Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, December 31st, 2022 - 7:00AM
Expires
Sun, January 1st, 2023 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger will start off MODERATE and rise to CONSIDERABLE above 1000′ today. Strong winds and heavy snowfall are expected to start midday which will quickly increase the avalanche danger and form wind slabs 1-2′ deep. The likelihood of human triggered and natural avalanches will increase throughout the day as the storm intensifies. Buried weak layers 2-4′ deep could produce larger avalanches at higher elevations. Below 1000′ the avalanche danger will start off LOW and rise to MODERATE. 

* Avalanche danger will rise to HIGH overnight tonight with very strong winds and heavy snowfall.

SEWARD / SNUG HARBOR / SUMMIT LAKE: Avalanche danger will rapidly increase across the region with the onset of a large storm midday Saturday. Conservative terrain selection and decision-making is recommended.

Roof Avalanches: With rain expected below 500′ today roof avalanches will become more likely. Remember to watch where you park and keep an eye out for kids and pets hanging out under roof lines with lots of snow left to slide off.

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Sat, December 31st, 2022
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

We received report of a wind slab releasing in steep terrain in main bowl on Seattle ridge yesterday. We think this avalanche likely released at the interface of the old snow surface and the Christmas storm snow. After the Christmas storm several large avalanches released on the south and east aspects of Seattle ridge and at lower elevation on the NW ridge of Magnum. Low visibility this week has made detecting recent avalanche activity challenging.

Wind slab avalanche triggered by snowmachiner on a west aspect at 3000′ in main bowl along Seattle Ridge. Photo Hunter McConnel 12.30.22

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Aspect/Elevation
  • 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.

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

As a large storm approaches today, increasing wind speeds will be the first thing to contribute to increasing avalanche danger. The combination of existing dry snow on the surface plus 6″ of new snow expected today will provide plenty of surface snow available to be transported into fresh wind slabs 1-2′ deep. The likelihood of human triggered and natural avalanche activity will increase throughout the day as more new snow falls and the wind speeds continue to increase. This morning winds are averaging 10-15 mph with gusts to 30 mph and by this evening we expect winds to average 50-75 mph with gusts of 100+ mph possible.

Wind slabs are most likely to be found along upper elevation ridgelines and cross loaded gullies. However, with very strong winds like we are expecting this evening you could find wind slabs in areas that are typically sheltered. To identify areas with fresh wind slabs look for active wind loading, hollow and stiff feeling snow, and shooting cracks on the surface. With conditions deteriorating throughout the day we recommend a conservative mindset and a quick bail out plan if visibility and travel conditions change quicker than expected.

Expected snowfall totals from Saturday at 6am to Sunday at 6am. Heavy snowfall should start between 12 pm and 3 pm on Saturday with winds ramping up prior to that. Graphic courtesy of NWS Anchorage 12.31.22

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Aspect/Elevation
  • 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.

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

With poor travel conditions and visibility this week we still have a lot of uncertainty about the status of our persistent weak layers at upper elevations. Prior to the Christmas storm, a layer of facets above the Thanksgiving melt freeze crust was causing collapses and concerning test results in portions of the forecast area with a generally thinner snowpack, like in Girdwood Valley and near the Johnson Pass trail. The rain and wet snow up to 2500-3000′ that came along with the Christmas storm has helped to stabilize these weak layers at middle elevations, but we have limited information on how the new load has impacted these persistent weak layers above 3000′. At this point we believe there is still a chance of triggering an avalanche on a persistent weak layer 2-4′ deep that could produce a very large avalanche.

In addition, we have seen some evidence of a weak interface between the old snow surface and the Christmas storm snow which could produce avalanches 1-2′ deep. With the addition of a new snow load and very strong winds today it is possible that these buried weak layers could become reactive again at upper elevations. Sticking to smaller terrain features and lower angle slopes is the best way to avoid buried persistent weak layers. Hopefully after the New Years storm we can get more conclusive information that these layers are no longer a concern, but for now they should stay on our radar.

Weather
Sat, December 31st, 2022

Yesterday: Broken cloud cover with occasional partly sunny skies and denser clouds towards the coast. Light to calm winds in the 5-10 mph range with gusts up to 20-30 mph overnight. Temperatures cooled slightly overnight but remain close to freezing at sea level and mid to low twenties at upper elevations. No significant new snowfall.

Today: A large storm is approaching today that will bring very strong winds and heavy snowfall. Wind speeds will increase from 10-15 mph with gusts of 20-30 mph this morning to averages of 50-75 mph with gusts up to 100 mph tonight. Winds should increase steadily this morning and be at full force from 6 pm Saturday to 6 am Sunday. Light snowfall is expected in the morning, increasing in intensity sometime around 12 pm to 3 pm. Up to 6″ of snowfall is expected during the daylight hours on Saturday. By Sunday morning we expect 12-18″ of snowfall. Coastal areas near Portage and Placer will likely receive higher snow totals. Snow line is expected to be around 500′ on Saturday.

Tomorrow: The heavy snowfall and strong winds will continue on Sunday. Winds are expected to peak overnight on Saturday and drop off slightly on Sunday with averages of 20-40 mph and gusts of 50+ mph. Another 12-18″ of snow is expected from Sunday morning through Monday morning, with snow line increasing to 1500′ on Sunday. Storm totals from Saturday through Monday are expected to be in the 2-3″ of water range, which is a lot of new load on the snowpack.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 0 0 40
Summit Lake (1400′) 21 0 0 27
Alyeska Mid (1700′)
Bear Valley – Portage (132′) 34 0 0

* Alyeska Mid stopped reporting at 9am on December 30th

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22 ENE 9 28
Seattle Ridge (2400′) 25 SE 5 18
Observations
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Riding Areas
Updated Fri, January 06th, 2023

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
Opened Dec 13th.
Placer River
Closed
Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Skookum Drainage
Closed
Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Turnagain Pass
Open
Opened Dec 13th.
Twentymile
Closed
Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Seward District
Carter Lake
Open
Opened Dec 13th.
Lost Lake Trail
Open
Opened Dec 13th.
Primrose Trail
Open
Opened Dec 13th.
Resurrection Pass Trail
Closed
Closed to motorized use for the 2022/23 winter season per Forest Plan. Open next season.
Snug Harbor
Open
Opened Dec 13th.
South Fork Snow River Corridor
Open
Opened Dec 13th.
Summit Lake
Open
Opened Dec 13th.

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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.