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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, February 8th, 2024 - 7:00AM
Expires
Fri, February 9th, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

A storm is moving in today and peaking tomorrow, which will create dangerous avalanche conditions. Today the danger is CONSIDERABLE above 1,000′ where increasing winds are expected to blow snow into fresh wind slabs 1-2′ deep. Natural wind slab avalanches could occur and should be easy to trigger by a person. Additionally, a person could trigger a slab avalanche 12-18″ deep in areas sheltered from the winds; this issue is most prominent in Girdwood and Placer Valleys.

*Tomorrow, the danger is expected to rise to HIGH due to 1 to 2 feet of new snow falling with strong winds. A Winter Weather Advisory has been issued by the National Weather Service that begins at 6pm this evening.

Special Announcements

Tonight! Feb 8, 5-6pm, at Peninsula Powersports in Soldotna – Forecaster Chat. Come by and meet the new forecasters, talk about the state of the snowpack in Summit and Lost Lake, and hear about our “Avalanche Weekend Outlook,” a new forecasting tool we started publishing this year for Summit and Seward!

SnowBall 2024:  Valentine’s Day, Feb 14 (7-11pm @ 49th St Brewing). The evening promises costumes, finger food, a rocking band, silent auction, and of course plenty of great company. Join us in supporting Chugach Avy as well as the Alaska Avalanche School. Details and tickets HERE.

Thu, February 8th, 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 9th, 2024
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
Fri, February 9th, 2024
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.
Recent Avalanches

We do not know if any new avalanches occurred yesterday during the cloudy and windy weather. The last known avalanches were from Saturday through Monday when a couple wind slabs were triggered as well as soft slabs in sheltered areas 12-18″ deep. These likely failed on weak snow formed in January.

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

After several days of small weather fronts bringing moderate to strong easterly ridgetop winds and just a few inches of new snow, there is a larger storm approaching today that will peak tomorrow. Until the snow starts to pile up late tonight, it will be the winds (easterly 15-20 mph gusting 40-50) that will be driving the avalanche bus.

Hence, another round of fresh wind slabs are expected to form today on any exposed slope and in most areas in the higher terrain. These slabs could be 1-2′ deep and sitting on weak snow, making them more reactive than your typical wind slab. Even though there have been several windy days, I’m guessing the winds will still find enough loose snow to create new wind slabs. Paying attention to what the winds are doing will be key. Avoiding any slope with active wind loading, staying out from under big slopes that might be getting loaded from above, and sticking to the lower angle sheltered terrain (30 degrees or less) will be a good bet for a fun day without avalanche issues.

Graphic below shows the expected snowfall totals for tomorrow, Friday. Add to these numbers 4 to 6 inches, that is what is expected tonight.

Big thanks to the National Weather Service for producing these snow and avalanche guidance products. If you don’t have it bookmarked yet, here is the link to their avalanche page.

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

Friday’s storm will be the first significant snowfall in a month that Turnagain Pass and the surrounding mountains have seen. Unfortunately, there is a weak layer it will be loading and avalanche conditions could become very dangerous in the foreseeable future. The weak layer is from the January cold and dry spell and is a mix of faceted, sugary snow, and buried surface hoar. This will be an issue at all elevations, including lower elevations and slopes that are sheltered in the trees – something to clue into if headed out for some storm skiing/riding.

For today, before the snowfall, anywhere from 8-18″ of snow currently sits on this January weak layer in sheltered areas. It has produced a couple small avalanches so far on steep rollovers. Watch for these steep sections in the trees as well as exposed areas in case you trigger one of these slabs. As always, red flags like cracking and whumpfing/collapsing in  the snowpack are bulls eye clues for unstable snow.

Check out Mik’s video from Carter Lake yesterday. This area is in the central Kenai Mtns, but this setup is very similar to the forecast zone and many areas region-wide.

 

 

Snowpit from lower elevations in the Placer Valley zone (Skookum drainage). Note the sugary facets. This layer could start producing large avalanches if it gets loaded with another 2 feet of new snow, which is the amount expected by Friday night. 

Additional Concern
  • Glide Avalanches
    Glide Avalanches
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.
More info at Avalanche.org

Glide avalanches are still a concern on any slope with glide cracks present. We have not seen or heard of one releasing into an avalanche for two weeks now, but that doesn’t mean a crack can’t release today. Continuing to avoid any time under glide cracks is prudent.

Weather
Thu, February 8th, 2024

Yesterday:  A windy and cloudy day was seen yesterday with a few snowflakes here and there. Portage Valley picked up 2-4″ of new snow but otherwise, only a trace was seen. Ridgetop winds were 10-15mph from the east with gusts in the 30 to 40s.

Today:  A storm is moving in today that will bring increasing ridgetop easterly winds and a few inches of new snow by tonight. Ridgetop winds should average 15-20mph with gusts near 40 or 50 today and increase overnight tonight. Temperatures will remain in the 20s at the mid and upper elevations.

Tomorrow:  The storm looks to peak on Friday morning with between 12-24″ of new snow falling by Friday night. The rain/snow line could creep up to 1,000-1,400′ as warm air funnels in from the Gulf. Ridgetop winds will be strong from the east/southeast, 30-40 mph with gusts near 80 mph. Another system is right on the heels for Sunday so stay tuned!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28 0 0 79
Summit Lake (1400′) 24 0 0 n/a
Alyeska Mid (1700′) 28 0 0 83
Bear Valley – Portage (132′) 34 tr 0.25
Grouse Ck (700′) 30 1 0.1 57

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20 E 13 45
Seattle Ridge (2400′) 23 SE 10 22
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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.