Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, November 23rd, 2021 - 7:00AM
Expires
Wed, November 24th, 2021 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger today is CONSIDERABLE  above 2500′. New snow and increasing winds will make it likely a person could trigger a wind slab avalanche up to 2′ deep, and it is possible we will see some natural activity. Since this new snow is falling on weak surfaces, avalanches will also be possible on slopes that haven’t seen wind loading. Cautious route finding is key today, which means avoiding steep slopes, traveling one at a time, and watching partners from safe spots.

The danger will be MODERATE below 2500′, where lighter winds will make for slightly more stable conditions, but triggering an avalanche will still be possible. Be on the lookout for pockets of wind loading, especially in gullies and rollovers, and be aware of the possibility of triggering storm slab avalanches a foot deep in steep terrain.

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Tue, November 23rd, 2021
Alpine
Above 2,500'
Considerable (3)
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
Considerable (3)
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
  • 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

After nine days of cold and clear weather, snow has returned to the area. Stations are showing .5″- 1″ of snow water equivalent (SWE) overnight, which could translate to over a foot of snow, especially at higher elevations. Another 4-6″ snow is expected during the day, with easterly winds expected to pick up to 25-30 mph, approaching 40 mph at the higher ridgetops. This active weather, combined with a mixed bag of weak, sugary facets on the old snow surface, will combine to make dangerous avalanche conditions. This will be especially true above treeline (~2500′) and close to the Turnagain arm, where winds will be the strongest.

Cautious route finding is the name of the game today, especially in the upper elevations. Wind loaded slopes below ridgelines, convexities, and in gullies will be the most suspect terrain. However, because this new snow is falling on weak surfaces, it will be important to approach all steep terrain with caution. The wind slabs that formed earlier in the week will now be much harder to identify, and since they are sitting on top of weak snow they may still be reactive. As always, be smart with your travel by only putting one person on a slope at a time and watching your partners from safe spots.

New snow and wind slabs will be forming on this poor structure. Cautious route finding will be important today. Snowpit from Raggedtop, 11.22.2021

Avalanche Problem 2
  • 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

This round of snow has fallen on weak surfaces, which will make it possible to trigger avalanches on slopes that have been sheltered from the wind. Weather stations are acting up this morning, so it is hard to say exactly how much snow has fallen, but best estimates based on the snow water equivalent (SWE), and by looking at the front yard this morning (see photo below) would put snow totals at a foot or more in some parts of the advisory area. This pulse of moisture will require stepping back from how we have been approaching terrain for the past week, since sheltered slopes will now require a little more attention.

Pay attention to warning signs showing instability as you travel. This will include cracks shooting out from your feet, and fresh avalanches. You might use small test slopes to see how the storm snow is behaving on top of the weak older snow. As mentioned above, play the odds in your favor by only putting one person on a slope at a time, and watch your partners from safe spots.

Dry loose avalanches: All of this low-density snow on top of loose sugar will easily move in steep terrain today. Sheltered slopes will have up to another foot of soft snow below this storm snow, which means sluffs could pick up a large volume of snow. Be aware of dry loose avalanches today, especially in higher consequence terrain above rocks, trees, cliffs, or in gullies.

Impromptu snow stake on our deck in Girdwood this morning. Very low-density snow might not be getting accurate readings at the weather stations… 11.23.2021

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

We have seen continued glide activity in and around the advisory area. The glide avalanches seem to have slowed down over the past few days, but we still cannot rule them out entirely. Timing of glide releases is impossible to predict, and they are very large and destructive. Be aware of these monsters, and limit the amount of time you spend traveling below glide cracks.

Weather
Tue, November 23rd, 2021

Yesterday: Temperatures were in the single digits to low teens, with light snow on and off during the day. Winds were light out of the north to northwest. Snowfall picked up overnight, with 6-12″ snow as of 6:00 a.m.

Today: Easterly winds are expected to pick up today, blowing 25-30 mph and approaching 40 mph in the highest terrain and near the Turnagain arm. Temperatures will get up into the mid teens F. Snow showers during the day could bring another 4-6″ snow. Overnight low temperatures will be in the single digits to low teens F.

Tomorrow: Another pulse of moisture during the day could bring another 2-4″ snow. Winds will calm to 5-10 mph by the morning, but may start to pick up again late in the afternoon and overnight. It is looking like there could be another round of snow right on the heels of this system, and there is some uncertainty as to just how much (if any) we will get. Stay tuned for more.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 3 N/A 1.0 N/A
Summit Lake (1400′) -6 tr tr 10
Alyeska Mid (1700′) 4 0* 0* N/A*

*   Station not yet reporting snow data. 10-12″ cold smoke on the ground in Girdwood as of 6:00 a.m.

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 4 NW-NE* 12* 30*
Seattle Ridge (2400′) -2 NNE 5-10 9

*Winds shifted from westerly to easterly and increased around 10:00 p.m. last night.

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Riding Areas
Updated Sat, November 27th, 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
Closed
Closed
Placer River
Closed
Closed
Skookum Drainage
Closed
Closed
Turnagain Pass
Open
Open as of Saturday, Nov 27. Be aware of early season hazards (alders/creeks) and open water.
Twentymile
Closed
Closed
Seward District
Carter Lake
Closed
Closed
Lost Lake Trail
Closed
Closed
Primrose Trail
Closed
Closed
Resurrection Pass Trail
Closed
Closed. Scheduled to open December 1 (if snow cover conditions allow) for motorized use in the 21/22 winter season as per the CNF Forest plan.
Snug Harbor
Closed
Closed
South Fork Snow River Corridor
Closed
Closed
Summit Lake
Closed
Closed

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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.