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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, February 25th, 2021 - 7:00AM
Expires
Fri, February 26th, 2021 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE today. With new snow and an overnight wind shift from east to west, it will be possible to trigger fresh wind slabs in wind-loaded terrain on all aspects. Watch for blowing snow, look for signs of wind effect and loading. In addition there are buried weak layers, 1-3′ deep in the snowpack, that may still be triggered on steep slopes. Assess the snowpack as you travel, identify areas of concern and evaluate terrain consequences.

SUMMIT LAKE/SNUG/LOST LAKE/SEWARD:  As usual the west/northwest winds are forecasted to be stronger in the central and southern Kenai Mountains. With this there is the potential for natural wind slab avalanches in these areas again. Extra caution is advised.

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Thu, February 25th, 2021
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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

With sunshine in the forecast today travel into the Alpine will be appealing. Keep in mind triggering a fresh wind slab around a foot deep will be possible. Yesterday there was steady snowfall throughout the day with 2-6″ of accumulation, favoring Girdwood. With this there were easterly winds that were sustained at ridgetops, 15-25 mph with gusts into the 30s and 40s. Blowing snow and fresh wind slab formation was observed. In the evening the snow shut off and the winds shifted to the west/northwest blowing 10-15 mph with gusts into the 30s. These are forecast to continue throughout the day peaking in the late afternoon. Today wind slabs will be possible on all aspects. Figuring out which slopes are loaded might be complicated. The east winds impact Turnagain terrain more significantly than the west/northwest winds. However, it is important to remember west/northwest winds can funnel through the Pass from the south and load north aspects on the non-motorized side, while at the same time load the SE face of Seattle Ridge. This wind pattern also increases through channeled terrain and can be more pronounced in Crow Pass and Portage. Pay attention to blowing snow and active wind-loading.  There may also be old lingering wind slabs from the past wind-loading events as well. Look for smooth pillowed snow on convexities, cross-loading in gullies and feel for stiff snow over softer snow. As always, watch for signs of instability like shooting cracks from your skis or machine.

If you do find and trigger a new wind slab, remember it could step down to old buried weak layers deeper in the snowpack. In this case, a larger avalanche is possible (more on this in Problem 2).

Cornices: When traveling along ridgelines be sure to give cornices plenty of space, and minimize the amount of time spent traveling below them. Cornices could fail under the weight of a person on skis or a snowmachine, and might trigger an avalanche if the slope below is wind-loaded.

Sluffs: It will be easy to trigger loose snow avalanches (sluffs) in steep terrain that has been sheltered from the winds. It is unlikely an avalanche like this would be big enough to bury a person, but they can have serious consequences if they carry you into terrain traps like cliffs, rocks, or trees.

 

Cracking on a wind-loaded small slope yesterday, 2.24.21 on Eddies. Watch for cracking and drifted snow today.

For video click HERE.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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

We continue to track two weak layers of snow (surface hoar and facets) buried in the top 2-3′ of the snowpack. You may be feeling a bit of message fatigue as we have been talking about these layers for close to a month. However, the data continues to point to the potential for these layers to fail and cause an avalanche. There have been avalanches in the past week that have failed on these layers and snowpack test continue to show instability. We know these layers are present in most areas and in all the elevation bands, but they are not reactive everywhere, which makes it complicated. The new snow and wind-loading could add a little more stress to the snowpack. There may be old hard wind slabs sitting on top of the weak layers allowing you to get well out onto the slope before it fails or failing after other machines or skiers have have already ridden the slope. Triggering a fresh wind slab or cornice fall may step down to one of these buried weak layers. As we have said before, this snowpack has to be viewed with some uncertainty and caution.  If choosing to push into steeper terrain, keep in mind that these weak layers exist, watch for signs of instability (with the caveat that they may not be present but the slope may be unstable), follow safe travel protocol and evaluate terrain consequences.

Snow pit at 1200′ on Eddies, 2.24.21. Note the buried weak layers and that they propagated easily with not much force.

Snow pit @ 2000′ on Eddies, 2.24.21. This was in a spot with wind hardened snow above a layer of buried surface hoar. The extended column test took more force but still showed potential for an avalanche to be initiated, ECTP23.

Additional Concern
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

On steep southerly slopes especially at lower elevations expect roller balls and small natural wet loose sluffs as sun hits the new snow. The colder northwest winds may keep things cool in the Alpine but wind protected rocky areas in the direct sun may also see some activity. The roller balls and small wet loose sluffs could also be human-triggered if you find yourself traveling in steep southerly terrain. It’s that time of year where aspect in relation to solar gain will start to play a role in avalanche conditions. Keep that in mind as the we move into March!

Weather
Thu, February 25th, 2021

Yesterday: Skies were cloudy with snow falling throughout the day, 2-6″ of accumulation, favoring Girdwood. Rain at sea level. Winds were easterly 15-25 mph with gusting into the 40s and 50s. Temperatures were in the mid 30°Fs at sea level and in the low 20°Fs to high teens in the Alpine. Overnight skies cleared. Winds shifted to the west, 10-15 mph with gusts into the 30s. Temperatures slowly dropped and were in the low teens at upper elevations and high 20°Fs at sea level.

Today: Skies will be mostly sunny. Winds will be west/northwesterly 15-25 with gusts into the 30s, possible higher in the late afternoon. Temperatures will be in the teen to low 20°Fs in the Alpine and mid 30s at sea level. Winds will ease in the overnight and switch the east. Clouds build becoming mostly cloudy by early morning Friday with light snow showers possible. Overnight temperatures will be in 20°Fs.

Tomorrow: Skies will be mostly cloudy with snow likely. Winds will be easterly increasing throughout the day. Temperatures will be in the 20°Fs at upper elevations and 30°Fs at sea level. The pattern looks to remain active through the weekend. There is some uncertainty with storm tracks but according to the NWS, “Bottom line, there is a good chance we could see more significant precipitation this weekend.” Fingers crossed!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 27 2 0.2 114
Summit Lake (1400′) 27 1 0.1 43
Alyeska Mid (1700′) 26 5 0.44 117

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 NE-NW* 16 52
Seattle Ridge (2400′) 21 E-W* 6 20

*Winds were easterly for around 12 hours and then swung westerly for the next 12 hrs.

Observations
Recent Observations for Turnagain Pass
Date Region Location
04/12/21 Turnagain Observation: Tincan
04/10/21 Turnagain Observation: north sides
04/09/21 Turnagain Observation: Girdwood to Turnagain Road Observations
04/05/21 Turnagain Avalanche: Resort bowl Seattle creek head wall
04/04/21 Turnagain Observation: Center Ridge
04/03/21 Turnagain Observation: Repeat Offender – Seattle Ridge
04/02/21 Turnagain Observation: Seattle Ridge
04/01/21 Turnagain Observation: Pete’s
03/31/21 Turnagain Observation: Tincan
03/30/21 Turnagain Observation: Eddies
Riding Areas
Updated Thu, April 01st, 2021

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Open
No parking in turnaround at end of the road near the outhouse.
Placer River
Open
Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Skookum Drainage
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
Turnagain Pass
Open
Twentymile
Open
Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Seward District
Carter Lake
Open
Lost Lake Trail
Open
Primrose Trail
Open
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season.
Snug Harbor
Open
South Fork Snow River Corridor
Open
Summit Lake
Open

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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.