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Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, March 25th, 2020 - 7:00AM
Expires
Thu, March 26th, 2020 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

Warm and wet weather moving in will keep the avalanche danger MODERATE for triggering a wet loose avalanche below 2,500′. Above this, triggering a lingering wind slab is still possible. Additionally, give cornices a wide berth.

SUMMIT LAKE:  This area harbors a shallower snowpack with weak snow in the mid and base of the pack. Triggering a larger slab is possible and extra caution is advised.

PORTAGE VALLEY/Byron Glacier Trail:  It’s that time of year to avoid avalanche runout zones along summer trails. Springtime avalanches can hit areas such as the Byron Glacier ice caves.

***Roof Avalanches:  Heads up. Roofs are still shedding remaining snow.

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Wed, March 25th, 2020
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
  • Wet Loose
    Wet Loose
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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

Clouds have moved in this morning along with warm temperatures and a shot for a little snow. This quick hitting system will impact Anchorage and Hatcher Pass more than Turnagain, yet we should see some rain mixing with snow in Girdwood and possibly an inch of snow at 1,000′ on Turnagain Pass. If we’re lucky, we’ll see a couple inches at the high elevations. Although the new snow snow/rain amounts are too small (0.1″ water) to add weight to the snowpack, it will be the temperatures that contribute to avalanche danger today.

As temperatures remain warm and above freezing from around 2,500′ and below, we can expect the surface crusts to be present, but on the softer side this morning. Daytime heating is likely to soften them more and once your snowmachine/skis/splitboard starts punching deep into the snowpack, it’s time to stay off steep slopes. This is when wet loose avalanches will become possible to trigger. These wet sluffs could start quite small, with a person, a roller ball or piece of snow falling from a tree or rocky cliff. If conditions are right, they can entrain enough snow to cause a larger avalanche than expected. This is an easy problem to see if we make sure to watch for it.

A small wet loose avalanche on Seattle Ridge that was triggered by a piece of snow falling off a tree and onto a steep portion of the slope yesterday.

 

Wet Slabs:  As we head into spring, keep in mind that the snowpack is warming as a whole. At elevations below 2,500′ areas are already seeing wet/moist snow throughout the pack. Once this occurs, we can start seeing wet slab avalanches. The photo below is from the Summit Lake area and shows a large collapse in weak faceted snow that propagated far uphill yesterday. If this slope was steep enough to slide a wet slab avalanche would have resulted. This issue is more likely where the snowpack is shallow, such as Summit Lake.

A collapse in weak faceted snow triggered by a skier in the Summit Lake area yesterday (elevation 1,800′). Note how the snowpack dropped a few inches and the crack can be seen extending far upslope. This was in the Treeline band below 2,500′. 3.24.20. Photo: Paul Wunnicke

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

Watch for lingering stiff wind slabs on steep slopes in the Alpine. These are from the strong winds on Sunday and Monday. These slabs could be sitting on buried surface hoar or older sun crust and may still be possible to trigger. Warm temperatures can also increase the likelihood of triggering.

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

In shallow snowpack zones, triggering a larger slab that breaks in weak snow in the mid and base of the snowpack is still a concern. This is at the higher elevations where drier snow exists. The recent warm weather is changing the character of the slab on top, which can increase the chance a person can initiate a failure in the weak facets below and create an avalanche. Areas with a shallow snowpack are on the south end of Turnagain Pass to Summit Lake.

A natural avalanche on the southwest facing couloir of Templeton in the Summit Lake area. Note how the avalanche ‘stepped down’ into deeper weak layers. This occurred during the Sunday/Monday outflow wind event. Photo taken 3.24.20 by Paul Wunnicke.

Weather
Wed, March 25th, 2020

Yesterday:  Mostly sunny skies with high clouds were over the region. Ridgetop winds were light and westerly (5-10mph). Temperatures rose to 30°F at 4,000′ and into the mid 40’s°F at sea level.

Today:  Cloudy skies are over the region as a warm weather system moves through. Light snowfall should add around an inch of snow above 1,000′ today and a rain/snow mix below that could transition to mostly rain at sea level. Ridgetop winds are shifting more southerly this morning and should be in the 5-15 mph range from the southwest before swinging back northwesterly tonight bringing drier air into the area. Temperatures are forecast to be near 30°F along the ridgelines and 40°F at sea level.

Tomorrow:  Mostly sunny skies with light northwesterly winds are forecast tomorrow as the moist weather moves out tonight. Another round of precipitation and snowfall for areas above 1000′ heads in for Friday and into the weekend. Stay tuned.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 38 0 0 66
Summit Lake (1400′) 39 0 0 31
Alyeska Mid (1700′) 35 0 0 75

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 30 W 9 21
Seattle Ridge (2400′) 33 NW 3 8
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Riding Areas
Updated Fri, May 01st, 2020

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
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Closed
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Closed as of May 1. Thanks for a fun, safe season!
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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.