Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, January 16th, 2023 - 7:00AM
Expires
Tue, January 17th, 2023 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The danger is CONSIDERABLE above 2500′. Last night brought a few inches of new snow with strong easterly winds, which will make human-triggered wind slab avalanches likely today, and natural avalanches possible. These fresh wind slabs are loading a snowpack with multiple weak layers, one of which is 1-2′ deep, while the other is 3-6′ deep or deeper. The snowpack is challenging so it is important to keep your terrain simple today, sticking with low-angle slopes. The danger is MODERATE between 1000′ and 2500′, where slightly weaker winds will make human triggered avalanches a little less likely. The danger is LOW below 1000′.

Special Announcements

Forecaster Chat #2:  Join us at the Girdwood Brewing Co. from 5:30-7:00 p.m. on Thursday, Jan. 19! CNFAIC forecaster Andrew Schauer will open the night with an overview of the state of the snowpack, followed by a discussion on how safe terrain management changes depending on the type of avalanche problem at hand. More details here.

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Mon, January 16th, 2023
Alpine
Above 2,500'
Considerable (3)
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
Considerable (3)
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

We saw small avalanches on short but steep wind-loaded features yesterday on Eddie’s. These were 6-18″ deep and around 50′ wide, failing on the layer of surface hoar that was buried five days earlier. The size of the terrain kept the avalanches small enough that they wouldn’t have buried a person. More details here.

Small avalanche I triggered with a ski cut on a test slope. 6-18″ deep, 50′ wide. The slope was previously wind loaded and the avalanche failed on a layer of buried surface hoar. 01.15.2023

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

We are dealing with two very different problems right now. The first and more likely problem to encounter is fresh wind slabs around a foot deep that have formed in the past 12 hours with strong easterly winds. These would be reactive enough on their own, but are made worse by the fact that they are loading a layer of surface hoar that was buried last week and was still reactive yesterday (details here). The second problem is a deep weak layer that is capable of producing massive avalanches, which will have higher consequences but will be more difficult to trigger (see problem 2 below).

Winds have been blowing out of the east at 15-30 mph since just after sunset yesterday, and although they should back off slightly during the day today, the slabs that have just formed will still be reactive. The most reactive slabs will be found at higher elevations, but you should anticipate some pockets of unstable snow reaching down into the middle elevation bands as well. Keep an eye out for recently loaded terrain features near ridgelines, on convex rolls, and in cross-loaded gullies. Fresh wind slabs will feel a bit stiffer, and may give you warning signs like cracks shooting out from your snowmachine or ski tips. Take the time to step off the skin track or hop off your snowmachine to see how the surface feels. Avoid steep slopes with stiff, wind-loaded slabs of snow on the surface. Remember, these avalanches near the surface may be the most likely problem to encounter, but there is potential for bigger avalanches failing deeper in the snowpack. Read on to problem 2 for more.

Fresh wind slabs that formed in the past 24 hours will be loading slopes that were already reactive, producing avalanches yesterday. This makes human-triggered avalanches likely today. 01.15.2023

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Aspect/Elevation
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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

It was hard to decide which avalanche problem got the number one spot in today’s advisory. Should it be the shallow, but more likely wind slab? Or should it be the less likely deep slab– difficult to trigger, but capable of producing avalanches big enough to take out large sections of forest or destroy a house? However you organize the avalanche problems, there is no question that the current snowpack is dangerous, and the way to manage it is by cautious terrain use.

It has now been 9 days since the last known avalanche on the Thanksgiving crust/facet combo that is buried anywhere from 3-6′ deep on average, but it is still a concern. Over the past week, we’ve been finding the same structure in our snowpits that produced the last avalanches on this layer. The most likely places to trigger an avalanche on this layer will be on slopes with a thinner snowpack. This is true as you consider the forecast area in general (generally thinner snowpack from the southern half of Turnagain Pass down to Summit Lake), or across specific slopes (thin spots on previously scoured terrain features where rocks may or may not be visible). There is a lot of uncertainty with deep slab avalanches, and the only way to truly manage your risk exposure with a problem like this is by stepping back from steep terrain.

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Weather
Mon, January 16th, 2023

Yesterday: Skies were mostly cloudy with temperatures in the upper 20’s to mid 30’s F. Winds were blowing 10-20 mph out of the east for most of the day, picking up to 15-30 mph with gusts up to 45 mph since yesterday evening. We’ve gotten 1-6” snow overnight, favoring Girdwood over Turnagain Pass. The rain line has been dropping from around 800’ to 500’.

Today: A short but heavy shot of precipitation should bring another 1-3” snow this morning before it breaks up, with rain levels around 500’. Winds are expected to blow 10-25 mph with gusts of 20-35 mph out of the east. High temperatures should be in the mid 20’s to low 30’s F during the day, dropping slightly to the mid to upper 20’s tonight.

Tomorrow: Precipitation is expected to pick up slightly tonight, with 3-5” snow by tomorrow morning and rain line staying down around 300’. Winds are looking to increase with the next round of precip, blowing 15-25 mph gusting 30-40 mph tonight, before backing off during the day tomorrow. Skies will be mostly cloudy with some pockets of broken clouds in the morning. High temperatures should be in the mid 20’s to low 30’s F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32 1 0.1 n/a
Summit Lake (1400′) 28 0 0 31
Alyeska Mid (1700′) 32 6 0.4 56
Bear Valley – Portage (132′) 38 rain 0.76 n/a

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 ENE 17 45
Seattle Ridge (2400′) 27 SE 12 24
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.