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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, February 6th, 2024 - 7:00AM
Expires
Wed, February 7th, 2024 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. Triggering a slab avalanche around a foot deep is possible. The chances are more likely on wind loaded slopes but this could also happen on slopes that appear to not have been wind loaded. Over the weekend three of these types of avalanches were triggered with three people caught (all escaped). Conditions are similar today. Additionally, remember to avoid being under glide cracks in case they release into an avalanche.

Special Announcements

Chugach State Park:  A skier triggered two avalanches in the Falls Creek area on Sunday, check out the update on the CSP Outlook page.

Peninsula Powersports in Soldotna will be hosting us on this Thursday, Feb 8, 5-6pm. Come by and meet the new forecasters, talk about the state of the snowpack in Summit and Seward, and hear about our “Avalanche Weekend Outlook,” a new forecasting tool we started publishing this year for Summit and Seward!

SnowBall 2024:  Mark your calendars for 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 our friends at the Alaska Avalanche School. Details and tickets HERE.

Tue, February 6th, 2024
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Wed, February 7th, 2024
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
Wed, February 7th, 2024
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

There were no reported avalanches yesterday. However, over the weekend there were three human triggered avalanches with people caught and able to escape. Two of them (Tincan’s Library and Girdwood’s Raggedtop) were in our forecast zone and one just to the west in Falls Creek pictured below. The two avalanches in our forecast area were suspected to be wind slabs sitting on the weak snow from January. The Falls Creek avalanche appears to be settled storm snow sitting on weak snow from January. The common factor is the weak sugary (faceted) snow that formed during the January dry spell. More on that in Problem 2. A big thank you to all these folks for writing in and we’re grateful everyone is ok!

 

Skier triggered avalanche in Falls Creek from Sunday. Although this area is just to the west of our forecast zone in Chugach State Park, it is the type of avalanche we are concerned about in the Turnagain Pass area as well. Photo credit Mike Records, 2.4.24.

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

Clearing skies and a break in weather is expected today before another weak weather front moves in tomorrow. That front should bring clouds and 1-2″ of snow at best. Yesterday’s weather system was a bit more blow than snow. Around 1-3″ of snow fell in Girdwood, Placer, and Portage Valleys and just a trace at Turnagain Pass. The winds on the other hand were 10-15 mph and gusting near 40 from the east. Hence, another round of wind slabs were created yesterday. 

Wind Slab Avalanches:  On slopes in the higher elevations, or any exposed slope in the mid elevations, watch for signs of prior wind loading. There have been several wind events now and a variety of wind effected snow exists. Cracking in the snow around you, hollow feeling snow, and stiffer snow over softer snow are clues to look for. Watch for wind slabs to be cross loaded in gullies mid-slope and not just at the top of slopes. These slabs have the potential to break larger than expected due to the weak snow underneath from January.

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

Triggering what may seem like a surprise avalanche is possible on any slope steep enough to slide. That is because of a suspect weak layer anywhere from 10-20″ below the surface. This is the old surface from the January dry spell that is now a buried layer of sugary faceted snow. The layer is quite variable as to how weak it is and is something we are sussing out. The slab on top of it is also quite variable. Slopes with wind loading are clearly an issue as we’ve already seen avalanches, but areas without are also concerning. The warming temperatures can make this setup more reactive as well as the wind loading. Looking ahead, any new snow that slowly accumulates can also make this setup more worrisome. All that said, there is a lot of uncertainty as to how many slopes could produce an avalanche today and into the future. Watch closely for signs of instability (cracking and whumpfing).

Lower Elevations: I went over to Placer Valley yesterday to see what the lower elevation terrain looked like and found very weak facets under 12-16″ of settling soft snow (video below). For those headed to these areas, be suspect of steep slopes at these lower elevations as well as the higher elevations. Please keep us posted on what you find out there, good or bad.

 

 

Snowpit at the lower elevations in Placer Valley area. The weak sugary facets are pretty easy to spot in this pit.

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 over a week now, but that doesn’t mean one can’t pop off today. Continuing to avoid any time under these is prudent.

Weather
Tue, February 6th, 2024

Yesterday:  A quick frontal passage yesterday brought cloudy skies, snow flurries and warming temperatures. Between 1-3″ of snow fell in Girdwood, Portage and Placer Valleys while only a trace was seen at Turnagain Pass. Ridgetop winds were from the east averaging in the 10-15 mph and gusting near 40. Temperatures warmed to 37 F at sea level and into the 20s F in the higher elevations.

Today:  Partly cloudy to sunny skies with patches of valley fog is expected today. Ridgetop winds died off last night and should remain light and variable today. Temperatures look to stay in the 20s F at most locations.

Tomorrow:  Another weak front is moving through tomorrow, Wednesday. Models are showing 1-3″ of snow with ridgetop winds easterly, 10-15mph, gusting in the 20s. Temperatures remain on the warmer side, yet snow is expected to fall to sea level. Active weather should continue into the weekend. Stay tuned!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26 0 0 79
Summit Lake (1400′) 22 0 0 n/a
Alyeska Mid (1700′) 28 tr 0.02 85
Bear Valley – Portage (132′) 31 2 0.3
Grouse Ck – Seward (700′) 24 0 0 55

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 ENE 14 39
Seattle Ridge (2400′) 23 SE 8 18
Observations
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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.