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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
Fri, December 6th, 2019 - 7:00AM
Expires
Sat, December 7th, 2019 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger remains MODERATE in the Alpine due to a buried layer of faceted snow that sits 2-3′ below the snow surface. This layer is still showing signs that an avalanche could be triggered on steep slopes at the high elevations above 3,000′. Below 3,000′ there is a LOW avalanche danger.

*Avalanche danger expected to rise through the weekend in sync with a strong warm storm moving in.

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Fri, December 6th, 2019
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Low (1)
Below Treeline
Below 1,000'
Avalanche risk
No Rating (0)
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

Today should be our last day of cold temperatures before our weather does a complete 180 on us. A large scale system with strong southerly flow is headed in this evening and will bring considerably rising temperatures, gale force winds and heavy precipitation through the weekend. Rain could make it above 2,500′ by Sunday and another pulse looks to pump more warm air and moisture in for Monday and Tuesday. After today, expect rising avalanche danger, wet soggy snow along Turnagain Pass, and if we are lucky, the rain line will not reach our ridgetops. Stay tuned for more details on precip numbers tomorrow morning.

For today however, we are still in a similar avalanche pattern. Our main concern is at the upper elevations above 3,000′ where a person could trigger an avalanche 2-3′ thick breaking near the ground. If skies are clear enough to travel above 3,000′, keep in mind there is a potential weak layer of facets lurking under you. There could be no signs of instability before a slope cracks and releases. Unfortunately, snowpack tests continue to show reactivity in a weak layer of facets just above hard crust. This is keeping our hackles up on high alpine slopes.

High elevation terrain, pictured above, is where our avalanche concerns exist. 

 

Snow pit at 3,200′ on Sunburst shows a thinner section of the snowpack (2.5 feet total depth) and thinner section of the slab (1.5 feet). This pit had the most reactive and concerning stability test results and tells us this layer of faceted snow could create an avalanche. 

Weather
Fri, December 6th, 2019

Yesterday:  Partly cloudy skies were over the region with a trace of snow overnight in areas near Turnagain Arm. Winds shifted from the NW to the east in the morning and have been averaging near 5mph with gusts in the mid-teens. The wind shift brought slightly warmer temperatures, mid-teens along the ridgelines and the low 20’s at the lower elevations.

Today:  Partly cloudy skies, slowly warming temperatures and scattered light snow showers are forecast (to sea level). Only a trace to 2″ of snow is expected today along with a chance for 2-4″ of snow tonight. Winds will continue from an easterly direction and pick up into the 15-25mph range along ridgetops before increasing tonight to the 30-40 mph. Temperatures should rise to the 20’s F at the high elevations (4,000′) and close to 30 F at the low elevations (1,000′).

Tomorrow:  A strong weather system and significant warming trend is on tap for the weekend and into early next week. Heavy snow and rain at sea level is expected along the eastern Kenai and western Prince William Sound. Seward is expected to see several inches of rainfall and Girdwood up to an inch tomorrow. Snow should make it to 1,000′ tomorrow but then turn to rain on Sunday with the snow line rising to 2,000′ or higher by Monday. We’ll be keeping close tabs on this storm so stay tuned!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 18 0 0 15
Summit Lake (1400′) 15 0 0 9
Alyeska Mid (1700′) 17 0 0 18

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 14 NE 5 12
Seattle Ridge (2400′) N/A* N/A* N/A* N/A*

*Seattle Ridge anemometer (wind sensor) is rimed over and the temperature sensor is not functioning. A new temperature sensor is arriving soon and we hope to get it up on the next clear day.

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Riding Areas
Updated Mon, October 26th, 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
Glacier District
Johnson Pass
Closed
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
Closed
Resurrection Pass Trail
Closed
Snug Harbor
Closed
South Fork Snow River Corridor
Closed
Summit Lake
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.