Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, March 17th, 2022 - 7:00AM
Expires
Fri, March 18th, 2022 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′. Wind slabs at upper elevations along ridgelines and cross loaded gullies are possible for a person to trigger. Storm slab avalanches in protected terrain are also possible in areas that receive higher snowfall totals such as Girdwood, Portage, or Placer. An older layer of buried surface hoar from 3/2 is a concern for larger avalanches that could release on lower angle slopes. Careful evaluation of the snow and terrain are recommended before entering avalanche terrain. Below 1000′ the avalanche danger is LOW.

Special Announcements
  • Come join us for the Turnagain Pass Avalanche Awareness Day on Saturday, March 19th in the Seattle Ridge parking lot. Chat with CNFAIC forecasters, try out some avalanche rescue gear, and demo a snowmachine or two from local businesses such as AMDS and Anchorage Yamaha and Polaris.
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Thu, March 17th, 2022
Alpine
Above 2,500'
Moderate (2)
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
Moderate (2)
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
  • 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

The storm impacting the area over the past 24 hours is following a familiar pattern, with underwhelming snowfall amounts in Turnagain Pass (2-4″), higher amounts in Girdwood (3-6″), and higher again in Portage and Placer (6-9″). Light to moderate snow is forecast to continue throughout the day today and should add another 1-2″ in Turnagain Pass and Girdwood and 3-6″ in Portage and Placer.  The winds have tapered off to 10-20 mph after strong gusts yesterday morning in the 30-50 mph range. Wind slabs at upper elevations are the primary avalanche problem today in areas that receive less than 9-12″ of storm snow. Wind slabs are possible for a person to trigger but unlikely for natural triggering now that the wind speeds have backed off. If you see active wind loading in the area you are travelling then natural avalanches are possible and you should be aware of overhead avalanche terrain.

In coastal areas that have received significantly higher snow totals and will continue to get new snow today there is the potential for storm slab avalanches in protected areas. A layer of surface hoar buried underneath the new snow could make those storm slabs easier to trigger and propagate more widely than typical. Keep an eye out for shooting cracks or collapsing (whumphs) and use test slopes to determine whether the new snow is bonding well to the old snow surface. On Tincan yesterday, the new snow was shearing off easily in hand pits on top of the upper layer of buried surface hoar but there was only about 4″ of new snow which was not enough to create storm slab conditions.

Glide Avalanches: Glide cracks have opened up across the forecast area including near the Seattle Ridge uptrack and on the south faces of Eddies and Tincan. With continued warm temperatures these cracks could potentially release, causing a very large and destructive avalanche. Minimize time spent underneath them to limit your exposure to this hazard.

Loose Avalanches: Both dry and wet loose avalanches are likely with the new snowfall. On southern aspects the combination of warm temperatures and sun was creating moist snow at the surface yesterday which could create wet loose avalanches on steeper terrain. On northern aspect dry loose avalanches are likely in the new snow on steeper terrain.

Small wind slabs naturally triggered by wind loading yesterday at 2300′ on the lower end of CFR on Tincan Common. Photo 3.16.22

Broken cloud cover interspersed with periods of obscured clouds and light snow in Turnagain Pass yesterday. Photo 3.16.22

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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

A layer of buried surface hoar and near surface facets from 3/2 have been responsible for several human triggered avalanches in the forecast area and could become more active again with a fresh load of new snow. It can be difficult to spot this layer in a snowpit and performing an instability test, like an extended column test or compression test, can help identify the layer and give you a sense of how reactive it is in the area you are travelling. On Tincan yesterday, we found the 3/2 buried surface hoar down 16-20″ from the surface and had no propagation in our instability tests on the layer with consistently hard results in terms of number of taps to initiate the layer (ECT N 23, 26). In my pit there was a notable collapse in the weak layer when it failed in the ECT, which is a common characteristic of buried surface hoar. The distribution of this layer is variable but it seems to be most prevalent in Turnagain Pass, both on the skiers side and along Seattle Ridge.

Snowpit structure from 2400′ on NW aspect of Tincan. Photo 3.16.22

Weather
Thu, March 17th, 2022

Yesterday: Warm temperatures and broken to obscured cloud cover. Intermittent light to moderate snow above 1000′ with rain below. Only 1″ of snow accumulation over the last 24 hours at Turnagain Pass, with Girdwood receiving about 2″ of snow and Portage/Placer area received up to 6+” of snow. Winds were light to moderate in the 10-15 mph range with gusts of 15-25 mph at ridgetops for most of the day. Yesterday morning some gusts were into the 35-50 mph range from 6am to 1pm.

Today: Conditions look largely similar to yesterday, with warm temperatures and snowfall expected throughout the day. Snow accumulation also looks similar to yesterday with 1-6″ of new snow today favoring Girdwood and Portage/Placer. Temperatures are forecast to decrease slightly this afternoon with snow line around 500′ today. Winds should average around 10-20 mph with gusts into the 30s.

Tomorrow: Another pulse of snowfall is expected to impact the area tomorrow, with 6-16″ of snow from Friday morning through Saturday Morning. Higher snowfall totals will favor coastal areas. Wind speeds should also ramp up as the next pulse of snow comes into the area tomorrow morning.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 35 1 0.1 91
Summit Lake (1400′) 35 0 0 39
Alyeska Mid (1700′) 33 2 0.2 NA

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) NA NA NA NA
Seattle Ridge (2400′) 25 SE 12 25
Observations
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Riding Areas
Updated Fri, May 13th, 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
Closed as of May 1 per Forest Plan.
Placer River
Closed
Closed as of April 25th due to insufficient snow coverage.
Skookum Drainage
Closed
Closed as of April 1st per Forest Plan.
Turnagain Pass
Open
Open. Extended opening through May 31.
Twentymile
Closed
Closed as of April 6th due to insufficient snow coverage.
Seward District
Carter Lake
Closed
Closed as of May 1 per Forest Plan.
Lost Lake Trail
Closed
Closed as of May 1 per Forest Plan.
Primrose Trail
Closed
Closed as of May 1 per Forest Plan.
Resurrection Pass Trail
Closed
Closed as of May 1 per Forest Plan.
Snug Harbor
Closed
Closed as of May 1 per Forest Plan.
South Fork Snow River Corridor
Closed
Closed as of May 1 per Forest Plan.
Summit Lake
Closed
Closed as of May 1 per Forest Plan.

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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.