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Sat, April 22nd, 2023 - 7:00AM
Sun, April 23rd, 2023 - 7:00AM
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. Cooler temperatures and cloud cover should make wet avalanches less likely than yesterday, but they are still possible in the afternoon especially at lower elevations and on steep south and west facing terrain. The snowpack remains dry and cold above treeline on north facing slopes, and the potential for triggering a deeply buried persistent weak layer still exists. Triggering an avalanche on a persistent weak layer 3-6′ deep is unlikely but the consequences are high, so we recommend conservative terrain selection if you are seeking out high and dry snow conditions.

PORTAGE VALLEY hikers/bikers/xc skiers: Be aware of avalanches occurring overhead as the day heats up. This area can see large wet slides that can run close to commonly traveled areas.

Sat, April 22nd, 2023
Above 2,500'
2 - Moderate
Avalanche risk
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

The gradual onset of spring wet avalanches continued yesterday with some larger wet loose and a few wet slab avalanches observed in Girdwood, Turnagain Pass, and Portage Area. With temperatures climbing into the 50s F at sea level and sunny skies there was a lot of melt going on in the snowpack yesterday.

Wet slab avalanche that released on the SW face of Pete’s S (ob here). Photo 4.21.23 from Michael Kerst

Another wet slab from a SW aspect near Explorer Peak in the Skookum Glacier area. Photo 4.21.23 from Matt Mckee

Wet avalanche debris along Penguin Ridge near Girdwood that looks like it started as a wet loose/point release and entrained lots of wet snow on the way down. Photo 4.21.23

Avalanche Problem 1
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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

Just as things were starting to get interesting, with wet slab avalanches observed yesterday on Pete’s S and in the Skookum Glacier area, the weather is reverting back to colder temperatures and cloudy skies. Highs are expected to stay in the low 30s F in the alpine today and mid to high 30s F at lower elevations. This should make wet avalanches much less likely today, but depending on how much sun finds it’s way through the cloud cover we could still see melting crusts in the afternoon and potential for wet loose avalanches especially at lower elevations and on steep southern aspects. Keep an eye out for roller balls, natural wet loose avalanches, and wet surface snow conditions as indicators of wet avalanche conditions.

Our main concern for human triggered avalanches continues to be the low likelihood but potentially high consequence scenario of finding a deeply buried persistent weak layer on shaded northern aspects which continue to hold dry snow. Earlier this week a group of skiers in Virgin Creek in Girdwood triggered a large avalanche ranging from 2-6′ deep on a steep NW aspect (see ob here). This was very unexpected since the last avalanche triggered on our deeply buried weak layer from mid-March was about three weeks ago and we have had little significant weather recently.

While we continue to believe that triggering an avalanche like this is unlikely, the possibility increases the potential consequences of seeking out steep high elevation north facing terrain. In a typical year this would be the time where conditions are prime for tackling larger objectives, but we have seen multiple close calls this week with skiers triggering avalanches and being carried over cliffs through complex terrain. The take home message is that our snowpack has some atypical weak layers this spring that make venturing into big terrain higher risk than most years. 

Other hazards associated with the spring melt cycle include cornice fall and glide avalanche release, which are both very unpredictable and can produce large avalanches. We recommend minimizing time spent underneath large cornices or glide cracks.

High elevation northerly aspects still holding onto dry snow but also potentially holding onto deeply buried persistent weak layers. Photo 4.21.23

Supportable 1-2″ thick melt freeze crust on a west aspect at about 2000′ which could still potentially melt enough to cause wet loose avalanches with the warm temperatures and cloud cover today. Photo 4.21.23

Sat, April 22nd, 2023

Yesterday: Clear sky and really warm temperatures reaching into the 50s F at sea level and mid 30s F at upper elevations. Light winds averaging 10 mph and gusting to 20 mph at upper elevations helped to cool the snow surface in some areas.

Today: Cloud cover is expected to move into the area today, starting with high elevation clouds and then progressing toward lower elevation cloud layers in the afternoon. Winds should remain light in the 5-10 mph range out of the W this morning and switch to NW this afternoon. Temperatures are expected to cool down some today, but still reach into the mid to upper 30s F at low elevations and low 30s at upper elevations. Light rain or snowfall starts later this evening but little to no accumulation is expected.

Tomorrow: Light snow showers are possible on Sunday morning with mostly cloudy skies throughout the day. Temperatures will continue to decrease as arctic air moves over the region which should keep the snow line within a few hundred feet of sea level. Winds will shift to the east Sunday afternoon and increase slightly to 10-15 mph.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 41 0 0 84
Summit Lake (1400′) 36 0 0 41
Alyeska Mid (1700′) 40 0 0 78
Bear Valley – Portage (132′) 37 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 33 W 5 19
Seattle Ridge (2400′) 39 SW 2 8
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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.