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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, January 12th, 2021 - 7:00AM
Expires
Wed, January 13th, 2021 - 7:00AM
Forecaster
Andrew Schauer
Avalanche Warning
Issued: January 12, 2021 6:00 am
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

We have extended the Backcountry Avalanche Warning issued through the National Weather Service through tomorrow morning. Recent heavy snowfall and continued accumulation today will keep the avalanche danger HIGH in the mountains surrounding Turnagain Pass, Girdwood Valley, Portage Valley, Summit Lake and the Seward/Lost Lake/Snug Harbor zone. It is very likely a human could trigger a very large avalanche, and it is likely that we will see large natural avalanches as well. These avalanches may run far into lower elevation runout zones in the valley bottoms. Travel in and below avalanche terrain is not recommended today.

Roof Avalanches: Several large roof avalanches have occurred since Sunday, and may continue to occur today. Be aware of overhead hazards as you go in and out of buildings, and keep an eye on children and pets.

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Tue, January 12th, 2021
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
High (4)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
High (4)
Below Treeline
Below 1,000'
Avalanche risk
High (4)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Johnson Pass area: There was a report yesterday of a large natural avalanche in the Center Creek drainage near Johnson Pass that ran far into the valley bottom.

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

As snow continues to pile up, avalanche conditions remain very dangerous. Since the storm began on Wednesday, we have now received 6-7’ of snow, equal to 8.4” snow water equivalent (SWE) at Turnagain Pass, and up to 7-8’ snow equaling close to 10” SWE near Girdwood. This includes around 1.5-2’ of snow equaling 2” SWE since yesterday morning, and several periods of rain up to around 1600′ in the past few days. For events like this, the avalanche danger is crystal clear. Until the snowpack has some time to adjust this load, very large human-triggered avalanches are very likely, and travel in or below avalanche terrain is not recommended. We have already seen evidence of large natural avalanches occurring during this storm cycle, and we will most likely continue to see large avalanches running far into lower-elevation runout zones until after the storm subsides.

Click here for a link to a video summarizing the conditions in Turnagain Pass.

The snow keeps piling up and signs are starting to get buried at Turnagain Pass. 01.11.2021

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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 have been tracking a layer of faceted snow associated with the 12/1 rain crust, which is now buried around 8’ deep, and exists at elevations up to around 2500’. The heavy load from this storm cycle will increase the chance we could see very large avalanches failing on this layer. This is kind of a side note right now, since the storm slab avalanches mentioned above are so dangerous.

Weather
Tue, January 12th, 2021

Yesterday: Continued heavy snowfall yesterday brought 15-20” snow equal to 1.5-2” SWE. Ridgetop winds were blowing 20-30 mph out of the east with gusts in the high 40’s. Temperatures hovered in the mid-to upper 20’s F at higher elevations and in the low 30’s F at low elevations. The rain line dropped down to around 500’ during the day, with snow to sea level overnight.

Today: Snow will gradually taper off during the day, with another 6-10” expected by this afternoon. Winds are expected to slow down through the day, with ridgetop speeds of 10-15 mph out of the east, and gusts around 25 mph. Temperatures will be in the low 20’s F at upper elevations, and in the upper 20’s F at low elevations. Clouds are expected to break up slightly through the day, with a chance of some pockets of blue sky poking through this afternoon.

Tomorrow: Light snowfall overnight may produce another 2-4” new snow, with easterly ridgetop winds around 15 mph and gusts to 20 mph. Low temperatures tonight are expected to be in the high teens F at upper elevations to mid 20’s F at low elevations, with highs in the mid- to upper 20’s F tomorrow. Snow showers may linger through the day, and it looks like our next round of heavy snowfall will be later in the day Thursday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 21 2.1 133
Summit Lake (1400′) 31 4 0.4 32
Alyeska Mid (1700′) 31 20 1.6 124

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21 ENE 22 46
Seattle Ridge (2400′) 25 N/A N/A N/A

*Seattle Ridge anemometer is rimed over.

Observations
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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.