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

A MODERATE avalanche danger remains today. On shaded slopes at the mid and upper elevations there is the potential for a person to trigger a 1 to 2 foot slab avalanche failing on a weak layer. This issue is also on solar aspects and most concerning on these aspects in the afternoons when the surface crusts become soft. Daytime warming this afternoon and evening could melt surface crusts enough for wet loose avalanches at lower elevations and on solar aspects (E, S, and W).

MONDAY – AVALANCHE OUTLOOK:  There will be no avalanche forecast tomorrow. The next forecast will be 7am on Tuesday. Monday’s avalanche danger will be similar to today. However, temperatures should be around 5 degrees higher tomorrow, making wet loose avalanches more likely during the heat of the day.

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.

Sun, April 14th, 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
Mon, April 15th, 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
Mon, April 15th, 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
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 several wet loose avalanches that were reported during yesterday afternoon’s warm weather. These were both natural and human triggered. All these were reported to be on the smaller side. Evidence of a handful of storm slabs from the stormy weather late last week were seen in the Portage/Whittier region. These were naturally occurring from the storm – more details HERE. There was also a recent glide avalanche seen in the Skookum drainage.

 

A bunch of skier triggered rollerballs, the precursor to wet loose avalanches, on a southerly slope in the Portage/Whittier region. Photo by Graham Predeger 4.13.2024.

 

Recent glide avalanche in the Skookum drainage. Seen from the Seward Highway. Aleph Johnston-Bloom, 4.13,2024.

 

Avalanche Problem 1
  • 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

Mostly sunny skies and springtime weather is expected again today and into tomorrow, Monday. With many folks seeking out cold dry powder on mid and upper elevation shaded slopes, be aware there is a lurking weak layer. This layer is a combination of small facets and buried surface hoar. It has also been found on solar aspects on top of a crust. On these solar aspects, triggering a slab is much more likely when the surface crusts are soft and melting.

A skier remotely triggered a slab in the Girdwood area on Friday that was around 2 feet deep (more details in John’s forecast from yesterday) and a group at Turnagain Pass had multiple unstable test results on an upper elevation northerly aspect yesterday. Hence, triggering what appears like a surprise slab avalanche is within the realm of possibilities. The video below is from that group and shows one of two Extended Column Tests they performed. They were in the upper Spokane Creek area on a north aspect at 3,400′. How reactive this layer is in the forecast zone is uncertain, which is common for these tricky weak layers. Having a crust underneath makes them tricker. Crusts can prolong the healing process and provide a slick bed surface if an avalanche was to be triggered.

We recommend carefully evaluating how well the snow from last week is bonding to the old snow/crust underneath before committing to steeper terrain. Persistent weak layers can cause avalanches on lower angle slopes and be triggered remotely (from the side, top, or bottom). To avoid the problem entirely you can always stick to lower angle terrain.

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

With a clear night, we can expect a solid re-freeze in the lower elevations and on most solar aspects. With cool ambient temperatures today it may take the sun until later this afternoon to soften the crusts. As is a normal springtime routine, keep a close eye out for when the crusts do soften. Once the top several inches are wet and saturated, then wet loose avalanches should become easy to trigger.

Cornices:  Strong sun can also cause cornices to start breaking off, and there are a lot of ridgelines still holding onto huge cornices. Try to avoid spending time underneath cornices if they are receiving direct sunlight and give them a wide berth if you are traveling along a corniced ridge.

Glide Avalanches:  As the spring rolls on, don’t forget to watch for dark opening cracks on slopes. These are glide cracks and can release into a very destructive avalanche at anytime. If needing to pass under them, we recommend go fast and one at a time. If possible, avoiding being under them is the safest choice.

Weather
Sun, April 14th, 2024

Yesterday:  Mostly sunny skies with some patchy clouds were over the region. Ridgetop winds were moderate from the east until around noon when they turned northwesterly and were light. Temperatures reached near 30F along ridges during the afternoon warmup and in the mid 40s F at sea level.

Today:  Another mostly sunny springtime day is expected. Ridgetop winds are northwesterly and should average 5-10mph with gusts in the teens. Temperatures are chilly this morning (teens to 20s F) but should rise again to near 30F at the mid elevations and 40s F at sea level.

Tomorrow:  Monday looks to be another mostly clear sky day, yet ridgetop winds turn southerly bringing in warmer air (5-10mph). Hence Monday’s temperatures should be a notch higher, 30F near the higher peaks and close to 50F at sea level. Beginning Tuesday and through the end of the week, more active weather could be returning depending on where the low pressure in the Gulf sets up. This would bring some rain and wind. Stay tuned on Tuesday’s forecast.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 0 0 99
Summit Lake (1400′) 28 0 0 46
Alyeska Mid (1700′) 29 0 0 116
Bear Valley – Portage (132′) 33 0 0
Grouse Ck (700′) 31 0 0 74

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 NNW 8 32
Seattle Ridge (2400′) 25 NNW 2 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.