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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, February 5th, 2024 - 7:00AM
Expires
Tue, February 6th, 2024 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′ today. Strong easterly winds will build another round of sensitive wind slabs, making it easy to trigger an avalanche up to a foot deep within the new snow from the past few days. This will also be adding stress to the weak layer of snow that was buried a week ago, and may produce larger avalanches 2′ deep or deeper. Those deeper problem layers are more difficult to identify, and the best way to manage the problem is to avoid steep slopes and give the snow more time to adjust to the new load. The danger is MODERATE below 1000′, where the same concerns exist but lighter winds will make avalanches a little less likely.

Special Announcements

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.

Mon, February 5th, 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
Tue, February 6th, 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
Tue, February 6th, 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

Yesterday we received information about a skier that was caught and carried in a wind slab avalanche on Raggedtop on Saturday (Feb. 3). The avalanche was relatively small (6″ deep on average and 30 ft wide), but it ended up running 700 vertical feet and carried the skier a short distance before they were able to self-arrest. More details in this observation. Skiers at Turnagain Pass also noticed some natural avalanche activity within the new snow at multiple locations.

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

We are expecting another quick-moving system to pass through the area today, with winds arriving before the snow starts to fall again this afternoon. We saw easterly winds start to pick up in the early hours this morning, and are anticipating average speeds of 20 to 35 mph with gusts of 30 to 40 mph through the day. Models are showing high wind speeds dipping down into the lower elevations, so we are expecting to see reactive wind slabs forming down into our treeline elevation band. There is currently anywhere from 6 to 12″ or more of light and fluffy snow on the surface, so the winds will have plenty of slab-building material to work with during the day. These fresh slabs will be adding stress to the weak faceted snow that was buried a week ago and will have the potential to make bigger avalanches today. More on this in Problem 2 below.

The most likely places to trigger an avalanche will be just below ridgelines, in steep gullies, and on the downhill side of convex rollovers. Usually a wind slab problem can be easy to assess by digging quick hand pits as you travel and looking for relatively stiff snow sitting on top of relatively soft snow. Keep in mind, the slab doesn’t necessarily need to be pencil-hard to produce an avalanche – the most sensitive wind slabs are often fairly soft. Slope cuts on short but steep terrain features can be a great way to quickly assess surface problems like wind slabs. Be aware of steep terrain overhead today, since we may see some natural avalanches releasing as the winds blow through the day.

Avalanches similar to this snowboard-triggered wind slab on the Library will be easy to trigger as the winds blow today. This avalanche carried a person several hundred feet before they were able to ride off the moving debris pile. Photo submitted anonymously, 02.02.2024

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

The three weeks of dry and cold weather in January formed a weak layer of faceted snow that was buried when snow returned to the area last week. This interface was the likely culprit for two human-triggered avalanches that involved people being caught and carried over the past three days. One was on Friday in the Library on Tincan Ridge (details here), and the other was on Raggedtop on Saturday (details here).  These two human-triggered avalanches failed where the wind had drifted snow into thicker slabs, which were able to propagate a fracture.

This weak interface remains a concern for today. The most likely terrain to run into trouble will be anywhere there is a stiffer slab in the upper snowpack. With multiple rounds of alternating snow and winds, these slopes may be difficult to recognize without digging into the snow. Because surfaces were so variable before the snow started falling, it is likely this problem has a spotty distribution and some slopes may be perfectly safe while others are just waiting for a person to come along and trigger an avalanche.

From what we have seen so far, the weak layer may be the most developed at lower elevations, but the slabs are stiffest at higher elevations. When we’re dealing with a tricky problem with a complicated distribution, the best way to manage the problem is to step back from steeper terrain and give this snow some time to adjust.

 

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

We’ve seen an unusually active glide cycle since late December and for over three weeks now, we have listed glide avalanches as our first or second avalanche problem. This will be the first time we’ve bumped it down to an additional concern, but we’re still paying attention to it. We haven’t noticed any glide avalanches release since the last big one hit the motorized uptrack on the front side of Seattle Ridge last Friday (Jan. 26). Multiple rounds of snow have made these harder to recognize, which makes for the added potential of falling into an open glide crack as well as the avalanche hazard this problem poses. It is impossible to say whether this problem has entered a dormant spell for now, or if it will wake right back up again. Regardless of the most recent activity, it is always a good idea to avoid spending any time below open glide cracks and to move quickly if you cannot find an alternate route.

This glide crack on Eddie’s was completely buried and impossible to recognize- until I broke through the snow on the surface and fell in. 02.04.2024

Weather
Mon, February 5th, 2024

Yesterday: Snowfall continued for the first half of the day, with another 2 to 3” across most of the advisory area before clouds started breaking up in the afternoon. The snow line stayed down to sea level. Winds were light for most of the day, but have picked up overnight and have been blowing 10-20 mph out of the east for the past few hours. High temperatures were in the low 20s F with lows in the single digits to mid teens F.

Today: We should see another quick moving storm passing through today, with wind being the main factor for most of the daylight hours. Easterly winds are expected to average 20 to 35 mph with gusts of 30 to 40 mph, and it is likely that some of these stronger winds will dip down into lower elevations during the day. Snowfall should pick up again this afternoon, with 1 to 2” expected for most areas during the day and another 1 to 2” just after sunset. Portage and Placer could see closer to 6-10” by tonight. We might see mixed rain and snow up to around 200’. High temperatures should be in the mid to upper 20s F with lows in the mid teens to 20 F.

Tomorrow: Things are expected to quiet down tomorrow with partly cloudy to mostly sunny skies and light westerly winds of around 5 mph. High temperatures should be in the low to mid 20s F with lows in the mid teens to 20 F. No precipitation is expected.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 18 2 0.2 81
Summit Lake (1400′) 16 1* 0.1 N/A
Alyeska Mid (1700′) 15 2 0.18 87
Bear Valley – Portage (132′) 13 2 0.18
Grouse Ck – Seward (700′) 18 0 0 56

*Estimate. Snow depth sensor is down.

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 17 ENE 7 35
Seattle Ridge (2400′) 19 S 3 16
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.