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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, November 27th, 2018 - 7:00AM
Expires
Wed, November 28th, 2018 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

As wet and stormy weather continues today the avalanche danger remains HIGH in the Alpine. With additional snowfall and wind loading natural avalanches are likely.  Avalanches at upper elevations may run into terrain below keeping the danger at CONSIDERABLE for the Treeline elevation band. Human triggered avalanches are very likely above the rain/snow line (approximately 2500′). Travel above treeline is not recommended.  

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Tue, November 27th, 2018
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
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
  • 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

With the active weather the avalanche danger remains elevated. Snow at upper elevations and rain at lower elevations is expected to continue today. Rain/snow line is forecast to be around 2500′. Winds are forecast to be easterly with gusts into the 40s.  Our road observations yesterday had limited visibility but a few wet loose avalanches were observed to have run in the mid-elevation band. Rain continues to wash away the snow that fell on Saturday night in this elevation band. 

Water totals at the mid-elevation snow stations for this soggy storm cycle:

  • Girdwood Valley at 1,700′:  4″ of water equivalent 
  • Turnagain Pass at 1,880′:  3″ of water equivalent
  • Summit Lake at 1,400′: 0.9″ of water equivalent 

If we convert the water to snow at upper elevations we have a significant load. We are uncertain at this point about avalanche activity in the Alpine. However snow continues to fall, the winds are sustained and we know this is loading older layers of snow. With this recipe we have to expect storm slab avalanches. 

Rookie Hill with a few small wet loose avalanches in the channeled terrain on Seattle Ridge. November 26, 2018, Photo: Wendy Wagner

Tincan: Snow that fell Saturday night in the mid-elevation band getting rained on. November 26, 2018. Photo: Wendy Wagner 

Weather
Tue, November 27th, 2018

Yesterday:  Rain and snow throughout the day. Rain/snowline was around 2500′. Temperatures were in the high to mid 30Fs at lower elevations and low 30Fs to high 20Fs at upper elevations. Winds were easterly 15-25 mph with gusts into the 40s.  

Today:  As a low in the Gulf continues to push moisture and warm air into the region rain and snow showers will continue. Half to three quarters of an inch of water is forecast to fall. Rain/snowline will remain around 2500′ before lowering Wednesday as cooler air moves in. Winds will be from the E-SE 20-30 mph with gusts into the 40s. Temperatures will be in the 40Fs to high 20Fs depending on elevation.  

Tomorrow:  A trough bringing cooler air is forecast to push up Cook Inlet with the potential to bring snow to Anchorage and Hatcher Pass. The advisory area should see a shift to snow showers with cooling temperatures later in the day into Thursday. The timing on all this is fairly uncertain as the weather models are not in agreement.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 36   0    0.8  13
Summit Lake (1400′) 35   0  

 0.4

 0
Alyeska Mid (1700′) 36   0    1.59  0

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  29  NE 16    50
Seattle Ridge (2400′)  32  E 11  40
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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
Glacier District
Johnson Pass
Closed
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Closed as of May 1. Thanks for a fun, safe season!
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.