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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, April 17th, 2018 - 7:00AM
Expires
Wed, April 18th, 2018 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger is  LOW  this morning and may rise to  MODERATE  in the afternoon. Triggering a small to large wet avalanche will be possible with daily warming on sunlit aspects or with rain at lower elevations. In the Alpine, triggering a slab avalanche 1-2′ thick remains possible above 3000′ on shaded aspects. Give cornices extra space.  

WEDNESDAY AVALANCHE OUTLOOK:
No avalanche forecast will be issued tomorrow, Wednesday April 18th. The avalanche hazard will be MODERATE. Watch for changing conditions as snow and rain fall and wind speeds increase. Pay attention to how the new snow is bonding to the melt-freeze crusts. If precipitation amounts are higher than forecast the danger may rise to CONSIDERABLE.  

Special Announcements

The snow is melting fast at lower elevations and the following areas have been closed to snowmachining on the Chugach National Forest: Placer, Twentymile, Snow River, Primrose, Lost Lake. Snug Harbor access to Lost Lake remains open at this time. Keep an eye on the riding status at the bottom of this page for current updates.  

Be aware some summer hiking trails like Byron Glacier trail in Portage have steep avalanche terrain above them and the potential for a natural avalanche exists later in the day on slopes getting lots of sun in the afternoon or if it rains.  

CNFAIC is transitioning to spring time hours in preparation for the end of the season.  We are issuing forecasts 4 days/wk on Sat, Sun, Tue, Thur. The final forecast will be on April 28th.  You can check out springtime tips on the final Summit Summary  HERE.  

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Tue, April 17th, 2018
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
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
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Wet Loose
    Wet Loose
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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

Today’s weather is forecast to be a little bit of everything. It looks to start out sunny and then transition to rain and snow showers with increasing East winds. Crusts that formed overnight may or may not soften in the sunshine by late afternoon. If the snow does become soft (and especially if it starts to rain after) the potential for wet loose activity at lower elevations will increase. Observations over the weekend found the weakest wet snow conditions below 2500’ on very steep East to South aspects. There is more potential for wet snow to entrain a larger avalanche in this elevation band if they warm up enough. Don’t let this catch you off guard if you start out in the upper elevations and the snow quickly changes as you descend. Pay attention to surface crusts as they break down and become moist. When the snow becomes wet and ‘mushy’ and your skis or snowmachine track start trenching into wet snow, it’s time to find supportable surfaces. Even a small wet avalanche could be hard to manage especially in a terrain trap. 

Cornices: Daily warming and sunnier weather can make cornices more unstable. As always, give cornices plenty of space and limit exposure underneath them.

Recent cornice triggered slab avalanche above Skookum and old wet loose avalanches. 

Additional Concern
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

Triggering a persistent slab 1-2’ deep is becoming less likely with time. Old weak snow (facets) buried within the top 2’ of the snowpack has been found in the upper elevations over the last few weeks. Northerly aspects above 3000’ with dry snow may harbor this set up. So far there have been no reports of any avalanche activity on these shaded slopes following last week’s storm. However, the periphery of our forecast zone is more suspect, Crow Pass area and Johnson Pass to Summit Lake, where a thinner (weaker) snowpack remains. Before committing to steeper slopes in the upper elevations, take a moment to evaluate the terrain for consequences should a slab release.  

Weather
Tue, April 17th, 2018

Yesterday was partly sunny with high clouds moving in. Temperatures were in the 30Fs and 40Fs. Winds were from the East 5-15 mph with gusts into the 20s. Overnight temperatures were in the low 30Fs to mid 20Fs.  

Today is forecast to be partly to mostly cloudy. There is chance of rain and snow showers in the late afternoon. Easterly winds will increase with gusts into the 30s and 40s. Temperatures will be in the 20Fs to low 40Fs depending on elevation. Tonight rain and snow showers are likely but not much accumulation is expected. Rain/snowline is forecast to be around 1000′.

Tomorrow the rain and snow showers continue and East winds will remain elevated. Temperatures will be in the high 20Fs to low 40Fs.The wet weather and Southeast flow continue into Thursday. There is another low moving into the Gulf this weekend, which could bring more rain to the area.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 36    0 0   65  
Summit Lake (1400′)  30      0 0    23    
Alyeska Mid (1700′) 35     0   0   60  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  25  ENE 9   20  
Seattle Ridge (2400′)  31  ESE  10 25  
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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.