Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, November 27th, 2022 - 7:00AM
Expires
Mon, November 28th, 2022 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at elevations above 1,000′. Triggering a wind slab avalanche formed by the recent NW outflow winds will be possible. These wind slabs are in the 1-2′ deep range and could be found in unusual places on exposed slopes and gullies. Additionally, at elevations above 3,000′, weak snow at the base of the snowpack is still on our radar and could create a much larger avalanche in high Alpine. The danger is LOW below 1,000′.

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Sun, November 27th, 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)
Recent Avalanches

The peak of the NW outflow wind event occurred yesterday and although significant wind transport was seen in many areas, there were only a handful of small wind slab avalanches observed. All of these occurred in the upper elevations (no photos). That said, there were likely more that went unnoticed and/or were blown in quickly with the winds.

Wind transport off Tincan Proper yesterday seen from Eddies Ridge. Note the direction, southerly winds loading northerly aspects along Tincan. This is an example of terrain channeled winds as the main wind direction was almost 180 degrees different – from the northwest. 11.26.22 Andy Moderow. 

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Aspect/Elevation
  • 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.

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

Triggering a wind slab avalanche will again be the main avalanche issue for today. Although the NW winds are slowing down currently, they could still be strong enough in some areas to continue transporting snow. Today’s ridgetop forecast is for 10-20mph NW winds gusting near 30mph. Either way, much of the terrain above the trees has seen a good degree of wind effect. Wind slabs are likely up to a foot thick at the mid elevations and could be in the 2′ range up higher.

For those headed out hunting for soft snow, watching the surface texture and signs of wind loading will be key. Winds are likely to have loaded unusual aspects due to terrain channeling, an example seen in the photo above. Along with looking out for smooth rounded pillow features, be sure to feel for stiffer snow over softer snow and watch for cracks that shoot out from you. How touchy these wind slabs are has yet to really be determined. They may be stubborn enough to allow a person onto them before releasing. Additionally, there is a layer of surface hoar from last week that was buried 4-6″ on Thanksgiving night that could keep slabs from bonding, or maybe not. These are questions we’ll be trying to answer the next few days and something for all of us to keep in mind. Quick hand pits are another tool to use to see how easy a wind slab wants to pop out.

 

Small pocket of a wind slab that Andrew triggered yesterday on a test slope at Eddies. A good example of what might be found today at the mid elevations and above. 11.26.22.

 

Another photo from Eddies yesterday of a skin track that was not only blown in, but loaded with a pillow of snow. Photo by Andy Moderow, 11.26.22.

Avalanche Problem 2
  • 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

At the high elevations, above 3,000′, we continue to track the weak October snow that sits right at the base of the snowpack. How likely this layer is to produce an avalanche is the main question for anyone headed to the higher peaks during this clear sky period. As we gather more information, we’ll be looking to see if the winds were able to overload it anywhere and create an avalanche breaking near the ground. We can’t rule this layer out as it has shown to react in some pit tests recently and facets are notoriously tricky. What we can do is remember it is there, take routes with minimal exposure, dig a pit and look for it, feel for any whumpfing, and simply be suspect, it is early season after all and there are a lot of unknowns.

Weather
Sun, November 27th, 2022

Yesterday:  Clear skies and strong NW outflow winds covered the region yesterday. The NW winds blew in the 20-30 mph range with the strongest gust recorded being 78mph at the AKRR Milepost 43 ridgetop station above Grandview. Temperatures were chilly with ridgetops near 10F and valley bottoms in the teens to 20’sF.

Today:  Another clear, breezy, and cold day is on tap. The NW winds are forecast to slow somewhat and average between 10-20mph with gusts near 30. Temperatures are dipping into the single digits along ridgelines this morning while valley bottoms are in the teens where they should remain through the day.

Tomorrow:  Cold and clear conditions are expected for the next serval days. The good news is the models are showing the winds backing off to light northerly, even along the high elevations, for the next few days.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 20 0 0 26
Summit Lake (1400′) 21 0 0 14
Alyeska Mid (1700′) 20 0 0 21
Bear Valley – Portage (132′) 28 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 8 NW 8 38
Seattle Ridge (2400′) 17 NW 15 29
Observations
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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.