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 7th, 2021 - 7:00AM
Expires
Wed, December 8th, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains HIGH due to a storm exiting currently and a round of strong wind from the northwest heading in. After 1-3′ of snowfall during the past 2 days and many natural avalanches (breaking into older weak layers), we can expect more natural avalanches today in areas with strong northwest winds. Even in areas out of the wind, human triggered large avalanches are likely. Slabs could be in the 3-6′ deep range and simply nothing to mess with. Hence, travel in avalanche terrain is NOT recommended again today as the snowpack continues to be pummeled. This includes flat terrain below steeper slopes.

*Roof Avalanches: We had several reports of roofs shedding their snow yesterday. Until the cold air returns, roof avalanches remain a concern. Pay attention to children and pets, and be mindful of where you park your vehicles.

PORTAGE/PLACER:  Large avalanches may occur again today as the 2-3′ of new is affected by the strong westerly winds.

SUMMIT LAKE: Around 12″ of new snow has fallen and is the first major loading event on the weak snowpack in this area. Natural avalanches are likely today due to the strong NW winds.

SNUG HARBOR/LOST LAKE/SEWARD: A very dangerous snowpack has set up in these areas as 2-3′ of new snow is likely sitting on old weak faceted snow. Strong NW winds are likely to create natural avalanches and human triggered avalanches are very likely.

Special Announcements
  • There will be intermittent traffic delays for avalanche hazard reduction today on the Seward Highway from mile post 88 to 83, south of Girdwood, from 10:00 am to 2:00pm. Motorists should expect delays of 45 minutes.
    *Updates will be posted on the 511 system at 511.alaska.gov.
  • There are 8 days left to apply for an avalanche education scholarship through the Friends of the Chugach Avalanche Center. Application deadline is December 15. Click HERE for details!
Thanks to our sponsors!
Tue, December 7th, 2021
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
High (4)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
High (4)
Below Treeline
Below 1,000'
Avalanche risk
High (4)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Many large natural avalanches occurred yesterday during the peak of the storm. Despite the poor visibility, one backcountry skier witnessed a ‘huge powder cloud’ across Turnagain Arm while he was driving around 4pm yesterday. This was off the peak on the west side of Seattle Creek drainage (west of Pyramid Pk). A group ice fishing on Carter Lake heard the rumble of a large avalanche, 45 seconds of rumbling, late Sunday night off Wrong Mountain in the central Kenai Mountains. There were other naturals evident from new debris piles, some of them quite large, in the bottom of slide paths that could be seen from roads.

Debris from a large natural avalanche that occurred yesterday along the Seward Highway. 12.6.21. 

Avalanche in motion in Portage Valley, across from the Visitor’s Center. This slide was triggered by artillery during avalanche hazard reduction work. 12.6.21.

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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

The warm storm system that moved in Sunday, peaked yesterday, and is moving out this morning as we speak. Right on its heels however, are strong northwest winds that will usher in not only cold air, but clearing skies. By early afternoon ridgetop winds are slated to be blowing 25-35mph with gusts into the 50’s. This wind direction is completely the opposite from the storm and will likely be transporting a fair amount of new snow into sensitive wind slabs. Areas seeing the strongest winds are expected to also see natural wind slab avalanches. These wind slabs could step down into buried weak layers, creating a much larger avalanche.

Storm total estimates at 2,500′ beginning Sunday:
Girdwood Valley:  15-20″ snow (1.7″ of water equivalent)
Portage Valley:  2-3′ snow (2.5″ of water equivalent)
Turnagain Pass:  14-18″ snow (1.5″ of water equivalent)
Summit Lake:  10-14′ snow (1″ of water equivalent)
Lost Lake/Snug Harbor:  2-3′ snow (2.5-3″ of water equivalent)

The most dangerous places for us to be are either those that saw the most snow and/or those that will see the strongest winds today; that will be the south end of Turnagain Pass, Summit Lake, Snug Harbor, Lost Lake, among others. It’s a day to really watch the winds, but also know the snowpack itself can’t be trusted. If you are in an area with little wind, you could still be walking into a trap with those buried weak layers discussed below.

Low visibility at Turnagain Pass yesterday. This is looking at the lower slopes of Seattle Ridge from the motorized parking lot. 12.6.21.

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

It is a glaring sign that the weak layers down in the snowpack are still quite reactive when a storm that only had a couple feet of snow with strong winds created such large avalanches. For backcountry traveling, this is a really big concern as the weak layers (facets and buried surface hoar) are now further down and any avalanche triggered could be very large and destructive. Furthermore, these weak layers have been propagating long distances, and people have been triggering avalanches remotely- from above, below, and to the side of steep slopes.

All that said, the heart of Turnagain Pass didn’t see the ‘feet’ of new snow other places did, but we still have to be on our guard. With no visibility yesterday, we have no information yet as to natural avalanche activity. With winds today being a bit of a wild card here (meaning the northwest direction can sometimes miss parts of Turnagain) we have to assume it is as dangerous as it was last week.

This will be a great day to simply avoid any avalanche terrain and play in the flats and on slopes 30 degrees or less with nothing steeper above you. If you are at Turnagain Pass and find little wind and only a foot of so of new snow, the danger is more toward CONSIDERABLE. Be sure to have a cautious mindset, as triggering an unsurvivable slab in buried weak layers is still a very real possibility.

Weather
Tue, December 7th, 2021

Yesterday:  Warm and stormy weather. Rain fell up to 300′ in elevation at times and heavy snowfall above, heaviest near Portage and Seward. Winds were strong from the east, 35-45mph with gusts to the 80’s. Warming temperatures accompanied the weather (mid 30’s at sea level, mid 20’sF along ridgelines).

Today:  The storm system will be headed out this morning, only to be followed closely by strong NW winds. Skies should begin to clear through the day with temperatures headed back down to the single digits by tonight. Ridgetop winds are swinging around to the NW now and slated to blow in the 25-35 mph range with stronger gusts by this afternoon.

Tomorrow:  Models show a break in weather for Wednesday with mostly clear skies and chilly temperatures. The NW winds are forecast to abate by early Wednesday morning. It appears another round of stormy weather is headed our way for Thursday and Friday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30 11 1.1 71
Summit Lake (1400′) 28 4 0.3 24
Alyeska Mid (1700′) 29 11* 1.13 47*

*Estimated snowfall and depth numbers.

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21 NE 40 82
Seattle Ridge (2400′) 24 SE 20* 35*

*Data through 7pm yesterday when wind sensor became rimed over.

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.