Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, March 18th, 2021 - 7:00AM
Expires
Fri, March 19th, 2021 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE at all elevations.  There is still a chance of triggering a slab avalanche that fails on weak snow buried between 1-3′ feet deep. Additionally, increasing west/northwest winds today may be enough to create some new shallow wind slabs in upper elevation terrain. Watch for blowing snow and changing conditions. Assess the snowpack as you travel, identify areas of concern and evaluate terrain consequences.

LOST LAKE/SNUG/SEWARD: The northwest winds are forecast to be stronger in these areas. Watch for blowing snow and pay attention to terrain selection.

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Heading to Hatcher Pass? Be sure to check the Thursday Conditions Summary at hpavalanche.org.

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Thu, March 18th, 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)
Avalanche Problem 1
  • 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

With sunshine and soft snow, folks that were out yesterday found the pot o’ gold and a shamrock of day. Overall signs are pointing to a snowpack that is trending to green (LOW danger) and that triggering a persistent slab avalanche is becoming unlikely. It has been a week since the last avalanche large enough to bury and kill a person was triggered on our weak layer/crust combination of concern. There have only been a few small wind slab avalanches reported since then. Over the past week there have been a number people out enjoying the snow with no incident. However, completely trusting a snowpack with obvious persistent weak layers is hard as there is always some uncertainty. There are a couple factors keeping the danger elevated today. One being increasing winds and snow available for transport. The other main data point is that for the second day in row skiers backed off of their objective due to a large collapse (whumpf) and then dug down to find a buried sun crust with facets. On Tuesday it was on Orca and yesterday it was on Goat Mountain. This is a sign of instability combined with poor snowpack structure. Observers on Maxs and Magnum yesterday found similar structure on southerly slopes but no collapses while traveling or propagation in snowpack tests.

Here are some things to keep in mind today:

  1. The west/northwest winds are forecast to increase throughout the day. This may add a bit more load and slab over the buried weak layer (more on the winds in Problem 2). The most likely places to trigger an avalanche will be on steep slopes that have seen recent wind-loading, with stiffer snow on the surface.
  2. Southerly slopes with the buried sun crust and facets seem to be more suspect than northerly slopes that just have buried facets and/or surface hoar and no crust.
  3. There is more snow over the buried weak layer in Girdwood, Portage, Placer/Skookum and the northern end of the Pass then there is in the terrain towards the southern end of Pass. Where there is more snow there is the potential to have a deeper slab.
  4. Slab vs. no slab really is the question. If there is just soft snow over the weak snow (with or without the sun crust below) then there is no issue, aside from sluffing. Sussing out if there is a slab is key. Hand pits and small slope tests are good tools for this. One thing that is working in our favor for stability and riding conditions is that the cold temperatures have continued to loosen the surface snow as it facets out.

What to do with this information? As always, pay attention to changing conditions, watch for signs of instability, use good travel protocol, and think about terrain consequences.

Sluffs: Steep slopes that have been sheltered from the wind have around a foot or more of loose snow sitting on top of firm surfaces. It will be easy to trigger dry loose avalanches today, and they can pick up enough volume and speed to carry a person. While it is unlikely they will be big enough to bury you, they can be dangerous if they drag you into terrain traps like cliffs, trees, rocks, or gullies.

Sun effect: Despite cold temperatures and winds, be on the lookout for sun effect on steep southerly slopes, especially under rocky areas at lower elevations.  There is sun crust that formed Tuesday on steep southerly slopes. Watch for the surface snow becoming moist and small roller balls.

Snow pit on Magnum at 3000′ on a south aspect yesterday, 3.17.21. Note the sun crust that is easy to see. We found a layer of small facets both above and below it.

 

 

Avalanche Problem 2
  • 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

The west/northwest winds are expected to increase today which may increase the likelihood of triggering a small wind slab avalanche. These will have the potential to step down to the weak layers discussed above, creating a larger avalanche. As we have mentioned before, this wind flow direction is tricky for Turnagain Pass. It can funnel through the Pass from the south and load north aspects on the non-motorized side, while at the same time load the SE face of Seattle Ridge. It can also split around the Pass and not affect much of the terrain in the heart of Turnagain at all.  This wind pattern also increases through channeled terrain and can be more pronounced in Crow Pass and Portage. Be aware of active wind-loading, and keep an eye open for signs that a slope has been recently loaded. This will feel like stiffer snow at the surface, and may have the appearance of a smooth, rounded pillow. If you experience any collapsing (‘whumpfing’) or cracks shooting out from you or your machine, the snowpack is giving you clear signs that it is capable of avalanching.

Wind texture on the north side of Magnum yesterday, 3.17.21. There was just enough wind in the afternoon to blow a little snow around. The north side was getting loaded from the south (northwest winds being funneled from the south through Turnagain Pass).

Weather
Thu, March 18th, 2021

Yesterday: Skies were partly sunny with light northwest winds and temperatures in the single digits to low teens at upper elevations and mid 20°Fs near sea level. Overnight skies were partly cloudy and temperatures were in the single digits and low teens. Northwest winds were light.

Today: Skies will be partly sunny with a slight chance of flurries in the morning. West/northwest winds will be 5-10 mph increasing in the afternoon to 10-20 mph with gusts into the 30s. Temperatures will be in the single digits to mid teens. Overnight skies will be mostly clear. Northwest winds continue to blow 15-20 mph with gusts into the 30s. Temperatures will be in the single digits.

Tomorrow: Sunny skies with highs in the teens to mid 20°Fs. Winds will be westerly 5-10 mph becoming calm in the afternoon. There looks to be a slight warming trend for the weekend with a slight chance of snow Saturday and sunshine on Sunday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 11 0 0 114
Summit Lake (1400′) 8 0 0 46
Alyeska Mid (1700′) 12 0 0 117

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 2 NW 6 20
Seattle Ridge (2400′) 8 NW 3 15
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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.