Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, December 8th, 2021 - 7:00AM
Expires
Thu, December 9th, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE on all aspects above 1,000′. Human triggered wind slab avalanches (1-3+ feet deep) will be likely on any slope with recent or active wind loading. Additionally, large and dangerous slab avalanches could be triggered by people, or a smaller wind slab, in weak layers that are now buried 3 to 5 feet deep. These large slabs are predominantly occurring in the mid-elevations (between 1,500 and 3,000′) and could be deadly. A continued very cautious mindset is required as the snowpack remains unstable.

The danger is MODERATE below 1,000′ where cold temperatures are freezing the moist new snow from the Sun/Mon storm.

SUMMIT LAKE: Human triggered wind slabs as well as slabs breaking in buried weak layers are likely in the Summit area as well. With around 12″ of new snow slabs are expected to be 1-2′ thick.

SNUG HARBOR/LOST LAKE: A very dangerous snowpack has set up in these areas as 2-3′ of new snow is sitting on older weak faceted snow. The strong NW winds last night have added to the dangerous conditions. Heads Up- large human triggered avalanches are likely in this zone, especially closer to Snug Harbor.

 

Special Announcements
  • A Winter Storm Watch has been issued by the NWS for tomorrow (Thursday) for a storm that could bring another 10-20 inches of snow.
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Wed, December 8th, 2021
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

There were several natural avalanches that occurred again yesterday, however not nearly as active as things were on Monday. Visibility was slightly better, but the skies never quite cleared enough for a great look around. Here’s what was seen:

Eddie’s lower rollovers:  6+ new natural slab avalanches on the lower Eddie’s rollovers at elevations between 1,500 and 2,000′. Slabs appear to be 3-5′ in depth, 100-400′ wide, and likely failed in faceted snow over the Halloween crust.

Pyramid Peak, NE face:  One large natural avalanche that occurred around 3pm yesterday that sent debris to sea level.

Various paths along Turnagain Arm: There were reports of other paths along Turnagain Arm that saw natural avalanche activity yesterday.

North End of Summit:  Several natural avalanches seen as well a remotely triggered avalanche that broke in weak snow above the Halloween crust.

Fresno in Summit Lake:  Three natural slab avalanches near 2,000′ in elevation. Slab depth 1-2′ and likely released on weak snow associated with the pre-existing snowpack.

Summit Peak in Summit Lake:  One wind slab avalanche occurring near the ridge that was large enough to send debris to where the slope angle lessens.

Eddie’s lower rollovers with arrows pointing to several of the natural slab avalanches seen yesterday. 12.7.21.

 

Debris below the NE face of Pyramid Peak seen from across Turnagain Arm. Avalanche occurred around 3pm yesterday. 12.7.21.

 

New natural slab avalanches on Fresno in Summit Lake. Photo: Paul Wunnicke, 12.7.21.

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Almost 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.

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

Today is again a day to be on our guard and be suspect of any slope near 35 degrees or steeper, even those slopes at the mid-elevations in the trees, such as the ones in the photo of Eddie’s and Fresno. Although natural avalanches are not likely today, human triggered avalanches are. These could be wind slabs or deeper slabs.

A brief break between storms is expected today with some breezy northwest winds. Skies should be fairly clear this morning with some high clouds headed in later this afternoon. The cold northwest winds that picked up yesterday really got cranking last night in some areas. Two of the stations that pick up this wind direction are rimed over from the wet storm, and Sunburst doesn’t do a great job with the northwest flow. The station that does is above Grandview called AKRR Mile 43. This station recorded 25-35mph winds with gusts near 60mph last night.

That said, there could be many new wind slabs from overnight, others from yesterday, and even wind slabs from the easterly winds during the storm event Sunday through Monday. With anywhere from 1-3′ of snow from that storm (including soft snow below), wind slabs could range from 1-3+ feet thick. We can watch for those tell tale signs of wind deposited snow; stiffer snow over softer snow, cracking in the snow around you and any whumpfing (collapsing). However, what’s below the wind slabs is even more concerning – those weak layers. Wind slab avalanches could step down and trigger a larger much more dangerous avalanche. This begs the question, do we really want to take that risk today? Or better yet, let the snowpack keep adjusting and stick to the lower slope angles for a fun day without these tricky, and potentially deadly, avalanche issues.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Almost 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.

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 weak faceted snow and buried surface hoar that was formed in mid-November is now buried anywhere from 3-5′ deep at Turnagain Pass and Girdwood and 1-2′ deep in the Summit Lake zone. As these layers get deeper, they could be getting harder for us to trigger. But, the fact that all those rollovers on Eddie’s released less than 2 days ago, and there could be others we just have not had the visibility to see yet, tells us they are still a real problem.

The hard thing is we may not get any sign of instability before a slope avalanches. More people could ride or ski a slope, and the snowpack could ‘feel fine’, before someone finds the thin spot and it releases. Stability tests were already becoming unreliable last week and likely more so now. And lastly, the nature of remote triggering. We could trigger these from the top, sides or below a slope. This could put others in danger if someone triggers a slab from the ridge. All things to think about as we move forward.

Elevations and these weak layers: Most of these persistent slab avalanches to date have been between 1,500 and 3,000′. This coincides in many cases with the elevation of the Halloween crust under the faceted snow (the crust extends to around 2,500′ at Turnagain and even 3,000′ in Girdwood). Seeing these slabs release as low as 1,500′ should really clue us in to being careful with our slope angles in the trees- especially those areas that have seen little traffic this winter.

Snowpack structure above the Halloween crust at 2,200′, SE facing slope, on Tincan from yesterday. Total snow depth was 7 feet, snow depth above the Halloween crust was 4 feet.

Weather
Wed, December 8th, 2021

Yesterday:  Mostly cloudy skies hung over the region with some very light snowfall (trace to a couple inches). The NW ridgetop winds picked up somewhat during the day, but appeared to have blown more overnight in the 20-30mph range with gusts in the 50’s in places. Temperatures have dropped down to the single digits overnight with the cold air moving in from the north.

Today:  Mostly clear skies this morning transitioning to cloudy by this evening. The NW winds have backed off this morning, but are still slated to be in the 10-20mph range through the day. Temperatures are forecast to remain chilly, single digits to the low teens at all elevations.

Tomorrow:  Another system heads in tomorrow morning with increasing easterly winds a chance for 10-20″ of snow by tomorrow night. The higher amounts in Portage and less so inland near Summit Lake. Right now, temperatures look to remain just cold enough for mostly snow to sea level.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 25 1 o.1 70
Summit Lake (1400′) 23 1 0.1 24
Alyeska Mid (1700′) 21 1 0.1 46

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 14 NW 6 27
Seattle Ridge (2400′) 16 N/A* N/A* N/A*

*Seattle Ridge wind sensor is rimed over.

Observations
Recent Observations for Turnagain Pass
Date Region Location
11/28/22 Turnagain Observation: Pastoral
11/27/22 Turnagain Avalanche: Tincan
11/26/22 Turnagain Observation: Eddies
11/26/22 Turnagain Observation: Eddies
11/26/22 Turnagain Observation: Lipps
11/25/22 Turnagain Observation: Sunburst
11/25/22 Turnagain Observation: Sunnyside / Seattle Ridge
11/25/22 Turnagain Observation: Sunburst
11/25/22 Turnagain Observation: Tincan Trees
11/25/22 Turnagain Observation: Tincan
Riding Areas
Updated Sun, November 27th, 2022

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
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Placer River
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Skookum Drainage
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Turnagain Pass
Closed
The Forest has issued a closure order for Turnagain Pass due to inadequate snow cover for resource protection. Conditions will be monitored daily. Between 16-20” of snow exists at the parking lot. The scheduled opening would have been the Wednesday before Thanksgiving per Forest Plan.
Twentymile
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Seward District
Carter Lake
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Lost Lake Trail
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Primrose Trail
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Resurrection Pass Trail
Closed
Closed to motorized use for the 2022/23 winter season per Forest Plan. Open next season.
Snug Harbor
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
South Fork Snow River Corridor
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Summit Lake
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.

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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.