Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, November 29th, 2021 - 7:00AM
Expires
Tue, November 30th, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger has risen to CONSIDERABLE on all aspects above 1,000′. Strong east ridgetop winds with light snowfall have begun this morning and will be forming sensitive wind slabs on any slope that is seeing active wind loading. Wind slab avalanches could be up to 2 feet deep and may occur naturally while human triggered wind slabs will be likely. Additionally, on all slopes above 1,000′, slab avalanches breaking in buried weak layers around 2 feet deep could be triggered by a person or by a smaller wind slab that steps down.

The danger below 1,000′ remains MODERATE where an avalanche occurring above may run into this zone.

Special Announcements
  • A Winter Weather Advisory, issued by the National Weather Service, is in effect for Portage Valley and Whittier from 9am today through 9am tomorrow.
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Mon, November 29th, 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

No known avalanche activity from yesterday. There were several human triggered avalanches, most of them remotely triggered from the top/side, on Saturday. See them listed on Andrew’s forecast from yesterday HERE.

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

A low-pressure churning in the Gulf is sending clouds, light snowfall and wind our way. Around midnight, ridgetop winds turned easterly and have climbed to the 20’s mph already with forecasted winds today in the 20-30 mph range with gusts near 50mph. Snowfall is on the modest side, with 2-3″ expected for Turnagain, 3-5″ for Girdwood and only a trace in Summit lake (a bit more tomorrow). With a welcome warm up to a more reasonable 15-25F, snow is expected to fall to sea level as temperatures in general remain below freezing,

Wind slabs and cornices are likely building as we speak and may even be releasing naturally. With upwards of 2 feet of loose snow available for transport, even on ridgetops, it should not take long for this new avalanche problem to develop. Essentially, we have fresh wind slabs forming over the top of our persistent slab issue we’ve been dealing with. More on that below.

Things to keep in mind today:

  • Watch for, and avoid, slopes that are being actively loaded
    • New slabs are likely to be very touchy
    • They could step down to buried weak layers, creating a much larger avalanche
  • Pay attention to any cracking in the snow around you or collapsing (whumpfing)
  • Sticking to areas below treeline (below ~2,500′) and out of the wind will drastically reduce the chance for triggering an avalanche.

Snowfall totals expected over the next three days. We are fortunate to have such support from the Anchorage NWS Forecast Office!

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

As we’ve been harping on, those weak layers under last week’s new snow are still a concern. Whether it is a layer of buried surface hoar or facets, the main point is, weak layers of snow sit around 2′ below the surface. It was evident they were still reactive on Saturday in both Turnagain and Girdwood. Several remotely triggered slabs occurred on Seattle Ridge (both sides of the ridge) and one remote triggered slab on Max’s in Girdwood Valley. Luckily, no one was caught up in any of these.

With new wind slabs forming on top of these weak layers, it’s a likely case that a wind slab avalanche could step down and trigger a larger slab, as mentioned above. However, what about those areas out of the wind? We still need to keep our guard up and look for any signs the loose snow has enough cohesion to act like a slab. Both cracking and whumpfing, along with feeling the snow with your boot or ski pole, to see if there is any stiff snow hidden under the top foot or so will good ways to assess the slope you are on.

Three pockets (small slab avalanches) that were remotely triggered from either the ridge or, more likely, from a snowmachiner out of view to the looker’s right of the slabs. Seattle Ridge, Minus 1 Bowl (Warmup Bowl), 11.27.21.

 

Remotely triggered slab on the SE face of Seattle Ridge by riders playing in the lower angle terrain above and to the side. Photo: Andy Moderow, 11.27.21.

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glide avalanches have really slowed down (relatively…) in the past two weeks. The last known glide crack that released was on Lipps SW face, sometime in the past week. With so many glide cracks in the area, and the fact there is no way to know when they will release, limiting your time under these is just a good idea. They really would be a horrible thing to encounter, potentially unsurvivable.

Weather
Mon, November 29th, 2021

Yesterday:  Mostly sunny skies quickly turned gray and cloudy by the afternoon. Ridgetop winds were light (~5mph) from a westerly direction. It was markedly cold… most stations stayed below 0F the day.

Today:  Overnight, a weather system has begun to move in from the Gulf. Ridgetop winds swung easterly around midnight and bumped into the 15-20mph range with gusts in the 40’s at Sunburst. Light snowfall is starting and by tonight, 2-3″ looks to fall at Turnagain Pass and closer to 3-5″ in Girdwood. Temperatures are slowly climbing into the 10F range and should remain between 10-20F at all elevations.

Tomorrow:  Snowfall is forecast to continue though tomorrow and move out on Wednesday. Another 3-5″ for Turnagain and 4-8″ for Girdwood is the guess right now, with a bit more in Portage Valley. Ridgetop winds should decrease significantly down to 5-10mph or even calm for the latter part of the storm. Temperatures will rise to near 20-30F at sea level, but this will remain cold enough for snow.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 0 0 0 ~63*
Summit Lake (1400′) -8 0 0 ~10
Alyeska Mid (1700′) 0 N/A* N/A* N/A*

*Snow depth at Center Ridge and Summit Lake are estimated. Alyeska precipitation sensors are not yet operational for the season.

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -3 W 5 41 (E 3am)
Seattle Ridge (2400′) -1 VAR 2 18 (SE 4am)
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.