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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, March 16th, 2024 - 7:00AM
Expires
Sun, March 17th, 2024 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger remains CONSIDERABLE above 1000′. The potential to trigger a large avalanche on a buried weak layer 2-5′ deep still exists. Smaller avalanches in wind loaded areas about 1′ deep are likely today, as snowfall and strong winds impact the forecast area. We recommend sticking to low angle terrain and avoiding runout zones of overhead avalanche paths to avoid the potential to trigger a large avalanche. Below 1000′ the avalanche danger is MODERATE. Rain is expected to fall up to 1100′ by this afternoon, which will make wet loose avalanches likely on steep low elevation terrain features.

ROOF AVALANCHES: As the snow turns to rain roof avalanches will become a hazard again. Be aware of where you park your car, enter buildings, and where your kids and dogs are playing relative to snow laden roof lines.

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.

Sat, March 16th, 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
Sun, March 17th, 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
Sun, March 17th, 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

No new avalanche activity was reported yesterday.

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 fresh round of wind and snow are moving in today, with 3-6″ of new snow expected and rain line moving up to 1100′ throughout the day. Wind speeds should pick up as the storm intensifies around 10 am, with averages of 20-30 mph out of the east and gusts up to 50 mph. The new snow is not expected to be deep enough to cause avalanches in sheltered locations. Areas with active wind loading where the new snow and soft snow already on the surface is being blown into fresh wind slabs will be the most likely place to trigger an avalanche roughly 1′ deep. To identify these areas you can look for active wind transport on the snow surface, feel for hollow wind slabs sitting on top of softer surfaces, and check small test slopes for shooting cracks or small avalanches.

Loose snow avalanches are also likely today. Dry loose avalanches or sluffs can be found in steep terrain that has soft snow on the surface. Wet loose avalanches are likely at low elevations where rain could cause small avalanches to release naturally on steep terrain features.

Snowfall totals from 4am Saturday to 4am Sunday. Graphic courtesy of NWS Anchorage 3.16.24

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.
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 potential to trigger a larger avalanche on a buried weak layer 2-5′ deep is the greater concern today. On Thursday there were at least 8 human triggered avalanches reported, most of which appear to have failed on some kind of buried weak layer. Luckily nobody was caught or buried in any of these incidents, but most of the human triggered avalanches reported were large enough to bury a person. We believe the weak layers causing these avalanches are either buried surface hoar or facets associated with sun crusts which were buried last weekend at the onset of the snow storm that brought 2-5′ of new snow to the forecast area over 4 days.

Several of the avalanches reported on Thursday appeared to be remotely triggered, which means you can cause an avalanche from low angle terrain above, below, or to the sides of steeper terrain. Buried persistent weak layers are difficult to assess in the field and even digging snowpits to test the weak layers can provide false stable or inconsistent results. The best way to manage this type of avalanche problem is to take a conservative approach to selecting terrain by sticking to lower angle slopes and avoiding the runout zones of overhead avalanche paths. The snowpack needs some time to heal these buried weak layers.

Large skier triggered avalanche on Sunburst from Thursday, the 10th skier on slope triggered the avalanche and took out the old tracks. Photo from Billy Finley 3.14.24

Weather
Sat, March 16th, 2024

Yesterday: Cloudy skies and mostly light winds averaging 0-10 mph with gusts up to 20 mph out of the east. Temperatures stayed in the teens to low 20s F at upper elevations and low 20s to low 30s F at lower elevations. No new snowfall was recorded.

Today: Another round of snowfall is starting this morning, with about 0.25-0.5″ of water or 3-6″ of snowfall expected during the day on Saturday. Coastal areas near Portage and Whittier could see twice that much precipitation, with 6-12″ during the day today. At the start of the storm snow should fall down to near sea level with rain line gradually creeping up to about 1100′ by this afternoon. Temperatures are expected to reach highs in the low to mid 30s F at mid elevations today and high 20s F at upper elevations. Winds are expected to increase as the snowfall begins around 8am this morning, with averages of 25-30 mph and gusts up to 50 mph out of the east.

Tomorrow: Sunday looks similar to today, with continued snowfall and moderate SE winds averaging 20 to 30 mph with stronger gusts. Rain line is expected to move up to 1600′ on Sunday with temperatures reaching in the mid 30s F at mid elevations and low 30s F at upper elevations.  Another 0.25-0.5″ of water or 3-6″ of snowfall is expected on Sunday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 25 0 0 107
Summit Lake (1400′) 24 0 0 47
Alyeska Mid (1700′) 27 0 0 106
Bear Valley – Portage (132′) 27 1 0.1 –
Grouse Ck (700′) 27 0 0.0 73

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 NE 6 20
Seattle Ridge (2400′) 22 E 3 9
Observations
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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.
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