Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, December 18th, 2022 - 7:00AM
Expires
Mon, December 19th, 2022 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is at the high end of the MODERATE scale at elevations above 1,000′. Triggering an unmanageable avalanche 1.5-3 feet deep that breaks in buried weak layers is possible. These could be triggered from the side or bottom of a slope, or after several people have been on the slope. It’s a tricky situation and sticking to safe travel practices and a conservative mindset will be key. At all elevations, sluffs in the loose surface snow should be expected in steep terrain.

PLACER VALLEY/LYNX CREEK/JOHNSON PASS:  We have little information for these areas and triggering an avalanche could be easier to do. A very cautious mindset is recommended if heading to less traveled zones.

SUMMIT LAKE:  The snowpack is very weak as a whole in the Summit Lake area. Extra caution is warranted here as well where triggering an older wind slab or larger slab could occur.

Special Announcements

Chugach State Park: Many reports have come in describing unstable snow in the Anchorage Front Range. An avalanche in North Bowl (near the South Fork of Eagle River) occurred yesterday afternoon, no one is believed to have been caught.

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Sun, December 18th, 2022
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
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
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

We did not hear of any avalanche activity in our forecast zone yesterday. The last known avalanches were from early Thursday morning after the last snowfall/wind. Pictured below are some of the larger slabs that likely released around this time on Lipps and Pete’s North, photographed yesterday.

 

Large slab on the west face of Lipps ridge that appears to have broke in weak snow near the Thanksgiving crust. Andy Moderow 12.17.22. 

 

Several avalanches on the SW face of Pete’s North. One has especially wide propagation, indicative of an avalanche breaking in a buried weak layer rather than just a storm slab avalanche. Andy Moderow, 12.17.22.

Avalanche Problem 1
  • 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

Thank you for all the report-outs from people in the mountains yesterday! We heard of a few large ‘whumpfs’, but no avalanches. We also heard of folks that didn’t see any signs of instability. It is becoming clear however, that the weak faceted snow above and below the crust formed just before Thanksgiving is concerning in many areas; mostly in shallower areas such as the south end of Turnagain Pass, Lynx Ck, and Silvertip. Also, the Girdwood Valley has proven to be a problem spot as well. That said, with a few more clear sky days and easy travel, we still need to approach the slopes with extra caution. We are in one of those ‘scary’ MODERATE phases.

Hence, triggering a slab avalanche that breaks 1.5-3 feet deep is possible. This kind of avalanche could be triggered remotely, meaning from the bottom, sides, or on top of a slope. It could also release after several people have been on the slope. There may be NO signs of instability before an avalanche is triggered. This can set us up to think all may be fine until it is not. Good ways to manage this are to take extra care to travel one at a time in avalanche terrain, whether you are ascending or descending. Consider travel routes to limit exposure, always have escape routes planned, and watch your partners. Choosing lower angle slopes, 30 deg or less, can be a good way to just avoid the problem for those of us with lower risk thresholds. That said, if you hear a ‘whumpf’ that’s a problem and re-evaluating your plan, as several groups have done in the past few days, is prudent.

 

Weak faceted snow found above and below the Thanksgiving crust. This was around 2,300′ on a NE aspect in the Notch area of Girdwood Valley. The slab was around 2.5′ thick and composed of all the December storm snow. Ethan Tyler, 12.17.22.

Weather
Sun, December 18th, 2022

Yesterday:  Cold and clear! Minus single digits in valley bottoms and teens to even 20F along the ridgelines due to an inversion in place. Ridgetop winds were light from the east to SE.

Today:  Clear skies and cold temperatures will remain today. However, the inversion has weakened slightly with ridgelines remaining in the teens. Winds along the ridgetops should be calm to light from a northerly direction.

Tomorrow:  Partly sunny skies, cold temperatures, and light easterly winds are expected through Tuesday. Clouds move in along with a chance for a few flurries on Wednesday. The next shot for decent snow amounts looks to be Friday into next weekend.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 18 0 0 39
Summit Lake (1400′) -2 0 0 29
Alyeska Mid (1700′) 17 0 0 42
Bear Valley (132′) -5 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 E 4 22
Seattle Ridge (2400′) 21 SE 4 10
Observations
Recent Observations for Turnagain Pass
Date Region Location
02/08/23 Turnagain Observation: Eddie’s
02/07/23 Turnagain Observation: Seattle Ridge
02/07/23 Turnagain Avalanche: Pete’s North
02/06/23 Other Regions Observation: Johnson Pass to Bench Lake
02/05/23 Turnagain Observation: Rookie Hill
01/31/23 Turnagain Observation: Johnson Pass area
01/29/23 Turnagain Observation: Tincan Backdoor
01/28/23 Turnagain Observation: Sunburst
01/28/23 Turnagain Avalanche: Seattle Ridge
01/28/23 Turnagain Observation: Tincan Common
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.