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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, May 1st, 2022 - 7:00AM
Expires
Mon, May 2nd, 2022 - 7:00AM
Forecaster
Andrew Schauer
High Avalanche Danger
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

The avalanche danger is HIGH as a storm continues to unfold. Heavy precipitation and strong winds will make large storm slab avalanches 1-4′ deep very likely. With over an inch of rain on snow up to 1800′, large wet slab avalanches will also be likely. These avalanches have the potential to run into valley bottoms and over popular hiking and biking trails. Travel in and below avalanche terrain is not recommended. 

MONDAY AVALANCHE OUTLOOK: This will be our final avalanche advisory for the season. The avalanche danger will remain elevated tomorrow as another round of heavy precipitation and strong winds picks up early tomorrow morning, making large natural avalanches likely and human-triggered avalanches very likely. Travel in and below avalanche terrain will still be very dangerous tomorrow and is not recommended.

Special Announcements

End of Season Operations:  With the significant storm event we have decided to add one more forecast for today. This will be our final forecast of the season. We will post our springtime tips tomorrow morning, May 2. We will continue to publish observations as they come in, and will use our social media channels periodically to post pertinent info. Thank you to everybody for another great season, and have a fun and safe spring and summer!

Sun, May 1st, 2022
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
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
  • Storm Slabs
    Storm Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Well, we had planned on wrapping up our operations yesterday but it looks like mother nature had other things in mind. The mountains near Girdwood and Turnagain Pass have received 1-1.6″ water in the past 24 hours, with over 2″ in Portage and Placer. This has fallen entirely as rain at elevations below 1500′, mixed rain and snow up to 1800′, and is equal to  8-10″ snow at upper elevations around Girdwood, 1-1.5′ snow in Turnagain Pass, with over 2′ and counting in Portage and Placer. Easterly winds have been blowing at 25-50 mph since yesterday morning, with gusts as high as 80 mph at the Sunburst weather station. The storm is expected to continue through this morning before it backs off for a brief period this afternoon, bringing another 0.5-1″ moisture to Girdwood and Turnagain Pass, and 1-1.5″ to Portage and Placer.

All of this active weather will make big avalanches very likely. Don’t let the warm temperatures and rain in the valley fool you– the avalanche conditions are very dangerous today. Areas with the heaviest precipitation could see natural storm slab avalanches 2-3′ deep by the end of the day, with wind slab avalanches 4-6′ deep or deeper. Large avalanches failing in upper level start zones have the potential to run long distances into valley bottoms. With 1-2+” rain below 1500′, we can also expect to see wet avalanches running into valley bottoms. More on this in problem 2.

View from the Sunburst weather station at 11 p.m. last night. 04.30.2022

Avalanche Problem 2
  • Wet Slab
    Wet Slab
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Slab
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
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 has been raining up to 1500′ for over 24 hours now, and there is more on the way. This is making the snowpack fall apart, and we can expect to see wet snow avalanches today. This includes Wet Slabs, Wet Loose, and Glide Avalanches. Over the past week we have seen the destructive potential for these wet avalanches, and they are clearly nothing we want to mess around with. Large avalanches will likely run into valley bottoms, potentially threatening popular hiking and bike trails in the area. Dry wind and storm slab avalanches failing at higher elevations will likely be able to trigger bigger wet slabs as they run through lower elevations.

It is looking like we might have a break in the weather this afternoon before things pick up again tonight. The potential for big avalanches will remain even if we have a few hours of relatively quiet weather. Keep this potential for overhead hazard in mind if you are trying to get outside today, and avoid travelling on or below steep avalanche terrain.

This mile-wide crown on Bench Peak is indicative of the kind of avalanche the snowpack is capable of producing right now. 24 hours of rain on snow is not helping the situation. Photo: Alex Marienthal. 04.28.2022

Weather
Sun, May 1st, 2022

Yesterday: Stormy conditions ramped up through the day, with 0.9″ Snow Water Equivalent (SWE) in Girdwood, 1.6″ in Turnagain Pass, and 2.24″ in Portage. This fell as rain as high as 1800′. Easterly winds were sustained at 25-50 mph, with gusts of 60-80 mph. High temperatures were in the upper 20’s F near ridgetops and in the mid 40’s F in the valleys, with lows in the mid 20’s to mid 30’s F under overcast skies.

Today: The storm continues this morning, and another 0.5-1″ precipitation is expected in Girdwood and Turnagain Pass, with 1-1.5″ in Portage and Placer. Easterly winds are expected to back off slightly later in the morning, with sustained speeds around 25-30 mph and gusts of 40-50 mph. Overcast skies may break up for a bit this afternoon. High temperatures will be in the low 30’s to low 40’s F, with overnight lows in the upper 20’s to mid 30’s F.

Tomorrow: Active weather returns tomorrow after a short break this afternoon. We are expecting another 0.5-1″ precipitation in Girdwood and Turnagain Pass, with 1.5-2″ near Portage and Placer. The rain line will hover between 1300′ and 1600′. Daytime high temperatures should be in the low 30’s to 40F, with overnight lows in the upper 20’s to mid 30’s F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 35 10 1.6 108
Summit Lake (1400′) 36 0 0.1 27
Alyeska Mid (1700′) 34 2 0.7 N/A

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24 ENE 33 80
Seattle Ridge (2400′) 28 SE 16 69
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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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