Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, December 29th, 2021 - 7:00AM
Expires
Thu, December 30th, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger will remain MODERATE above 1,000′ on all aspects. Cooling temperatures will be helping to freeze and stabilize the snowpack, yet strong westerly winds may be enough to create new wind slabs in the Alpine. Be cautious on slopes that are still moist/wet from the warm temperatures, especially where the snowpack is shallow, as there still could be a chance for triggering a large slab avalanche breaking in buried weak layers.

Below 1,000′ the danger is LOW and triggering an avalanche is unlikely.

SUMMIT LAKE:  Extra caution is recommended as the snowpack is weaker and shallower. Several large avalanches occurred in this area on Sunday that broke into buried weak layers and human triggered avalanches remain possible.

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Wed, December 29th, 2021
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
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
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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

It is a bit of a transition day for the snowpack as colder air is moving in with sustained strong west winds. Overnight, temperatures have dropped to the mid 20’sF in the higher terrain and through the day, valley bottoms should see numbers near 30F. The wet layer of snow that capped the snowpack to ridgetops should now be a crust, or very soon will be. From the little we know now, the crust is variable; very thin to maybe an inch at Turnagain Pass and thicker to the south near Summit Lake. Not to mention, the crust should get thicker with elevation as warmer conditions were seen along the ridgelines vs the cooler air that was trapped in valley bottoms. Furthermore, the light rain that fell yesterday evening will have only added to the wet layer. We will see in the next couple days what damage this crust has done to the ski and riding quality.

The other thing that will give us some insight into how thick the crust is, is if the strong west winds forecast through the day will be able to transport any snow. Sunburst weather station gusted to 62mph around midnight and other stations have been reporting these strong winds. If you do head out, watch for any signs the winds are able to move snow. If this is the case, touchy wind slabs may be found, likely sitting on a crust.

Thin melt-freeze crust capping dry snow, near 1100′ on Eddie’s at Turnagain Pass. Allen Dahl, 12.28.21.

 

The other, and more uncertain avalanche issue, is what the buried weak layers are doing, or not doing, as the surface freezes up. These weak layers are under 3-5+’ of a dense layer of snow at Turnagain Pass, but are only under a couple feet on the southern end of the forecast zone and even less in places at Summit Lake. Although there were no avalanches that we know of the past two days, there were several large natural avalanches on Sunday, the first warm day, breaking in these old weak layers. One was just inside our forecast zone on Twin Peaks and the others were to the south in Summit Lake.

Moving forward, signs are all showing that at Turnagain Pass where the snowpack is thicker, it’s becoming very unlikely that a person could trigger a deep slab avalanche. The south end of the forecast zone and areas with a shallower snowpack are still a concern until they freeze up. Once they do it’ll be a question as to how stout surface crusts are and if any water that percolated under the surface and into the weak layers freeze, in order to determine if the weak layers are healed up or not. For today, be wary of these shallow zones if they are still harboring wet snow.

This all said, there is hope for some better snow quality for New Year’s as several inches of snow could fall early Friday morning. Cross your fingers!

 

Weather
Wed, December 29th, 2021

Yesterday:  Mostly clear skies gave way to cloudy skies and light rain to ridgetops yesterday evening. Around 0.2″ were seen at most stations. Ridgetop winds were 5-10mph from the west during the day before bumping up to 15-25mph with gusts near 60mph overnight. Temperatures were in the upper 30’s to 40 during the day before they dropped along ridgetops with the bump in winds and are slowly dropping in valley bottoms this morning.

Today:  Partly cloudy skies, cooling temperatures, and breezy west winds are in store. Temperatures should make it to the teens along ridgelines and near 30F in valley bottoms. Ridgetop winds will remain northwesterly and should stay in 15-25mph with gusts 40-50mph.

Tomorrow:  Another mostly clear sky day is forecast tomorrow. Winds should be light and variable and slowly backing to the east ahead of a weather system setting up for Friday, New Year’s Eve. Right now it looks like we could get 3-6″ of snow to sea level. Stay tuned!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 38 rain 0.2 66
Summit Lake (1400′) 33 rain 0.2 21
Alyeska Mid (1700′) 37 rain 0.2 38

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 31 W 13 62
Seattle Ridge (2400′) 33 NW 11 39
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Riding Areas
Updated Wed, December 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
Open as of Dec 1st.
Placer River
Open
Open as of Dec 1st. Limited parking due to Portage curve construction.
Skookum Drainage
Open
Open as of Dec 1st. Limited parking due to Portage curve construction.
Turnagain Pass
Open
Open as of Saturday, Nov 27. Be aware of early season hazards (alders/creeks) and open water.
Twentymile
Open
Open as of Dec 1st.
Seward District
Carter Lake
Open
Open as of Dec 1st.
Lost Lake Trail
Open
Open as of Dec 1st.
Primrose Trail
Open
Open as of Dec 1st.
Resurrection Pass Trail
Open
Open as of Dec 1st.
Snug Harbor
Open
Open as of Dec 1st.
South Fork Snow River Corridor
Open
Open as of Dec 1st.
Summit Lake
Open
Open as of Dec 1st.

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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.