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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, January 23rd, 2021 - 7:00AM
Expires
Sun, January 24th, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

A warm, wet and windy weather system is impacting the mountains today and increasing the avalanche danger above 1,000′ to CONSIDERABLE. Freshly formed wind slabs 1-2′ thick are likely to be found and triggered on slopes receiving more than 6″ of new snow with added wind loading. These may also release naturally. At the lower-elevations (near 1,000′), a MODERATE danger exists and small wet snow avalanches are possible on steep slopes and terrain features where rain and/or wet snow is falling. Pay attention to changing conditions and signs of instability.

The National Weather Service has issued a Special Weather Statement for the potential for widespread snowfall for Southcentral today.

SUMMIT LAKE: Extra caution is warranted as any new snow and wind loading will not only create wind slab issues, but there is the potential of an avalanche breaking deeper in the snowpack due to old buried weak layers.

SNUG/LOST LAKE/SEWARD: This storm should sweep by this area as well and increase the avalanche danger. We have limited information for the Seward and Snug zones and would appreciate any eyes out there! Share your observations here.

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Sat, January 23rd, 2021
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)
Avalanche Problem 1
  • 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

A warm and wet storm has pushed into the area this morning. Light to moderate rainfall is occurring below 800-1,000′ with snow above this. The rain snow line could creep up a bit more, to 1200′, before cooling off this afternoon. In the upper elevations, we could see 8-12″ of heavy snow by this evening while almost an inch of rain could fall on snow (or ground) at the lower elevations. Ridgetop winds associated with the precipitation are climbing and forecast to be strong through the day, averaging 40-50mph from the east. What does this all do for our avalanche issues? Well, it all depends on the amount of snow and wind really.

Wind slabs should be the most likely avalanche problem as the higher terrain will see the higher snowfall amounts accompanied by wind. Many of these areas are difficult to access on a day like today, but that said, the possibility of a natural wind slab sending debris into an accessible place in the flats or the trees could catch someone off guard if under steep slopes; for example, under the steep Seattle Ridge gullies. Wind slabs could also be found in the mid-elevation trees if the storm really does put down more than 6″. If headed to these areas, note how much new snow there is and if it’s being blown into fresh slabs.

Even out of the wind, you might see some shallow storm slabs forming as this event is coming in upside down (heavier snow over lighter snow). Both wind or storm slabs could be small and harmless (6″ or less), or in places with more snow/wind, larger and enough to bury a person (1-2′). If braving the rainy and windy roads to head into the hills, it’s a day to really pay attention to the changing weather and signs of instability, such as cracking in the new snow and any signs of recent avalanches.

Cornices: This is a prime cornice building event, sticky warm snow and strong, but not too strong winds. Natural cornice falls are possible, which often turn out to be the main driver for triggering a wind slab in the upper elevations.

Wet snow avalanches: If we really do get rain up to 1,200′, the snow could get slushy and small wet loose avalanches could be triggered in these lower elevations.

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glide cracks continue to open around the region. We are keeping track of where known glide cracks are. So far, these are not in areas commonly traveled by recreating public. Here is a list:

Girdwood Valley: Goat shoulder, Raggedtop lower SE shoulder, the far NE end of Penguin Ridge above Girdwood.

Turnagain Pass: The far northern end and SE aspect of Seattle Ridge, Warmup Bowl (-1 Bowl) NE aspect on the backside of Seattle Ridge.

Summit Lake: Gilpatrick’s S face, Devil’s Creek south side.

Weather
Sat, January 23rd, 2021

Yesterday: Cloudy to broken skies were over the region. Between 1-3″ of snow fell in the early morning before tapper off. The rain/snow line was roughly 500-600′. Ridgetop winds were moderate, averaging 10-20mph during the day, before increasing last night into the 35-40-mph range from the east. Temperatures continue to be warm, in the upper 30’sF at sea level and the mid 20’sF along the ridgetops.

Today: A weather system has moved in this morning from the Gulf. Widespread snow showers above 1,200′ and rain below this is expected through the day. Accumulations are expected to be 6-12″ in the Alpine and .5-1″ of rain at sea level, the higher amounts expected nearest Turnagain Arm. Ridgetop east winds will remain strong, averaging 35-45mph. Temperatures should climb to 40F at sea level and the upper 20’sF along ridgelines.

Tomorrow: Tapering snow showers are expected tomorrow morning before skies begin to clear during the day. Ridgetop winds are forecast to shift westerly and then northerly bringing in cooler air. These should remain somewhat elevated in the 15-25mph range. Temperatures finally look to dip below 30F at sea level and below 20F along ridgetops. Models are hinting at continued dry weather and mostly clear skies for Monday and Tuesday, stay tuned.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32 0 0.1 129
Summit Lake (1400′) 31 0 0 44
Alyeska Mid (1700′) 32 3 0.3 116

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 NE 22 63
Seattle Ridge (2400′) 27 SE 14 26
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Riding Areas
Updated Tue, June 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
Closed
Placer River
Closed
It is packrafting and jetboat season!
Skookum Drainage
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
Turnagain Pass
Closed
Closed as of June 1. 188 day season, that\'s a wrap!
Twentymile
Closed
It is packrafting and jetboat season!
Seward District
Carter Lake
Closed
Closes May 1.
Lost Lake Trail
Closed
Closes May 1.
Primrose Trail
Closed
Closes May 1.
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season. Will be open for moto use in the 21/22\\\' winter season as per the CNF Forest plan.
Snug Harbor
Closed
Closes May 16th.
South Fork Snow River Corridor
Closed
Closes May 1.
Summit Lake
Closed
Closes May 1.

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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.