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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, February 23rd, 2022 - 7:00AM
Expires
Thu, February 24th, 2022 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE at elevations above 2,500′ on all aspects. Increasing easterly winds today ahead of another storm tonight is expected to create new wind slabs. These should be easy to trigger on any freshly wind loaded slope and in the 1′ deep realm. Wind slabs have the potential to step down and create a larger avalanche in buried weaker layers that exist in certain parts of the forecast zone. Additionally, lingering storm slab avalanches (at elevations above 1,000′) could be found in the Girdwood area where significantly more snow fell Monday night.

*The avalanche danger is expected to rise through the next two days as a series of powerful storms is headed this way. 

SUMMIT LAKE:  This region has a much thinner and weaker snowpack compared to Turnagain. Avalanches are more likely to step down into buried weak layers and create a larger and more dangerous slide.

Wed, February 23rd, 2022
Alpine
Above 2,500'
3 - Considerable
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

A large avalanche occurred Monday night on the Goat Shoulder in the Crow Creek area of Girdwood Valley. The debris filled the creek and associated powder blast struck a structure on the other side of the creek (no damage sustained). This happened during heavy snowfall and strong winds during Monday night’s storm. A few more details HERE.

Crown of the avalanche on the Goat Shoulder that occurred Monday night. Avalanche started at 2,800′ and was on a southwest aspect. Rough estimates are up 600′ wide, 5′ deep, and running 1,500′. Photo taken on Tuesday, 2.22.22.

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

After a 24-hour break in stormy weather, the easterly ridgetop winds are forecast to be on the rise today. They will be blowing 30-40mph with stronger gusts and the primary driver for avalanche concerns before the snow starts tonight. We can expect around 3-6″ tonight with 2-3′ (yes feet…) on the way tomorrow through Friday. Although the surface is somewhat wind affected from the last storm, there should still be plenty of snow available for transport into new wind slabs.

Watching for changing conditions, especially active wind drifting/loading, will be key today. This is along with the regular red flags (cracking in the snow around you and whumpfing/collapsing in the snowpack). There was a dramatic difference in new snow amounts from the last storm (Monday afternoon through Tuesday morning). Turnagain only ended up with around 6″ compared to Girdwood Valley in the 14-20+” range (Alyeska reported 22″). The Monday night storm covered a layer of small surface hoar (2-5mm), but we were unable to find it yesterday on Tincan. It was likely blown over and/or intermixed with the snow. That was only one small area, therefore it could still be present under Monday’s snow. As new wind slabs form, there is a chance they could be larger and propagate wider due to this buried layer.

Girdwood Valley:  With so much more snow from Monday night in the Girdwood Valley, there could still be storm slabs and wind slabs that have not bonded yet. As mentioned above, there could be buried surface hoar under Monday night’s snow and extra caution is advised for anyone getting out in this area. Triggering a slab avalanche up to 2′ deep could be possible. There are also deeper weak layers that are still causing large avalanches, more on that below.

Only 6″ of new snow from Monday night at Turnagain Pass. This photo was taken on Tincan looking up drainage and toward Sunburst yesterday, 2.22.22.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • 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.
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

Weak layers surrounding various crusts buried deeper in the snowpack are still a concern. This is in addition to some weak snow formed just before Valentine’s Day that is now buried several feet deep in the Girdwood area; we are calling this the Valentine’s Day layer and appears to be more of a concern in Girdwood Valley. The large avalanche in Crow Creek yesterday on the Goat Shoulder tells us we can’t underestimate what these buried layers can do. We hope to get a closer look at that avalanche today.

The south end of the forecast zone (for example, Silvertip area) and further out of the advisory area in Summit Lake, are also areas we have seen avalanches break in old weak layers. How this next series of storms impacts those layers will be telling. That all said, we need to be very conservative in these zones. During the stormy weather coming up, we need to give runout zones a wide berth.

Weather
Wed, February 23rd, 2022

Yesterday:  Mostly to partly cloudy skies were over the region. A few lingering snow flurries were seen in the morning as the last storm moved out. Ridgetop winds were 5-15mph from the east with some gusts to 30 early in the day. Temperatures remained warm, 35-40F at lower elevations and low 20’sF at the high elevations.

Today:  Windy and mostly cloudy. Another round of storms is headed in today that look to last through the weekend. Increasing easterly ridgetop winds will be ahead of the snow and blow 30-40mph with stronger gusts before bumping up further tonight. Light snow should begin in the afternoon with heavier snowfall seen tonight (trace today, 3-6″ overnight). With the warm temperatures, the rain/snow line looks to sit between 300-800′.

Tomorrow:  Heavier snowfall is expected for Thursday into Friday with associated strong east winds. If thing line up right, we’ll be measuring in feet (2-3′ by Friday possibly). The rain/snow line should reach 1,000′, but hopefully not higher. Stay tuned!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30 0 0 94
Summit Lake (1400′) 28 0 0 45
Alyeska Mid (1700′) 29 tr tr N/A

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21 E 10 33
Seattle Ridge (2400′) 24 SE 12 30
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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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