Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, February 19th, 2023 - 7:00AM
Expires
Mon, February 20th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE on all aspects above 1,000′. Triggering a lingering wind slab formed over the past two days will be possible in exposed areas as well as in the trees. These are likely to be around a foot deep. Natural loose snow avalanches are possible as the sun may be strong enough to initiate these on southerly steep aspects. Sluffs are also likely to be triggered by us. Additionally, there are some weak layers in the top few feet of the snowpack in specific areas that could produce a larger avalanche. Last, give cornices a wide berth. The danger is LOW below 1,000′.

*Strong northwest outflow winds are forecast to develop tomorrow, Monday. If this is the case, avalanche danger may increase despite the sunny weather.

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Sun, February 19th, 2023
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

A few shallow wind slabs were triggered yesterday in Girdwood Valley’s Notch area. These were reported to be fresh wind slabs on the windloaded sides of rollovers in the trees. Report HERE.

 

Fresh wind slab skier triggered in upper Girdwood Valley (Notch area) yesterday. Thank you to Kakiko Ramos-Leon for the photo. 2.18.23.

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

After a long stretch of unsettled weather and poor(ish) visibility, what looks to be a nice sunny Sunday is on tap. Several inches of low density snow fell yesterday, with what looks to be an average of 4-6″ in most places. The winds over the past couple days have been moderate to strong from the east and enough to form wind slabs in some areas. With this, plus sunshine today and a few questionable buried weak layers, there are a lot of avalanche issues we should be on the lookout for if headed out.

Wind Slabs:  Lingering wind slabs, similar to the photo above, may still be triggered today. Although these are likely getting more stubborn with time, there could be some that are still touchy if they happen to be sitting on one of the various layers of buried surface hoar that have sprouted up over last week. Watch for cracking in the snow around you and stiffer snow over softer snow. These are expected to be in the foot deep range and found in the usual places along ridgelines, on rollovers, and in cross-loaded gullies. They could be a bit concealed by a skiff of new snow that fell after the winds.

SUN EFFECT:  The sun could be strong enough today to warm and initiate sluffs in southerly steep rocky terrain. These could start small, but with several inches of loose snow on the surface they could run further and gain more volume than one may expect.

Loose snow avalanches:  Watch your sluff. Just like that stated above, sluffs could be larger than expected and likely easy to trigger on steep slopes.

Cornices:  With weather conducive to ridgeline travel, be sure to give cornices a wide berth.

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

Although we have seen many areas with a generally stable snowpack, especially around Turnagain, there are still some questionable layers in the top 3 feet. A skier found one of these layers reactive in the Girdwood Valley (Crow Creek, Goat Shoulder) two days ago. At elevations between 1,000 and 2,000′ roughly a buried crust from Jan 25 exists that in places has weak facets above it. It seems that the thinner snowpack areas, where this layer is ~2′ deep or less, still has spots it is reactive. These areas are Crow Ck drainage and the southern end of Turnagain Pass toward Johnson Pass.

Additionally, over the past 10 days three layers of surface hoar grew in brief spells of clear skies that are now intermixed in the top foot(ish) of low density snow. These layers don’t seem to be causing much problem now, but the last known layer that formed on Feb 15, which sits around 6-10″ deep, seems like it could be more of an issue. Something to keep in mind moving forward. Quick hand pits to see if there are any easy shears, watching for cracking in the snow around us, and jumping on small test slopes, will be tools for sussing out any funny business under the soft surface snow.

 

This is a photo of an Extended Column Test (ECT) that broke in an old layer of buried surface hoar but did not propagate. It’s a good sign when these tests do not propagate. Thanks to Blase Reardon (Director of the Flathead Avalanche Center in Montana) for the photo and test results. 2.18.23.

 

Avalanche legend Nancy Pfeiffer came out to look at the avalanche that was skier triggered on Friday up Crow Creek. We found the slab (14-16″ deep) to have released on facets over the 1/25 crust. 2.18.23.

Additional Concern
  • Deep Persistent Slabs
    Deep Persistent Slabs
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.
More info at Avalanche.org

In areas with a thin snowpack (i.e, Silvertip and the southern end of the forecast region to Summit Lake) there are various weak layers near the base of the snowpack that remain a concern. For these areas, triggering a larger avalanche is not totally out of the question and a more cautious mindset is recommended.

Weather
Sun, February 19th, 2023

Yesterday:  Overcast skies, light to moderate snowfall, and gusty winds were over the region yesterday. Between 2-6″ of new snow fell with the higher amounts in Girdwood/Portage/Placer valleys and Turnagain Pass. Ridgetop winds were 10-20mph from the east with gusts in the 30’s. Temperature were mild, near 30F at the lower elevations and in the low 20’s along ridgelines.

Today:  Mostly sunny skies with some valley fog is forecast today. Ridgetop winds turned northwesterly last night as the weather system moved out and they should blow in the 5-10mph range today with some stronger gusts possible. Temperatures are slowly cooling as the winds bring in colder arctic air (mid 20’sF at sea level and teens along ridgelines).

Tomorrow:  Another sunny day is on tap for tomorrow, and Tuesday, as ridge of high pressure builds over Southcentral. Unfortunately, the northwest ‘outflow’ winds look to pick on Monday into the 25-35mph range with stronger gusts. Temperatures will continue to cool with the northerly flow of cold air.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 3 0.2 69
Summit Lake (1400′) 27 1 0.1 37
Alyeska Mid (1700′) 27 4 0.2 74
Bear Valley – Portage (132′) 33 3 0.4

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 NE 11 39
Seattle Ridge (2400′) 23 SE 8 25
Observations
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Date Region Location
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Riding Areas
Updated Fri, February 10th, 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
Open
Closed Jan 5th due to lack of snow and reopened Feb 11th.
Skookum Drainage
Open
Closed Jan 5th due to lack of snow and reopened Feb 11th.
Turnagain Pass
Open
Opened Dec 13th.
Twentymile
Open
Closed Jan 5th due to lack of snow and reopened Feb 11th.
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.