Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, February 20th, 2021 - 7:00AM
Expires
Sun, February 21st, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. Triggering a slab avalanche 1-2′ thick remains possible on slopes 35 degrees and steeper. These avalanches could be shallow new wind slabs from today, stiff wind slabs from yesterday’s strong winds, or much older wind slabs and softer slabs sitting on various buried weak layers at all elevations. In steep terrain harboring soft loose surface snow, watch your sluff and give cornices a wide berth along ridgelines.

SUMMIT LAKE/LOST LAKE/SNUG:  The central Kenai Mountains saw a significant northwest wind event yesterday. Triggering small to large wind slab avalanches will be possible in these areas as well.

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Sat, February 20th, 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

The northwest outflow winds did a number in many locations yesterday. Blowing snow and plumes were hard to miss for anyone out and about. Alex McLain in Seward was able to capture a natural avalanche in motion off the Resurrection Peaks behind the Lost Lake trail just north of Seward; note, this is outside of our forecast zone. The extent of other natural wind slab avalanches in the region is still being determined.

There were two human triggered avalanches yesterday. One was a snowmachine triggered wind slab on a small steep slope in Placer Valley. The other was a skier triggered persistent slab avalanche around a foot deep that failed on buried surface hoar in Placer Valley as well.


Natural avalanche and powder cloud behind the Lost Lake trail north of Seward. 2.19.21. Alex McLain.


Avalanche with powder cloud makes its way down the slope. 2.19.21. Alex McLain


 

Small wind slab, easily triggered by riders ascending this small steep slope. 2.19.21.

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

After the onslaught of northwest winds yesterday, winds have turned around and are blowing around 20 mph from the east this morning. These east winds are expected to quiet down by midday and though they may move a bit of snow around, any new wind slab is likely to be small and shallow. Snow surfaces around the region are quite variable; wind scoured, wind loaded, and even reports of slopes out of the wind harboring soft settled powder. That said, not only are the surface conditions variable, but the avalanche conditions as well. The avalanche danger will hinge on yesterday’s wind slabs, any possibility of new small wind slabs today, and lurking weak layers in the top 2′ of the snowpack.

If you are headed out, keep an eye out for any fresh shallow wind slabs that today’s winds might form. The wind is from a different direction than yesterday so soft snow may still be available to move around. Additionally, watch for harder wind slabs that were formed yesterday. These are worth avoiding as they may be sitting on weak snow, keeping them from bonding quickly. They also might simply just be stubborn and not quite healed yet. These slabs could be stiff enough to allow you onto them before realeasing. Any wind slab has the potential to step down to weaker layers buried in the top 2′ of the snowpack. More on that below.

Watching for the standard red flags will be key. Stiff snow over softer snow, cracks that shoot out in the snow around you, and whumpfing (collapsing) of the snowpack.

Loose snow avalanches (sluffs): If you are lucky enough to suss out a steep sustained slope with only loose surface snow, watch your sluff. These cold temperatures will continue to loosen surface snow and even eat away at the wind slabs out there.

Northwest winds blowing snow off of Byron and Carpathian Peaks yesterday. 2.19.21.

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

Triggering a slab avalanche breaking in a persistent weak layer of snow 1-2′ deep in the snowpack remains a concern. Unfortunately, a couple layers of buried surface hoar and facets sit in the top couple feet of the snowpack. Steep slopes with and without obvious wind effect are suspect. Not only are many older wind slabs sitting on these layers of weak snow, but areas with softer settled snow are as well. Add to that lower elevation terrain – under 2,000′. Between 1-2′ below the surface a layer of facets sits on a buried crust. This faceted layer produced an avalanche under Notch Mtn in Girdwood two days ago.

This is all creating a persistent slab avalanche problem. As we’ve been mentioning, it’s tricky because these layers are not reactive everywhere. Knowing what slopes could slide what ones are not likely to is tough to determine. Paying attention to any signs of instability and using good travel protocol are ways to help hedge your bets.

 

Weather
Sat, February 20th, 2021

Yesterday: Mostly clear skies were over the region with very cold temperatures (single to minus single digits at most elevations). Moderate to strong northwest winds impacted the area with averages between 10-30mph with stronger gusts.

Today: Partly to mostly cloudy skies are expected today. A low pressure is passing to the south sending clouds and a chance for a few flurries our way (no accumulation). This low is shifting winds easterly and pushing the arctic air back north. East ridgetop winds are forecast to average in the 10-20mph range while temperatures climb back into the teens at all elevations.

Tomorrow: A return to mostly clear skies and cold northerly winds (although calmer than Friday) is slated for Sunday into Monday. Ridgetop NW winds are forecast to average in the 10-20mph range. Temperatures should dip back to the single digits and possibly minus single digits.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 6 0 0 115
Summit Lake (1400′) 4 0 0 44
Alyeska Mid (1700′) 6 0 0 114

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -1 NW 10 31
Seattle Ridge (2400′) 1 NW 11 23
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Riding Areas
Updated Fri, February 12th, 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
Open
No parking in turnaround at end of the road near the outhouse.
Placer River
Open
Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Skookum Drainage
Open
This area will close to machines on April 1 as per CNF Forest Plan. Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Turnagain Pass
Open
Twentymile
Open
Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Seward District
Carter Lake
Open
Lost Lake Trail
Open
Primrose Trail
Open
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season.
Snug Harbor
Open
South Fork Snow River Corridor
Open
Summit Lake
Open

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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.