Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, April 16th, 2021 - 7:00AM
Expires
Sat, April 17th, 2021 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE, and expected to rise to HIGH on southerly aspects this afternoon as we experience the first major warming event after heavy snowfall earlier in the week. It is very likely a person will be able to trigger a large avalanche as the mostly dry storm snow undergoes rapid warming, and we are also likely to see large natural avalanches this afternoon as temperatures rise and the sun comes out. These avalanches will be large enough to run into valley bottoms, which will make it important to avoid travelling on or below steep southerly slopes. Although the warming will not be as intense on shaded slopes, it is still likely a person could trigger a large avalanche within the recent storm snow, which can be 1-3′ deep at Turnagain Pass and 2-4′ deep near Girdwood.

PORTAGE VALLEY: Large natural avalanches have the potential to bury popular hiking trails like the Byron Glacier or Portage Pass trails. Travel on trails that cross under steep slopes is not recommended.

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Fri, April 16th, 2021
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
High (4)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
High (4)
Below Treeline
Below 1,000'
Avalanche risk
High (4)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Seattle Ridge: Multiple loose and slab avalanches were visible from this week’s storm snow on Seattle Ridge.

Summit Lakes: Several natural avalanches were noted near Roaring Ridge, along with a glide avalanche on Gilpatrick.

Alyeska: Avalanche hazard reduction produced avalanches at Alyeska.

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Don’t let the pleasant weather fool you– the snowpack is about to experience a rapid transition from dry to wet, and avalanche conditions will become very dangerous. There is a chance we could see just about every type of avalanche in the next few days, and the activity is expected to start this afternoon. The mountains near Girdwood have gotten 2-4′ snow this week, while Turnagain Pass has seen 1-3′. This storm snow is mostly dry above 1700′, and will become increasingly unstable as temperatures rise and the sun comes out to cook the snow. It will be tempting to get up into higher elevations to seek out drier snow, but the conditions may actually be the most dangerous where storm totals were higher and the new snow has not yet seen any melt or refreeze prior to the rapid warming expected today. Keep an eye out for classic signs of instability like shooting cracks and collapsing (‘whumpfing’) throughout the day, clear indicators that the snowpack is capable of producing an avalanche. Although the exact timing of these avalanches will be difficult to  predict, we can expect the likelihood of large natural and human-triggered avalanches to increase this afternoon.

We are entering uncharted territory for this season, and we have seen similar conditions result in large avalanches in the past. Avoid travelling on or below steep southerly slopes, especially later in the day, and use caution while approaching northerly aspects. Elevated danger is expected to continue through the weekend, as we are expecting more sunshine and continued warm temperatures.

Cornices: Warming temperatures will start to weaken large cornices, increasing the likelihood of cornice fall. As always, give cornices plenty of space and limit time spent travelling below them. A falling cornice could trigger a large avalanche today.

Loose Snow Avalanches: These will become more likely when the sun makes an appearance. They may be triggered naturally as snow falls off rocks and trees that heat up in the sun, or they could be triggered by a person in steep terrain. A relatively small loose snow avalanche will be likely to trigger a larger slab avalanche today.

Roof Avalanches: For buildings that have not already shed their snow, warming temperatures and melting snow will increase the likelihood of roof avalanches today. Pay attention to children and pets, and be mindful of where you park your car.

Recent avalanche activity on Seattle Ridge, likely within past 3 days. 04.15.2021

Avalanche Problem 2
  • Wet Slab
    Wet Slab
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Wet Slab
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

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

At elevations below 1700′, most of this week’s storm snow is already moist or wet. Mostly clear skies and cool temperatures overnight have allowed the snow surface to refreeze, which will improve stability for the first half of the day. But be aware of quickly deteriorating stability as temperatures rise and the snowpack softens this afternoon. It will become likely a person can trigger an avalanche in these lower elevations, and it may involve weak layers deeper in the snowpack (see problem 3).

Glide Avalanches: Two new glide releases were noted yesterday, and we will likely see similar activity today. Avoid travelling below glide cracks since they can release suddenly and without warning.

Glide avalanche in the Skookum Valley. 04.15.2021

Avalanche Problem 3
  • 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

The persistent weak layers buried in the upper surface have now experienced a significant loading event, and may start to see meltwater this afternoon. Both of these factors are increasing the likelihood of natural and human-triggered avalanches failing on multiple layers of buried surface hoar and near-surface facets. If we do see avalanches failing on these weak layers, they will be large and destructive. This problem will be important to keep in mind on all aspects, since it is not necessarily related only to warming, but also to the recent loading event.

It looks like spring is making a dramatic appearance to our advisory area. This rapid change means we can expect to see large avalanches, although the exact timing may be difficult to nail down. The best way to navigate the current avalanche conditions is by being extra conservative with your terrain choices, especially by entirely avoiding avalanche terrain on southerly slopes.

Weather
Fri, April 16th, 2021

Yesterday: Temperatures reached the upper 20s F at upper elevations and up to the low 40s F in the valleys under mostly cloudy skies with some brief periods of sun. We saw some snow flurries and mist during the day, but it did not amount to any accumulation. Winds were light out of the east at 5-15 mph, with lighter speeds in the afternoon.

Today: Temperatures are expected to rise to the mid-30s to low 40s F under mostly sunny skies. Winds are going to be light out of the northeast at around 5 mph or less. No precipitation is expected. Overnight lows will drop down to the low to upper 20s under clear skies.

Tomorrow: Another warm day is expected tomorrow, with temperatures in the high 30s to high 40s F, and even pushing close to 50 F in the valleys. Skies are expected to be mostly sunny, with a light easterly wind at 5-10 mph.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 36 tr tr 112
Summit Lake (1400′) 35 tr tr 44
Alyeska Mid (1700′) 35 tr tr 131

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24 ENE 9 28
Seattle Ridge (2400′) 30 N/A N/A N/A

*The Seattle Ridge anemometer has not reported any wind data in the past 24 hours, likely because it is covered in rime.

Observations
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Riding Areas
Updated Sat, May 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
North end of Johnson Pass Trail is open into May as conditions warrant.
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
Open
Open into May as conditions warrant.
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.
Snug Harbor
Open
Open into May as conditions warrant.
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.