Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, February 22nd, 2021 - 7:00AM
Expires
Tue, February 23rd, 2021 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE today. With increasing northwest winds it will be possible to trigger shallow fresh wind slabs in wind-loaded terrain. In addition there are buried weak layers, 1-2′ deep in the snowpack, that may still be triggered on steep slopes. Watch for blowing snow and changing conditions. Assess the snowpack as you travel, identify areas of concern and evaluate terrain consequences.

SUMMIT LAKE/SNUG/LOST LAKE/SEWARD:  The winds are forecasted to be stronger in the central and southern Kenai Mountains. There is the potential for natural wind slab avalanches in these areas again. Extra caution is advised.

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Mon, February 22nd, 2021
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 received social media report of a skier triggered slab avalanche yesterday in the forecast area described as a “decent scare”. We hope to get a bit more information today, including the specific location.

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

West to northwest winds are forecast to be elevated in the afternoon today, 10-20 mph with gusts into the 30s. They aren’t expected to be quite as strong as last Friday but watch for blowing snow again. There is still snow available for transport including the fluff that fell Saturday. With this there will be the potential for newly formed small wind slabs. As Wendy mentioned for Friday, this wind flow direction is tricky for Turnagain Pass. It can funnel through the Pass from the south and load north aspects on the non-motorized side, while at the same time load the SE face of Seattle Ridge. It can also split around the Pass and not affect much of the terrain in the heart of Turnagain at all. You might find you are in an area that is seeing no wind, or not enough to move the surface snow into wind slabs. This wind pattern also increases through channeled terrain and can be more pronounced in Crow Pass and Portage. Pay attention to blowing snow and active wind-loading.  There may also be old lingering wind slabs from the past wind-loading. Look for smooth pillowed snow on convexities, cross-loading in gullies and feel for stiff snow over softer snow. As always, watch for signs of instability like shooting cracks from your skis or machine.

If you do find and trigger a new wind slab, remember it could step down to old buried weak layers deeper in the snowpack. In this case, a larger avalanche is possible (more on this in Problem 2).

Sluffs: It will be easy to trigger loose snow avalanches (sluffs) in steep terrain that has been sheltered from the winds. It is unlikely an avalanche like this would be big enough to bury a person, but they can have serious consequences if they carry you into terrain traps like cliffs, rocks, or trees.

Forecast elevated winds today looking at the NAM on Windy. Watch for blowing snow!

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

As mentioned above, it is still possible to trigger an avalanche on two different persistent weak layers in the upper 2’ of the snowpack. One is a layer of surface hoar that was buried on 1/28, and the other is a combination of near-surface facets and surface hoar that was buried on 2/9. Both of these layers are slowly becoming more stubborn to trigger, but they are still showing that they are capable of producing avalanches. There were human-triggered avalanches on these layers last Thursday and Friday and observers have been still been reporting whumpfing. We suspect that the skier triggered avalanche that occurred yesterday may have involved one of these layers as well.  The layers of weak snow have been found across the forecast area in all elevations bands. However, lower elevation (below 2000′) steep terrain, where there is a crust combined with the weak snow, seems to harbor the most reactive set-up.

In addition, these weak layers may be sitting under old wind slabs and hard to identify.  They are also potentially getting another layer of wind-loaded snow on top today. Triggering a fresh wind slab may step down to a buried weak layer. Overall the snowpack has to be viewed with some uncertainty and caution.  If choosing to push into steeper terrain, keep in mind that these weak layers exist, watch for signs of instability (with the caveat that they may not be present but the slope may be unstable), follow safe travel protocol and evaluate terrain consequences. Imagine an avalanche, 1-2′ deep, propagating across the terrain. If the slope does avalanche where will you end up?

Both buried weak layers visible in a snow pit wall on Sunburst, 2.17.21.

 

 

Weather
Mon, February 22nd, 2021

Yesterday: Skies were partly cloudy to mostly sunny with temperatures in the teens and single digits F. Winds were light and westerly. Overnight skies were partly cloudy. Temperatures remained in the teens and single digits F and winds stayed light and westerly.

Today: Skies will be partly cloudy becoming mostly sunny.  Temperatures stay in the teens and single digits F. Winds will be from the northwest 10-20 mph with gusts into the 30s. Overnight skies will be mostly clear to start and then clouds increase in the early morning Tuesday. Temperatures will be in single digits but will slowly rise as clouds move in. Northwest winds continue 10-20 mph becoming light and variable after midnight.

Tomorrow: Mostly cloudy skies with afternoon snow showers. Winds will be light and variable becoming southeast 5-10 mph in the afternoon. Temperatures will be in the 20°Fs. Snow and easterly winds continue into Wednesday. I like this quote from the NWS this morning, If you want some more snow and a more active weather pattern, stay tuned to the forecast for this week. #snowtosealevelplease


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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 14 0 0 114
Summit Lake (1400′) 12 0 0 43
Alyeska Mid (1700′) 13 0 0 111

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 6 W 5 23
Seattle Ridge (2400′) 12 W 1 9
Observations
Recent Observations for Turnagain Pass
Date Region Location
05/18/21 Turnagain Observation: Tincan Ridge
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04/25/21 Turnagain Observation: Sunburst
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04/23/21 Turnagain Avalanche: Lynx Ck Drainage
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04/23/21 Turnagain Observation: Center Ridge Turnagain pass
Riding Areas
Updated Tue, June 01st, 2021

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
Placer River
Closed
It is packrafting and jetboat season!
Skookum Drainage
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
Turnagain Pass
Closed
Closed as of June 1. 188 day season, that\'s a wrap!
Twentymile
Closed
It is packrafting and jetboat season!
Seward District
Carter Lake
Closed
Closes May 1.
Lost Lake Trail
Closed
Closes May 1.
Primrose Trail
Closed
Closes May 1.
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season. Will be open for moto use in the 21/22\\\' winter season as per the CNF Forest plan.
Snug Harbor
Closed
Closes May 16th.
South Fork Snow River Corridor
Closed
Closes May 1.
Summit Lake
Closed
Closes May 1.

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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.