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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, February 24th, 2018 - 7:00AM
Expires
Sun, February 25th, 2018 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is  MODERATE  above 1,000′ on all aspects. Triggering an isolated wind slab or a more connected persistent slab 1-2′ deep is possible today. Additionally, weak layers deeper in the snowpack may still be triggered, creating a larger avalanche. With new snow and wind in the forecast today pay attention to changing conditions.  

Read the Summit Summary  HERE.  

 

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Sat, February 24th, 2018
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
  • 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
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. 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, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

Triggering a slab avalanche 1-2+ feet deep remains possible above 1000’ due several weak layers buried within the snowpack. A layer of buried surface hoar from Jan. 21st continues to show signs of reactivity in the upper elevations, and a layer of facets over a melt-freeze crust is suspect in the mid elevation band. The slab ranges from hard to soft depending on exposure to recent winds.  The Northwest winds overnight Thursday blew the 3-4” inches of new snow into stiff wind crusts. As noted yesterday this wind direction can funnel through Turnagain Pass from a variety of directions causing unusual wind loading patterns that were evident traveling on Sunburst. Another 4-5″ of light snow fell overnight and today we may pick up an additional 2-4.” This combined with escalating Northwest winds may add more slab and stress to the snowpack. Be suspect of hard snow under the new soft snow, especially where the slab is fully supportable or hollow sounding. Red flags like shooting cracks or “whumpfing” may not be present before a slope releases. Evaluate the terrain for consequences and be aware of places that haven’t seen much traffic. These less traveled places are more suspect for triggering a more connected slab. 

Deep Persistent Slabs: Keep in mind that there are deeper persistent layers that could ‘wake up’ if you find the wrong spot above 3,000′ in the Alpine. At these high elevations, old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is most pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass. 

Avalanche Problem 2
  • 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
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. 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, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

Triggering a wind slab is possible today on steep unsupported terrain features where winds have been transporting snow. These slabs could range from tender and soft with new snow overnight being moved by winds today or hard and supportable due to the strong winds Thursday night. Remember the hard wind affected snow will be under the new snow. It may be harder to pick out wind loaded areas with the fresh coating of snow on top and slab could release from above once committed to a steep slope. 

Sunshine:  If the clouds break earlier than expected today remember that it is that time of year when we need to pay attention to the sun.  The sun can heat up Southerly aspects, and melt surface snow and cause small point releases in the loose new snow. This will be more of a concern if winds are calm today, which may be the case this afternoon. This heating can also cause a slab sitting on a weak layer to become more reactive. Avoid steep solar aspect if you notice the surface snow becoming moist or you see roller balls or point releases under rocks. 

Wind effect on the Sunburst ridge yesterday

 Wind crust on Sunburst easily sliding off of snow below. New snow and wind loading today could turn this into a wind slab. 

Weather
Sat, February 24th, 2018

Yesterday started clear and became cloudy by the evening. Temperatures were in the teens to low 20Fs. Winds started out Northwesterly and gusted into the 60s on Seattle Ridge in the morning. They switched to the Southeast overnight and blew in the teens gusting into the 30s.  

4-5″ of light snow fell overnight with an additional 2-4″ in the forecast today. Temperatures will be in the teens to mid 20Fs. Southwinds winds are forecast to shift back to the Northwest in the afternoon blowing 10-20 mph with gusts into the 30s.    

Sunshine is on tap for tomorrow and then a chance of snow again Sunday.   This pattern of smaller storms followed by sunshine looks to continue into next week.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 22    4  0.3  68
Summit Lake (1400′) 18      5  0.3  30
Alyeska Mid (1700′)  20      5  0.2  61

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  10  W-E  8 38  
Seattle Ridge (2400′)  16 NW-SE   20    62    
Observations
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Riding Areas
Updated Wed, December 11th, 2019

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
Closed.
Placer River
Closed
Closed.
Skookum Drainage
Closed
Closed.
Turnagain Pass
Closed
Closed.
Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
Closed.
Lost Lake Trail
Closed
Closed.
Primrose Trail
Closed
Closed.
Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
Closed.
South Fork Snow River Corridor
Closed
Closed.
Summit Lake
Closed
Closed.

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