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 27th, 2021 - 7:00AM
Expires
Sun, February 28th, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE at all elevations. New and older wind slab avalanches will be possible to trigger today. New wind slabs, formed by a few inches of new snow and wind last night, are likely to be shallow (6-8″). Older wind slabs could be larger, around a foot thick, and hiding under the new snow. Additionally, a larger avalanche breaking in weak layers buried 1-3′ deep remains a concern at all elevations, including those below 1,000′.

*Roof Avalanches: Warming temperatures at sea level could cause roofs to shed their snow. Pay special attention to children, pets and where you park your car.

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Sat, February 27th, 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 had a report of a couple avalanches in the lower elevations north of the Girdwood Valley yesterday (1100-1900′). These were around a foot deep, 40′ wide and broke in older weak faceted snow. They were not large due to the smaller terrain features they occurred on. No one caught.

We also had a report of a group in the Eddies and Sharks Fin area (north side of Turnagain Pass) who experienced three ‘massive whumpfs’ at the lower elevations (800-1300′). No avalanches triggered.

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

Much anticipation surrounded last night’s snowfall event and hopes remain for the next system slated for this evening. Unfortunately, there just wasn’t quite enough oomph… It appears only 2-4″ of snow fell overnight, yet there is a small chance another inch or two more could fall before a break in precipitation midday. The next system moves in this evening with a shot for 2-3″ of additional snow tonight. Winds associated with last night’s event were steady in the 15-20mph range from the east and have decreased this morning. Expect the east winds to slowly rise through the day and by sunset be blowing around 20mph.

Wind Slabs:  Avalanche issues will be centered around new wind slabs formed in the new snow. These should be relatively shallow, in the 6-8″ range due to the modest new snow amounts. However, there are some older wind slabs under the new snow that still could be triggered. In this case, a larger slab may release. Furthermore, that funny business of facets and buried surface hoar sitting in the top few feet of the pack could also create a larger avalanche (more on that below in Problem #2).

Things to watch for today:

  • New fresh wind slabs from last night (should be easy to identify)
    • Look for recent wind deposited snow, stiff snow over softer snow
    • Watch for cracks that shoot out from you
    • If the winds pick up earlier than expected today, watch for active wind loading and new wind slab formation
  • Lingering wind slabs are also a concern. Several of these were triggered the past couple days and may still be reactive.
    • Old slabs may be hidden under the new snow and difficult to identify
    • Quick hand pits are a good way to see if there is an older slab under a couple inches of fluff.

Storm Slabs?:  If you are lucky and find yourself in a zone with over 5″ of new snow, watch for shallow storm slabs. The new snow came in ‘upside down’, with heaver snow over lighter snow. This can allow for the new snow to avalanche as a soft slab with the slab thickness equal to the new snow depth.

Loose Snow Avalanches (Sluffs):  Shallow sluffs in the new snow will be likely today. Watch your sluff on the steeper slopes.

Wet snow sluffs?:  Temperatures warming to above freezing at sea level may create some roller balls and small wet sluffs on steep terrain features below 500′.

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

We continue to track two weak layers of snow (surface hoar and facets) buried in the top three feet of the snowpack. The data continues to show triggering an avalanche in one of these layers remains possible. The smaller avalanches from yesterday failed in one of these layers as well as the whumpfing reported.

We know these layers are present in most areas and at all the elevation bands. The trick is, they are not reactive everywhere. The new snow and wind-loading could add a little more stress to the snowpack. There may be old hard wind slabs sitting on top of the weak layers allowing you to get well out onto the slope before it fails or failing after other machines or skiers have have already ridden the slope. Triggering a fresh wind slab or cornice fall may step down to one of these buried weak layers. As we have said before, this snowpack has to be viewed with some uncertainty and caution.  We need to 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.

Snow pit at 3,600′ in the Johnson Pass area on the south end of Turnagain Pass (pit is from Thursday 2/25). Take home is there are facets in top couple feet of the pack here that are showing reactivity and hence the chance a person could trigger an avalanche 1-2′ deep at this location.

Weather
Sat, February 27th, 2021

Yesterday:  Cloudy skies were over the region yesterday. Light snow started to fall in the early evening hours as the first of two weather systems headed in. Snow accumulations as of the this morning are.         Ridgetop winds were east/southeasterly averaging 15-20mph with stronger gusts. Temperatures were mild, near 30F at sea level and the 20’s to teens in the mid and higher elevations.

Today:  Mostly cloudy skies with a chance for 1-2″ of snow in areas this morning before a quick break in precipitation is expected midday. This evening the next system rolls in, hopefully giving us 1-3″ of additional snow. Warming temperatures will keep snow heavier and more dense than last night. The rain/snow line will hover between sea level and 100′. Temperatures at sea level should be in the mid 30’sF while the mid and upper elevations sit in the 20’sF. Ridgetop winds are slated to average 10-20mph with stronger gusts from the east today, and pick up to 20-30mph overnight.

Tomorrow:  The weak storm systems push out early tomorrow morning and clearing skies are expected for Sunday. Unfortunately, the winds will swing back to the NW and are setting up to blow ~30mph along ridgetops during the day Sunday. Temperatures will drop with cold air being ushered in, we could be back to single digits by Sunday night. Stay tuned.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 27 1-3 0.1-o.3 114
Summit Lake (1400′) 28 1 0.1 44
Alyeska Mid (1700′) 27 3 0.2 117

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 E 14* 33
Seattle Ridge (2400′) 20 SE 13 24

*Winds averaged near 20mph for 10 hours from 5pm – 3am.

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Riding Areas
Updated Thu, April 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
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
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
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.