Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, December 21st, 2021 - 7:00AM
Expires
Wed, December 22nd, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE in areas being impacted by the strong northwest winds, predominantly above 2,500′. Just after midnight, ridgetop winds increased dramatically. Any new wind slab will likely be easy to trigger by us and may release naturally. Watch for signs of recent, or active, wind loading. Otherwise, on all slopes above 1,000′, there is a MODERATE avalanche danger where a person could still trigger a larger slab, 2 to 5+ feet deep, that breaks in old buried weak layers.

Below 1,000, the danger is LOW where triggering an avalanche is unlikely.

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Tue, December 21st, 2021
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
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 (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

Happy Winter Solstice, everyone! A quick shot of snowfall was over the region yesterday. Girdwood, Placer Valley, and Turnagain Pass all saw around 3-5″ of new snow, including to the south of Turnagain Pass. Although this is a nice refresh, maybe not so much above the trees as right around 2am this morning those pesky northwest winds really ramped up.

The Sunburst weather station, which doesn’t pick up this wind direction very well, saw a gust to 48mph. The AKRR Milepost 43 station, which does pick up these winds well, recorded a gust of 70mph at 4am. That said, average winds have been around 20mph, just right for moving snow. The wind should remain through the day and diminish somewhat before increasing again tonight.

Fresh wind slabs should be easy to find and trigger on those slopes that see recent or active wind loading. Natural winds slabs are possible as well in these windy locations. If you are headed out today, watch for those signs of wind loading, cracking in the snow around you and feel for stiffer snow over softer snow. These northwest winds have unusual loading patterns. They can funnel through Turnagain Pass in a way that produces a south wind on the east (non-moto) side of Turnagain Pass, which creates loading on the north side of the ridges. The winds can also split around Turnagain Pass, saving it from too much wind damage in general, but it’s too early to tell if this will be the case.

The good news is, we should be able to easily use our observation skills to suss out whether the winds have, or are, moving snow around in the area we choose to travel. If there is no wind effect, then we are dealing with that annoying persistent weak layer 2 to 5 feet down or any old wind slab that could be lingering from days ago.

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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

That’s right, we are still talking about those old faceted layers from early November that are buried anywhere from 2 to 5+ feet deep. It has been just about 10 days now since they were last producing avalanches. That was on the tail end of the last snowfall on Dec 9-10. Many of us have been digging down to these layers, especially where they are shallower (around 3 feet or less) and testing them. They are doing what a ‘deep persistent slab’ problem does, which is the facets are getting harder (good) and the layer takes more force to make it fail (also good). But, that doesn’t mean we are out of the woods.

There is still a chance someone could hit a thin spot and create a large avalanche. That likelihood is becoming less as the days go by, but still something we all should keep in mind, especially when venturing to new areas. Some areas, such as the Placer Valley in the video below, have a much larger slab while others, more on the south end of Turnagain Pass, have a much shallower slab. The shallower the snowpack, the thinner the slab, and the more likely it is we can cause the weak layers to fail and potentially cause an avalanche.

Snow pit at 2,050′ in the Summit Lake area that has a shallower snowpack, just to the south of the advisory area. A large whumpf was experienced at this location, evidence that the facets are able to collapse with the weight of a person(s). Photo: Andy Moderow, 12.19.21.

Weather
Tue, December 21st, 2021

Yesterday:  Cloudy skies, light snowfall and warm temperatures were over the region. Between 3-5″ of snowfall was seen in most areas, with snow to sea level. Ridgetop winds were light (5-10mph) from the west. Temperatures rose to the mid to upper 20’sF at all elevations (including the ridgetops) where they have remained.

Today:  Early this morning the NW winds picked up dramatically into the 25mph range with gusts near 50mph. This is in conjunction with clearing skies and cooling temperatures. Ridgetop winds are forecast to remain in the 20-25mph range through the day. Temperatures are on a slow decline back to the teens for this evening along with clear skies.

Tomorrow:  Partly cloudy skies, light NW winds and temperatures in the teens are on tap for tomorrow. Another bump in NW winds may shape up for tomorrow night into Thursday. It looks like it will be after Christmas till there is another shot for snow.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26 3 0.4 71
Summit Lake (1400′) 22 3 0.3 N/A
Alyeska Mid (1700′) 24 4 0.4 44

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 NW 10 48
Seattle Ridge (2400′) 22 NW 15 39
Observations
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Riding Areas
Updated Sat, November 26th, 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.