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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, February 22nd, 2024 - 7:00AM
Expires
Fri, February 23rd, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Heavy snowfall last night and windy weather today will keep the avalanche danger CONSIDERABLE above 1,000′. Wind slab avalanches between 1-2′ thick may release naturally and should be easy for a person to trigger. These could be larger than expected if they break in a weaker layer in the snowpack. A conservative mindset is recommended.

The danger is MODERATE below 1,000′ where a hard crust has formed under 4-8″ of new snow. It will be possible to trigger small avalanches in the new snow.

SUMMIT PASS / SNUG HARBOR / SEWARD:  Most areas on the Kenai saw heavy snowfall last night. Human triggered avalanches will be likely on slopes with over 10″ of new snow and especially those loaded with windblown snow.

Special Announcements

AK DOT&PF:  There will be intermittent traffic delays Thursday, February 22 on the Seward Highway for Avalanche Hazard Reduction work. Closure will be in place at the Seward – Sterling Wye from milepost 39 to milepost 36.5 on the Seward Highway. Motorists should expect delays of up to 45 minutes between 10:00 AM and 12:00 PM. Updates at 511.alaska.gov.

Friday night in Seward!
Forecaster Chat, 5-6 pm at the Community Library and Museum room
. For our friends in Seward and Moose Pass, come chat with us about the product we are producing called the “Weekend Avalanche Outlook”. We’ll also be talking about the state of the snowpack in Summit and Seward, and any other questions you have. More info Here.

Thu, February 22nd, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Fri, February 23rd, 2024
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
Fri, February 23rd, 2024
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
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.
Recent Avalanches

With a short break in clouds yesterday morning, several folks noted older piles of wet debris in avalanche paths from the rainy and windy storm on Tuesday. That storm rained as high as 2,000′ and the wet snow is freezing into a crust. As skies clear this morning, anywhere from 4-10+” of new snow from last night should be sitting on that crust up to the top of treeline. If you get out today, we’d love to see any photos of what you find. Natural avalanches were likely occurring last night. Thanks!

Avalanche Problem 1
  • 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

Last night’s weather event brought heavy snowfall for several hours to many areas. Check out the ‘estimated’ snow totals below. Although rain was falling at sea level, this switched to snow early this morning as cooler temperatures are moving in. The storm is exiting now and skies should clear through the day. Ridgetop winds are switching to the west and should blow in the 15-20 mph range with gusts in the 30s. New snow plus wind equals a wind slab avalanche issue.

Estimated snowfall totals at the mid-upper elevations:

Girdwood:  6-12″
Turnagain:  6-10″
Portage/Placer:  10-15″
Summit Pass:  6-8″
Seward/Lost Lake:  14 – 24″

New Wind Slabs:  If you are headed out, keep any eye out on the peaks in case there is snow being transported by the west winds. Watching for active wind loading will be one of the best red flags to look for. After this, watching the snow surface for other signs like stiffer snow over softer snow and cracks that shoot out from you. Note: the winds from the storm were easterly, so wind slabs from last night will be on different aspects than new slabs formed by today’s west winds. Either way, on slopes steep enough to slide, if there is a wind slab it should be easy to trigger. At elevations above 2,000′ there could be a chance a wind slab breaks in an older weak layer. If this occurs it would create a much larger and dangerous avalanche.

With a lot of uncertainty after a week+ of stormy weather, a very cautious mindset and careful snowpack evaluation is recommended. To avoid all avalanche issues, we can stick to those lower slope angles below 2,000′ where new snow sits on a crust.

SUNSHINE:  If the sun makes an appearance today, watch for solar triggered moist snow sluffs on steep southerly slopes. These could trigger a shallow storm slab or wind slab.

 

Sunburst ridge yesterday before last night’s storm. Big thanks to those for writing in and sending us photos! 2.21.24.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Aspect/Elevation
  • 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.

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

A big question mark moving forward is how dangerous that weak layer is from January. It is buried 1.5-3′ deep now and was the layer responsible for the avalanche accident on John Mt. After such an onslaught of rain up to 2,000+’ on Tuesday, which was the most concerning elevation band for that weak layer, the story may be coming to an end. This is because the rain saturated the top of the snowpack, is freezing into a crust, which can quickly stabilize the snowpack at those mid elevations. What about the higher elevations? Those slopes with the least amount of wind damage will be a place that a weak layer could remain and a surprise avalanche could occur.

These are all things we’ll continue to assess. Because faceted layers are guilty until proven innocent we’ll continue to be wary.

Weather
Thu, February 22nd, 2024

Yesterday:  Patches of sunshine poked through in the morning before the next storm pushed in later afternoon. Through the daylight hours, only a trace of new snow was seen with increasing easterly winds. Overnight heavy snowfall ensued with 4-10″ in the higher elevations from Girdwood, Turnagain and Summit Passes (12-18″ in Portage and Seward high elevations). Easterly winds peaked with the snowfall, averaging 30-40 mph and gusts in the 80s.

Today:  The storm that peaked overnight is exiting today with clouds beginning to clear. Ridgetop winds are shifting westerly this morning and should blow 15-20 mph with gusts in the 30s. Temperatures will remain cool, generally in the 20s F.

Tomorrow:  A few clouds are supposed to move in Friday with the chance for a few snow flurries. Ridgetop winds look to decrease and turn more southerly (5-10 mph gusting 25 mph). The weekend looks like colder air will stream in from the north with partly cloudy skies. Right now the northerly (outflow) winds look generally light, but stay tuned as this could change.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28 4 0.4 91
Summit Lake (1400′) 30 5 0,4 44
Alyeska Mid (1700′) 29 5 0.4 94
Bear Valley – Portage (132′) 35 2 0.85
Grouse Ck (700′) 33 14 n/a 74

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 ENE 30 82
Seattle Ridge (2400′) 23 n/a n/a n/a
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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.