Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, December 12th, 2022 - 7:00AM
Expires
Tue, December 13th, 2022 - 7:00AM
Forecaster
Andrew Schauer
High Avalanche Danger
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

The avalanche danger remains HIGH above 1000′. We have received 1-2′ snow overnight, and strong winds will continue through the day. Large to very large natural avalanches are likely as the winds continue to blow today, and human-triggered avalanches are very likely. Travel in avalanche terrain is not recommended. 

The danger is CONSIDERABLE below 1000′, and it is likely a person will be able to trigger a large avalanche in the new snow, with natural avalanches possible. Be aware of the potential for large avalanches running into low elevation runout zones.

SUMMIT LAKE: The Summit Lake area got around a foot of snow, with strong winds. This snow will overload a weak snowpack, making very avalanche conditions with large avalanches likely.

Special Announcements

Chugach State Park: This is the second major storm in less than a week. This storm is overloading a weak snowpack in the areas outside of our forecast area, making for very dangerous conditions region-wide.

Hatcher Pass Avalanche Center:  HIGH danger for Hatcher Pass as well – see today’s update at hpavalanche.org.

Motorized Areas: The Chugach National Forest is currently assessing motorized closures. Some zones are likely to open following this storm. Check the Riding Areas tab below for the latest info.

Forecaster Chat #1: Come join forecaster John Sykes at Alaska Mountaineering and Hiking from 7-8 pm on December 15th to discuss current conditions, how to submit quick and quality observations, and decision-making during complex snowpack conditions. Admission is free and all are welcome!

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Mon, December 12th, 2022
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
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
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Skiers reported small natural avalanches on Eddie’s and Tincan as the storm started to ramp up yesterday afternoon. With peak intensity overnight, it is likely there have been larger avalanches since then.

This natural storm slab avalanche buried the Tincan skin track yesterday afternoon. Photo: Collin Atkinson. 12.11.2022

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Aspect/Elevation
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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.

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

Avalanche conditions will remain very dangerous today. We’ve gotten 1-2′ snow in the middle elevations over the past 24 hours, equaling 1.5-2″ snow water equivalent (SWE). At upper elevations storm totals may be approaching 2.5-3′ snow. Along with the heavy snowfall, very strong easterly winds were blowing 30-60 mph with gusts up to 90 mph at the Sunburst weather station last night. The snowfall is tapering off this morning, but strong northwest winds are expected to blow 15-30 mph through the day. This is the biggest loading event so far this season, and it will make large to very large natural avalanches likely, with human-triggered avalanches very likely. With the combination of heavy snowfall and strong winds, we could see avalanches failing 3-5′ deep in the new snow alone– and this doesn’t include the deeper weak layers that may be pushed to their breaking point by this heavy load (see additional concerns for more).

Travel advice for days like this is simple: very dangerous conditions exist, so travel in avalanche terrain is not recommended. This includes traveling on steep slopes or spending any time below avalanche paths. Keep in mind that larger avalanches failing in upper elevation start zones have the potential to run long distances into lower runout zones. If you are trying to get out to enjoy the fresh snow, keep your slope angles very low (below 30 degrees), and be aware of what is above you.

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Additional Concern
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

As mentioned above, this is the biggest loading event we’ve seen this season. There are multiple weak layers buried anywhere from 2-6′ deep that may or may not be reactive today. One layer we are tracking is the Thanksgiving crust, which has developed facets above and below. It has not seen any major loading event until now. The other, and less likely, problem is the October facet layer right at the ground. We have been thinking this layer is no longer a concern, but with 1.5-2″ water weight added since yesterday afternoon, we might see otherwise. Given the potential for very large avalanches with the new snow alone, these layers are of secondary concern, but just another reason to give steep terrain a wide berth today.

This snowpit from Eddie’s yesterday shows the Thanksgiving crust/facet combo, which may produce avalanches today. Photo: Andy Moderow. 12.12.2022

Weather
Mon, December 12th, 2022

Yesterday: Snowfall picked up during the day, with peak intensity overnight. As of this morning weather stations are showing 1.5-2″ SWE, which is equal to around 1-2′ snow. Strong easterly winds were blowing 30-60 mph with gusts to 90 mph along the ridgetops overnight. Temperatures have slowly increased from the mid teens to upper 20’s F since yesterday morning. The rain line has stayed down at sea level for this storm.

Today: We may see another inch or two of snow before the storm passes this morning. The northwest wind will be the big story for today, with sustained speeds of 15-30 mph and gusts of 40-50 expected today. These winds usually hit Summit Lake and Crow Pass harder than Turnagain Pass, but all of these zones should see significant wind loading today. High temperatures are expected in the low to upper 20’s F, with lows dropping into the single digits F starting this afternoon. Skies are overcast this morning, but clouds are expected to break up during the day with partly cloudy skies by this afternoon.

Tomorrow: There is a chance of 1-3″ snow tomorrow for our advisory area, as another system approaches that looks to favor Anchorage and Hatcher Pass. Skies will be overcast with easterly winds blowing 15-25 mph out of the east-southeast. The snowline is expected to stay near sea level. We are looking at another strong system Wednesday night into Thursday, so be sure to stay tuned to see how it develops.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26 17 1.5 47
Summit Lake (1400′) 25 11 1.0 33
Alyeska Mid (1700′) 25 20 1.8 44
Bear Valley (132′) 32 17 1.7

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 17 ENE 30 90
Seattle Ridge (2400′) 21 SE 15 37
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.