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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, March 20th, 2018 - 7:00AM
Expires
Wed, March 21st, 2018 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is CONSIDERABLE above 2500′. Strong winds today could trigger natural wind slabs in the Alpine.  Triggering a large, destructive slab avalanche 2-4+ feet thick is possible on all aspects above 1000′. Watch for tender wind slabs along ridgelines and avoid cornices. Pay attention to afternoon warming. Evaluate snow and terrain carefully.  

Below 1000′ the danger is LOW. Wet snow is now freezing into hard crusts.  

Check out the most recent  Summit snowpack and avalanche summary  if you are headed South of Turnagain Pass.

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Tue, March 20th, 2018
Alpine
Above 2,500'
Considerable (3)
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
Considerable (3)
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
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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’s weather was all over the place. Snow and rain in the morning and then sunshine, strong winds and cooler air moving into the region. There were a few dry loose avalanches and small wind slabs observed. Today continued wind loading may trigger natural wind slabs and/or add stress to the snowpack. It is also important to keep in mind that triggering a deep slab avalanche 2-4+ feet thick remains possible. On Saturday snowmachiner triggered slab in Main Bowl of Seattle Ridge, the slope had tracks on it from the day before and was remotely triggered from below. Remember that over the past week many large human triggered avalanches and/or natural avalanches have released from Girdwood to Lost Lake. Some of these avalanches have been remotely triggered and some with skier/snowmachiners on the slope.  Widespread buried surface hoar and facets have been well documented at all elevations under a thick, connected slab and finding the wrong spot could be deadly. 

*With a deep slab problem it is important to remember no signs of instability may be present before a slope releases. It may be the 10th person onto the slope that finds the trigger point and slopes may be triggered remotely. It is crucial to visualize the consequences if the slope does slide. Are there terrain traps below?  Bigger slope = Bigger avalanche. Thin spots near rocks and along ridgelines are likely areas to find the trigger point. 

Avalanche triggered on Sunburst last week illustrates the trigger point that had a shallower snowpack near a rocky ridge. 

Deep slab structure: 3 feet of snow over a buried weak layer.

 

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

Strong Northwest winds blew 25-35 mph yesterday and gusted into the 70s on Seattle Ridge. Winds are forecast to remain elevated today and ramp up even more this evening into tomorrow. Be aware of wind slabs on a variety of aspects due to unusual wind loading patterns and cross loading. Smooth supportable surfaces where the snow is hollow sounding are suspect, especially if the slope is unsupported. Look for cracking and identify terrain features with a pillow-shaped look where triggering a wind slab could break above you. A fresh wind slab could step down to older snow in the snowpack and create a much deeper and more dangerous avalanche. 

Wind loading yesterday. 

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

Cornices are large and looming and wind loading can add stress. Give these an extra wide berth and limit exposure underneath them.  A cornice fall could trigger an avalanche on a slope below.

 

Weather
Tue, March 20th, 2018

Yesterday started out with snow  and a little rain (at lower elevations) and then the wind started to blow from the Northwest. The skies cleared and the sun came out. Temperatures were in the mid 20Fs to mid 30Fs. The NW winds were blowing 25-35 mph with gusts into the 70s. Overnight temperatures dropped into the low 30Fs and low 20Fs/high teens. Winds continued from the NW gusting into the 30s and 40s.  

Today will be partly cloudy with slight chance of snow showers. Winds will remain elevated from the NW gusting into 50s. Temperatures will be in the 20Fs to low 30Fs. Tonight skies will be clear and temperatures drop into the teens and single digits. The NW winds continue gusting into the 40s.  

Wednesday is forecast to be clear and sunny. The winds may be even stronger.   High pressure continues until the weekend and then there looks to be shift back to an active weather pattern.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  30  2 0.2    83
Summit Lake (1400′)   25    2 0.1  33
Alyeska Mid (1700′)  28  3 0.28    78

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  17 NW   10   47  
Seattle Ridge (2400′)  24  WNW  30   70  
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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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