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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, December 28th, 2022 - 7:00AM
Expires
Thu, December 29th, 2022 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE at elevations above 1,000′. The Christmas storm has moved out and the mountains are still adjusting to the impact. Human triggered wind slab and storm slab avalanches, 2-4′ thick, could be likely at the mid and upper elevations. Avalanches could be larger than expected if they break in older weak layers in the snowpack. The danger is MODERATE below 1,000′ for wet loose avalanches in places the wet snow has not begun to freeze yet.

*A cautious mindset is recommended if traveling in the backcountry. There is a lot of uncertainty as to how well the new snow is stabilizing or not. Please let us know what you see, we are trying to gather as much data before the next big storm hits this weekend. Thanks!

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Wed, December 28th, 2022
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
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
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

A natural avalanche cycle occurred two days ago during the peak of the Christmas Storm. However, we do not know yet the extent of the avalanche cycle or if any avalanches occurred yesterday.

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Aspect/Elevation
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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.

Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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

For anyone headed out today, there will be several things to watch for. As mentioned above, we have not been able to get into the mountains yet and many unknowns exist. First, if visibility is good enough, are there any signs of recent avalanches? Crowns may be filled in by winds, but can you see debris piles? As you travel, do you feel/hear any collapsing (whumpfing)? Is the snow cracking around you? Are the ridgetop winds still blowing enough to be transporting snow and forming wind slabs? Essentially, looking for those basic Red Flags.

Other things to pay attention to is whether the wet snow surface has frozen, or is freezing. Rain may have fell as high as the top of the treeline so surface conditions could be interesting. If the surface has turned to a crust, avalanches are not likely to occur as the crust locks the snow into place. If there are steep slopes with wet saturated snow, wet loose avalanches could be triggered.

At the higher elevations, above the wet or crusty surface snow, look for how much snow did fall. Quick hand pits can be really useful for this unless the new snow is 2 or more feet deep. In this case, a shovel may be needed to dig in and see where the new snow ends and the older snow begins. It will be the higher elevations, where only snow fell, that should be the most likely place to trigger an avalanche. Both wind slabs and storm slabs could be lurking. The size of the avalanche will depend on the amount of new snow, as deep as 2-4′ in wind loaded areas. The new snow fell on a generally weak surface and it may take more than a couple days for it to bond. Easing into terrain, sticking to slopes 30 degrees or less, and not ignoring any red flags will be good ways to manage potential avalanche issues.

Storm totals for the Christmas Storm (12.25 through 12.27):

Turnagain Pass-     Rain 1.5-2″ below 2,000′, roughly 1.5-2 feet of snow above 3,000′
Girdwood Valley-   Rain 2-2.5″ below 2,000′, estimated 2-2.5 feet of snow above 3,000′
Summit Lake-         Rain ~1″ below 2,000′, roughly a foot of snow above 3,000′

*Note, the rain/snow line may have reached as high as 3,000′ at one point during the Christmas storm, but we think it was generally around 2,000′.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Aspect/Elevation
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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.

Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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

Until we know more, we are concerned the old weak faceted snow that sits above and below the Thanksgiving crust could still be a problem. We still have no information regarding the avalanches that occurred during the storm and if any were able to overload and release in these older layers. If a person was to trigger an avalanche that broke in these layers, the avalanche could be very large and dangerous. Estimated depths of the slab would be in the 3-5′ range. It would be most likely to happen above the rain/snow line where only snow fell. In short an avalanche like this is nothing to mess with, hence our caution.

Weather
Wed, December 28th, 2022

Yesterday:  The Christmas storm moved out yesterday morning and most the day was filled with cloudy skies and intermittent light rain (snow above 1,500′). It looks like only 1-3″ of snow fell at the higher elevations. Ridgetop winds were easterly averaging 10-20mph with gusts in the 40’s. Temperatures have hovered in the mid 30’s at the lower elevations and in the mid 20’F along ridgetops.

Today:  Continued cloudy skies with light precipitation is expected today. Above ~500′ 2-3″ of snow could fall with light rain below this. Ridgetop winds will remain easterly in the 10-20mph range and expected to pick up slightly this evening. Temperatures are on a slight cooling trend with low elevations sitting near 32F at the higher elevations in the low 20’sF.

Tomorrow:  Cloudy skies, the chance for light precipitation, and moderate easterly ridgetop winds should remain through Friday. The next strong storm is looking to head in for the weekend, peaking on the New Year, with 2-3 feet of new snow possibly by Monday. We’ll see how this system develops, but right now the rain/snow line looks to be close to 1000′ for the event.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32 1 0.1 30
Summit Lake (1400′) 32 0 0 28
Alyeska Mid (1700′) 32 trace 0,1 36
Bear Valley – Portage (132′) 39 0 0.9

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24 NE 14 43
Seattle Ridge (2400′) 27 SE 15 8
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Riding Areas
Updated Fri, January 06th, 2023

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
Opened Dec 13th.
Placer River
Closed
Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Skookum Drainage
Closed
Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Turnagain Pass
Open
Opened Dec 13th.
Twentymile
Closed
Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Seward District
Carter Lake
Open
Opened Dec 13th.
Lost Lake Trail
Open
Opened Dec 13th.
Primrose Trail
Open
Opened Dec 13th.
Resurrection Pass Trail
Closed
Closed to motorized use for the 2022/23 winter season per Forest Plan. Open next season.
Snug Harbor
Open
Opened Dec 13th.
South Fork Snow River Corridor
Open
Opened Dec 13th.
Summit Lake
Open
Opened Dec 13th.

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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.