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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, April 16th, 2024 - 7:00AM
Expires
Wed, April 17th, 2024 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations today. At upper elevations winds started to pick up overnight and fresh wind slabs up to 1′ deep could be triggered by a person or release naturally today. At lower elevations above freezing temperatures could lead to wet loose avalanches on steep terrain. There is an outside chance a person could trigger a deeper avalanche 1-2′ deep on a buried weak layer at upper elevations.

WEDNESDAY – AVALANCHE OUTLOOK: Strong winds are expected to pick up late on Tuesday and continue throughout the day on Wednesday, with averages of 30-40 mph and gusts up to 65 mph out of the east. Wind slabs 1-2′ deep are likely to form and could release naturally, especially at upper elevations where plenty of dry snow exists on northern aspects. If temperatures stay above freezing and clouds prevent a crust from forming at lower elevations wet loose avalanches will be possible on steep terrain below treeline.

Special Announcements

Avalanche Center End of Season Operations: 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.

Tue, April 16th, 2024
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Wed, April 17th, 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
Wed, April 17th, 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

With good visibility yesterday we were somewhat surprised not to see more wet avalanche activity after the warm and sunny day on Sunday. There were roller balls on many steep southern aspects and a few larger wet loose avalanches on the SW face of Sunburst. The light winds during the day yesterday were definitely helping to keep the snow surface cool and may have been minimizing the effects of sun to create wet avalanche conditions. We did see one new small glide avalanche on a south aspect of Penguin Ridge above Girdwood.

Small glide avalanche that released naturally Monday afternoon. Photo 3.16.24

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

Winds started to pick up overnight, with averages of 10-15 mph and gusts up to 30 mph out of the east. These winds are expected to persist throughout the day today and then increase overnight tonight. On Wednesday winds are expected to average 30-40 mph with gusts up to 65 mph out of the east. Despite the past few days of sunny and warm weather, there is still plenty of soft snow at upper elevations on northern aspects to form fresh wind slabs. Today these wind slabs will probably be fairly small, ranging from roughly 6-12″ deep. Tomorrow, as the winds become very strong, larger wind slabs are likely to form up to 1-2′ deep in areas where soft dry snow exists on the surface.

Wind slabs tend to form along upper elevation ridgelines, gullies, and convex rollovers. Some good tests to identify wind slabs include using hand pits, jumping on small test slopes, and stepping off the beaten path to feel for hollow, drum like snow surfaces. Shooting cracks or small avalanches on test slopes are strong signs that wind slabs are sensitive to the weight of a skier or rider in your area.

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

At lower elevations temperatures stayed pretty warm last night, with lows in the mid 30s F and cloudy skies this morning. Depending on when those clouds moved into the area and how much of a re-freeze the wet snow on the surface got last night wet avalanche conditions could develop later in the day. The cloud cover should help block out the sun somewhat today, but wet loose avalanches may still be possible below treeline. Keep an eye out for wet snow on the surface, and if you are sinking in more than ankle depth it is best to avoid steep terrain where wet avalanches could start.

A few recent glide avalanches have also be observed in Turnagain Pass and Girdwood over the past few days. Glide avalanches can release spontaneously and cause very large and destructive avalanches. If you see a glide crack on the slope above you it is best to avoid spending time underneath.

Recent wet loose avalanches on the SW aspect of Sunburst that look like they were skier triggered on Sunday late in the day. Photo 3.16.24

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

It’s been four days since the last human triggered avalanche occurred on a buried weak layer of surface hoar and facets about 1-2′ deep. We saw a lot of tracks on steep terrain in Turnagain Pass yesterday with no signs of slab avalanches being triggered. This is an encouraging sign, but it doesn’t necessarily mean that we are out of the woods yet. Persistent weak layers can lie dormant for extended periods and then become active again if they are loaded with new snow or wind. The chances of triggering an avalanche on a buried weak layer seems low right now, but it would not be impossible. To evaluate whether buried weak layers are an issue where you are travelling you can always dig down a couple feet and test the snowpack using stability tests like a compression test or extended column test.

Weather
Tue, April 16th, 2024

Yesterday: Clear skies and warm temperatures, reaching 40 F up to about 2000′ but staying cooler at about 25 F at upper elevations. Winds were light during the day with averages of 5-10 mph out of the east before increasing overnight with averages of 10-15 mph and gusts up to 30 mph out of the east.

Today: Mostly cloudy skies are expected today with temperatures reaching highs in the 40s F at low elevations and mid 20s F at upper elevations. Winds should remain in the 10-20 mph range with gusts up to 25-30 mph. No new snowfall is expected today.

Tomorrow: Mostly cloudy skies are expected to remain tomorrow, with temperatures reaching highs in the 40s at low elevations and mid 20s at upper elevations. Winds are expected to increase to averages of 30-40 mph and gusts up to 65 mph out of the east. Snow showers are possible, but no significant new snow accumulation is expected until Thursday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 0 0 98
Summit Lake (1400′) 32 0 0 46
Alyeska Mid (1700′) 33 0 0 114
Bear Valley – Portage (132′) 37 0 0
Grouse Ck (700′) 36 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 ENE 10 30
Seattle Ridge (2400′) 27 SE 9 20
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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.