Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, April 6th, 2022 - 7:00AM
Expires
Thu, April 7th, 2022 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE above 1,000′ on all aspects. Fresh wind slab avalanches, up to a foot in depth, will be possible to trigger on wind loaded slopes. This is due to sustained moderate southeasterly ridgetop winds that began yesterday evening. There also remains a chance a person could trigger a larger slab, up to 2 feet deep, that breaks on an older buried weak layer. Additionally, watch for rollerballs and wet sluffs if the sun breaks through this afternoon and warms the snow surface.

Special Announcements
  • Twentymile:  The Chugach National Forest has closed the Twentymile drainage to motorized use as of today, April 6th, due to insufficient snow coverage. The Avalanche Center posts the status of motorized use in the ‘Riding Areas’ tab just below this announcement.
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Wed, April 6th, 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

There were no known avalanches yesterday. The last known avalanche was a skier triggered slab that was reported near the Seattle Creek Headwall on Monday. This slab was around a foot deep and 100′ wide on an easterly aspect around 3,400′ in elevation. The slab failed on weak snow over a thin crust under the storm snow from April Fools’ Day. The skier was able to ski off the moving slab.

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

Another brief shot of moisture is over the region this morning. However, only a trace to a couple inches of snow is expected before skies are forecast to start breaking up midday. Apart from a little new snow, it will be the southeast ridgetop winds that are more exciting. These winds picked up into the 10-20mph range with gusts near 40mph overnight and should continue through most of the day. How much snow the winds are able to transport is the big question. There was roughly 2-4″ of new snow fell yesterday along with another inch or two today that is available along with any pre-existing snow that is soft enough to move. Sun crusts on southerly aspects may limit some wind transport but from what Andrew and Graham saw yesterday in the Placer Valley, there was ample soft snow.

For anyone getting out today, keeping an eye out for active wind loading, watching for smooth rounded pillows of freshly deposited snow, hollow feeling snow, and cracking in the snow around you will be key. Wind slabs should be easy to suss out and in the foot deep realm. Areas in the higher elevations could sport some slabs up to 2′ deep where winds are strongest along ridgelines. This wind direction is a bit more southerly than we normally see, so really looking for new slabs in places you might not expect will be important, including over rollovers in the mid elevations and cross-loaded gullies.

Sunshine:  If the sun comes out, we can expect to see some rollerballs and wet sluffs on southern aspects as the surface melts. This is similar to what we have been seeing in the afternoons over the past few days.

Cornices:  As always, keep giving cornices an extra wide berth. Not only are the winds adding to them today, but any sun that shines this time of year can really add to destabilizing them further.

 

Ridgetop southeasterly winds transporting snow above the northwest face of Comet Pk in the Placer Valley yesterday evening. Also seen is an older avalanche that was likely a natural from the April Fools’ storm last Friday. 4.5.22.

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

Underneath the easy-to-see surface instabilities are a few lurking layers we have to keep in mind. The most concerning layer is the one closest to the surface. It’s the April Fools’ interface that sits in the top 1-2 feet in the snowpack. This layer is composed of small buried surface hoar and near surface facets that sit on a thin crust. It has been hard to get the layer to react in many pits, but it does react at times. It was also the layer responsible for many avalanches last weekend, with the last known avalanche occurring on Monday; noted above on the Seattle Headwall. It isn’t out of the question for someone to trigger another avalanche on this layer and even a wind slab avalanche could step down to it. With sun crusts on southerly slopes, the northerly aspects are most suspect until the sun melts off those sun crusts making south slopes a concern as well.

Deep Persistent Slabs:  The other buried layers are much further down, 3-6′ deep in the snowpack, and are from March. They are also composed of a thin layer of small buried surface hoar and small facets. These layers also show they can fail in just the right place every once in a while. An avalanche releasing on one of them would be very large, but at the same time they are very unlikely to trigger due to the depth and that the weak layer is healing in many places. We will continue to watch them as a big load of snow and/or rapid warming could reactivate them.

 

Weather
Wed, April 6th, 2022

Yesterday:  A brief period of snowfall yesterday morning was quickly followed by clearing skies and some sunshine. Between 2-4″ accumulated in most areas. Ridgetop winds were easterly in the 10-20mph range. Temperatures were in the 30’sF at the lower elevations and near 20F along the ridgetops.

Today:  Another quick shot of snow showers is over the region this morning bringing a trace to 2″ of snowfall (rain/snow mix at sea level). Skies are forecast to break up through the day with the chance for some instability showers here and there into tonight. Ridgetop winds are slated to remain gusty from the southeast, in the 10-20mph range with gusts in the 30’s. Temperatures will likely rise to near 40F at sea level and into the upper 20’sF along ridgetops.

Tomorrow:  Mostly clearing skies are forecast for tomorrow, Thursday. Ridgetop winds are expected to decrease and swing northwesterly (5-10mph range). Temperatures should rise with daytime warming back to more springlike conditions, possibly hitting 45F at sea level and the low 30’sF along ridgelines.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30 2 N/A 118
Summit Lake (1400′) 29 4 N/A 42
Alyeska Mid (1700′) 32 4.5 0.2 N/A

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 E 15 37
Seattle Ridge (2400′) 23 SE 9 19
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Riding Areas
Updated Fri, May 13th, 2022

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
Closed as of May 1 per Forest Plan.
Placer River
Closed
Closed as of April 25th due to insufficient snow coverage.
Skookum Drainage
Closed
Closed as of April 1st per Forest Plan.
Turnagain Pass
Open
Open. Extended opening through May 31.
Twentymile
Closed
Closed as of April 6th due to insufficient snow coverage.
Seward District
Carter Lake
Closed
Closed as of May 1 per Forest Plan.
Lost Lake Trail
Closed
Closed as of May 1 per Forest Plan.
Primrose Trail
Closed
Closed as of May 1 per Forest Plan.
Resurrection Pass Trail
Closed
Closed as of May 1 per Forest Plan.
Snug Harbor
Closed
Closed as of May 1 per Forest Plan.
South Fork Snow River Corridor
Closed
Closed as of May 1 per Forest Plan.
Summit Lake
Closed
Closed as of May 1 per Forest Plan.

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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.