2-6” snow to Girdwood, Turnagain Pass, and Summit Lake, with slightly more in Portage and Placer and up to 12-14” near Seward. Rain levels should stay down around 100 to 300’ for this next round of precipitation. Strong winds are expected to continue to average 20-30 mph overnight, quickly backing down to 5-10 mph starting tomorrow morning. High temperatures should be in the mid 20s to low 30s F, with lows in the mid to upper teens F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30 4 0.6 99
Summit Lake (1400′) 31 5 0.5 N/A
Alyeska Mid (1700′) 31 16 1.46 114
Bear Valley – Portage (132′) 37 rain 1.57
Grouse Ck (700′) 35 3 1.0 67

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21 ENE 32 123
Seattle Ridge (2400′) 25 SE 16 39
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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.