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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, April 16th, 2022 - 7:00AM
Expires
Sun, April 17th, 2022 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 2500′. Lingering wind slabs created over the past 24 hours could be up to a foot deep and are possible for a person to trigger. These should be isolated to upper elevation ridgelines, cross loaded gullies, and convex rollovers. If the clouds break up and the sun comes out today wet loose avalanches and cornice fall will become likely on southern aspects. Glide avalanches are also a real concern today, as we have seen a lot of glide releases in the past week on southern aspects and there are a lot more glide cracks still visible in areas that get a lot of traffic.

Below 2500′ the avalanche danger is LOW. We did not observe any active wind loading at these lower elevations yesterday, but it is worth keeping an eye out for lingering wind slabs toward the upper end of the treeline elevation band. A mix of supportable crust, breakable crust, and dry snow exists on different aspects.

Special Announcements
  • End of Season Operations:  This will be the final week of 7 day/wk forecasts. Beginning Monday, April 18, we will only be issuing forecasts on Tuesday, Thursday, Saturday and Sunday. The final forecast will be on Saturday April 30th.
Sat, April 16th, 2022
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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.
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • 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.
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

Our area remains stuck between a low pressure system in the Bering Sea and a high pressure system in interior Alaska and Canada, which has caused increased wind speeds and cloud cover over the past 24 hours along with occasional light snowfall or rain. Winds and cloud cover are expected to decrease throughout the day and no significant precipitation is expected today. Lingering wind slabs created over the past 24 hours are the primary avalanche problem and could be up to a foot deep and possible for a human to trigger. To identify areas with recent wind loading look for signs of wind transport on the snow surface, hollow feeling snow, and shooting cracks along ridgelines, cross loaded gullies and convex rollovers. These wind slabs should be isolated to upper elevation areas that had stronger winds yesterday (see obs here and here).

If the cloud cover decides to really back off and the sun makes an appearance today then we could see wet loose avalanches on solar aspects, cornice fall from solar warming, and more active glide avalanche activity (see problem 2). Over the past week cool temperatures have been holding spring at bay and minimizing the amount of melt on solar aspects. However, a large wet loose avalanche on Penguin Ridge on Thursday is a good reminder that in steep terrain with enough melted snow at the surface you can easily trigger a wet avalanche large enough to bury a person. Be aware of how much melt is happening on southern aspects today if the sun comes out and avoid travelling on slopes that are more than ankle deep with melted snow.

Mostly cloudy conditions yesterday kept the sun from melting much, but if the clouds clear today wet loose avalanches and cornice fall could be an issue again. Photo 4.15.22

Avalanche Problem 2
  • Glide Avalanches
    Glide Avalanches
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
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

Glide avalanche activity has been widespread on southern aspects in Turnagain Pass and throughout the forecast area this week. Plenty of glide cracks remain that have not released yet and we should be extra careful to avoid spending time underneath glide cracks during this period of higher likelihood for them to release. Some of the most notable glide cracks still waiting to release are on Repeat Offender just south of the motorized up track. The avalanches created by glide crack releases are typically very large and destructive because they involve the entire depth of the snowpack and often have wet snow in the debris. This is one type of avalanche you do not want to mess around with!

Lots of glide cracks poised to release on the northern end of Seattle Ridge as the spring melt continues. Photo 4.15.22

Weather
Sat, April 16th, 2022

Yesterday: Overcast to mostly cloudy with occasional snow flurries during the day. Winds were light in the treeline elevation band and moderate at upper elevations with averages in the 5-15 mph range and gusts up to 35 mph along ridgelines.

Today: Similar to yesterday, but with decreasing winds speeds and cloud cover throughout the day. Temperatures should be in the 30’s at lower elevations and 20’s at upper elevations. Snow flurries are possible and most likely along coastal areas.

Tomorrow: Over the weekend and into early next week we are positioned at the boundary between a low pressure system in the Bering Sea and a high pressure system over the Alaska and Canadian interior. Occasional flurries and variable cloud cover are likely, but no significant precipitation is expected. Temperatures should remain relatively steady and wind speeds should stay light into early next week.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 0 0.1 108
Summit Lake (1400′) 32 0 0.3* 37
Alyeska Mid (1700′) 34 0 0 NA

*Forecaster Note: Low confidence that this much precipitation happened in the last 24 hours in Summit Lake, this is likely an anomaly of the weather stations sensors.

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 E 12 35
Seattle Ridge (2400′) 24 SE 11 19
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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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