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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, April 20th, 2024 - 7:00AM
Expires
Sun, April 21st, 2024 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. With little or no refreeze for the past two nights and warm temperatures with partly to mostly sunny skies on the way, we are expecting to see wet loose avalanches as the snow surface heats up. Be on the lookout for natural avalanches on steep southerly slopes later in the day. Additionally, the easterly winds that have been blowing since Wednesday are expected to continue this morning before dying down this afternoon, and we may still be able to trigger a wind slab avalanche on slopes that have been recently loaded.

Special Announcements

Avalanche Center End of Season Operations: We are continuing to issue forecasts 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.

Sat, April 20th, 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
Sun, April 21st, 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
Sun, April 21st, 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 no new avalanches reported yesterday. We have continued to see glide cracks opening along the Seward Highway from Bird Point down to Seward, including some new activity on Seattle Ridge.

New glide crack opening on the front side of Seattle Ridge, just above the parking lot. 04.19.2024

Avalanche Problem 1
  • 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

It’s been a slow transition, but it is looking like we’re headed into spring. We’re expecting another day of mild temperatures with partly to mostly sunny skies, and the easterly winds that have been howling through the area for the past two days should hopefully die down this afternoon.

The most likely avalanche to encounter today will be a wet loose avalanche. These will start happening on steep southerly slopes near rocks or trees where the snowpack heats up the quickest. We may also see avalanches happening on east- and west-facing slopes as temperatures rise through the day. After over two days with above-freezing temperatures it shouldn’t take a whole lot of daytime warming to make avalanches happen. Be on the lookout for rollerballs rolling down the slope as an indicator of deteriorating conditions, and head to shaded aspects if you start noticing wet and sloppy snow on the surface.

Glide Avalanches: We are continuing to see new glide cracks opening up, with a few small glide avalanches releasing over the past two weeks. These avalanches are impossible to predict, so it’s important to avoid spending any time below open glide cracks.

This week’s wind storm has covered a lot of terrain with dust. These darker surfaces will heat up quicker than snow normally would, and may increase the likelihood of wet snow avalanches. 04.19.2024

Avalanche Problem 2
  • 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

The wind has been at work since Wednesday night moving snow around. Thankfully it should start dying down today, but there is still a chance that we’ll be able to find reactive wind slabs out there. It has been two days since the worst of the winds passed, so the main avalanches we’ll be on the lookout for will be smaller slabs that have formed over the past 24 hours. With such strong winds over the past two days, there is probably very little soft snow left to be blown into reactive slabs. However, the wind always seems to find some snow to blow around.

Watch for dangerous conditions in the usual places- below ridgelines, convex rolls, and in steep gullies. Given how strong the winds have been, we may find sensitive slabs further downslope than what we would ususally expect to see. We will also probably see stiffer wind slabs which may allow a person to get well out onto a slope before triggering an avalanche.

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 layers in the upper 2-3′ of the snowpack that were making avalanches over a week ago seem to be unreactive at this point. That said, with a major wind loading event combined with sustained warm temperatures, it’s still something we are paying attention to. Although we don’t expect to see people triggering avalanches deeper in the snowpack there may be some isolated slopes where one of these layers could produce an avalanche. The most recent observation showing cause for concern came last Saturday from a group in Spokane Creek that changed their plans after digging a pit and finding unstable test results. If you are considering getting into more consequential terrain, it is a good idea to take a minute to dig down and assess the upper 3′ of the snowpack.

 

Weather
Sat, April 20th, 2024

Yesterday: Strong easterly winds continued to blow through the area, with average speeds of 20 to 45 mph and gusts of 50 to 75 mph. Clouds slowly broke up through the day, with overcast skies in the morning and partly sunny skies later in the afternoon. Temperatures reached the mid 30s to low 50s F, with lows in the low 30s to mid 40s F. No precipitation was recorded.

Today: These east winds are finally looking to start backing off, with sustained speeds tapering from around 30 mph to 10 mph by this afternoon. We are expecting to see high clouds lingering through the day, with partly sunny skies. High temperatures are expected to be in the upper 30s to low 50s F, with lows in the upper 20s to low 30s F. No precipitation is expected today.

Tomorrow: A low pressure system is slowly moving into the area tomorrow, with increasing clouds and a chance for precipitation later in the day. We will most likely only see a trace of precipitation by tomorrow night, with maybe 2” snow at upper elevations closer to the coast. Rain line is looking to be around 1600-1800’. Winds should be out of the east at 5 to 15 mph with gusts of 10 to 25 mph. High temperatures are expected to be in the mid 30s to low 40s F, with lows in the upper 20s to mid 30s F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 44 0 0 92
Summit Lake (1400′) 44 0 0 41
Alyeska Mid (1700′) 44 0 0 106
Bear Valley – Portage (132′) 51 0 0
Grouse Ck (700′) 43 0 0 68

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 32 ENE 38 72
Seattle Ridge (2400′) 37 SE 13 33
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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.