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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, April 11th, 2018 - 7:00AM
Expires
Thu, April 12th, 2018 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

Above freezing temperatures and rain showers will keep the danger at  CONSIDERABLE today. Human triggered wet snow avalanches are likely and naturals are possible. In the Alpine triggering a slab avalanche 1-2′ thick remains possible on Northerly aspects where drier snow exists. Give cornices a wide berth.

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Wed, April 11th, 2018
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
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
Considerable (3)
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
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

Yesterday saw heavier rain in the early morning then rain showers on and off throughout the day. Portage picked up over an inch of rain. Temperatures were above freezing to around 3500′. Observers reported snow becoming progressively more saturated especially below 2000′. Skies cleared briefly last night and there was a superficial freeze. However, today a bit more rain is in the forecast, we may see some afternoon clearing with direct sun and the temperatures remain warm. All these factors are continuing to make triggering a wet loose avalanche likely and naturals remain possible. There were a number of natural wet loose avalanches observed yesterday with the largest occurring on the west face of Pyramid mid morning. The snowpack could continue to get more saturated throughout the day. If you do decide to recreate today pay attention to the depth you are sinking in and get off the slope if the snow is over your boot tops or your machine is trenching in. Watch for roller balls.  Expect loose snow moving to entrain more as moves downhill. Any fresh snow in the Alpine may be especially reactive on solar aspects if the sun comes out today. 

Wet slab avalanches:  We have not seen any wet slab avalanche activity yet, but it’s not out of the question that a wet loose slide (or the weight of a skier or snowachiner) could trigger a wet slab today as water penetrates to lower layers. 

Natural wet loose avalanche on Pyramid

Wet loose avalanches on Magnum

Avalanche Problem 2
  • 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

Above the rain line triggering a slab avalanche 1-2′ thick on Northerly shaded aspects is still possible. Overall we have seen that the snow from last week has been bonding but haven’t forgotten that there is a weak layer under the old storm slab.  The slab/facet combo remains suspect and may be more tender in the Alpine with the additional few inches of heavy snow from yesterday. Wind loading may also add stress, as the ridgetop winds remained strong yesterday and continue today. 

Additional Concern
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

It’s that time of year where the snowpack is warming up and cornices will begin to break. Give cornices a wide berth.

Weather
Wed, April 11th, 2018

Yesterday was partly to mostly cloudy with heavier rain falling in the early morning and localized rain showers on and off throughout the day. Over an inch of rain fell in Portage Valley. Temperatures were in the 30Fs to 40Fs. Winds were Easterly 15-25 mph with gusts into the 40s. Overnight there was brief period of clearing. Temperatures remained above freezing to around 3500′. Sunburst (3812′) hit 32F this morning at 5 am. Easterly winds decreased overnight and are picking up again this morning.  

Today is forecast to be mostly to partly cloudy with rain showers. Winds will be easterly 15-25 mph with gusts into the 40s. Temperatures will be in the 30Fs and 40Fs. Tonight temperatures will cool down a bit as colder air moves into the region.  

The weather for the next couple of day looks to be a mix of sun and clouds, rain and snow showers and variable temperatures. If the cooler air lines up with some clearer skies at night we could get more of a freeze. Sunshine is in the forecast for the weekend.    

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  38  0 0.2 73  
Summit Lake (1400′)  36   0    0.1  28    
Alyeska Mid (1700′)  37  0  0.1  69    

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  28  ENE  20 45  
Seattle Ridge (2400′)  33  ESE  13  27    
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Riding Areas
Updated Mon, December 02nd, 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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