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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, January 22nd, 2018 - 7:00AM
Expires
Tue, January 23rd, 2018 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

There remains a  MODERATE  avalanche danger on all aspects above 2,500′ for triggering a very large slab avalanche between 3 and 8+’ thick. These deep slab avalanches are more likely to be found at the higher elevations, above 3,000′. They are difficult to trigger, but if so could have high consequences. Additionally, loose snow sluffs should be expected on steep slopes and be aware of cornice falls along ridgelines. There is a  LOW  danger below 2,500′ where triggering a slab avalanche is unlikely but sluffs are possible.

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Mon, January 22nd, 2018
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
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
Low (1)
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

Last night a cold moist air mass brought a several inch refresh to the Girdwood and Portage Valleys (4-6″), yet only an inch or two for Turnagain Pass. Water weight was only in the .25 – .1″ range, but most of us will take what we can get to cover the crusts at the lower elevations! With that said, until we see more weather, snow, rain, etc, our avalanche problems on the surface remain on the small side (see below) and our main concern still lies with a much larger, but stubborn avalanche problem.

Deep persistent slab avalanches remain our primary concern, which exist in the high elevation terrain above 3,000′. On these upper elevation slopes, there is a dense hard slab sitting on a variety of weak layers in the mid pack (buried surface hoar) and old November facets near the ground. Triggering a deep slab is becoming more and more difficult, but still possible. The most likely trigger spots are thin areas in the snow cover, often near rocks, or where the slope rolls over. High peaks, that see wind, can also be thinner and more likely to find a deep slab.

Again, here are a few points that keep sending home with our current snowpack set up:

–  We have a ‘low probability, high consequence’ situation at the upper elevations for deep slab avalanches
–  
Obvious signs of instability are not likely to been seen before a deep slab is triggered (such as whumpfing and cracking)
–  Remote triggering is possible 
–  Last, this issue can simply be avoided by sticking to terrain below 3000’ (which is a good portion of terrain at Turnagain) or choosing low-consequence terrain in the alpine

Photos of old avalanche debris from the Seattle Headwall area. Last week’s warm storm initiated very large avalanches on many slopes, yet many still remain intact and did not avalanche. 

  

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

Ridgetop winds bumped up slightly last night into the 10-15mph range from a generally Easterly direction. This isn’t much for wind, but with such loose surface snow existing right now, it could be enough to form shallow wind slabs along ridgelines. Watch for recent wind texturing on the snow surface and feel for stiffer wind packed snow over softer snow or a crust. If you happen to find a fresh wind slab, expect it to be quite touchy.

Additional Concern
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

Again, the loose surface snow is quick to sluff and has been running far on steep slopes. Hence, watch your sluff on the steeper slopes. Any additional new snow from overnight will add to the volume of these and could catch a person by surprise. 

Photo of loose surface snow (near surface facets) over a stout crust in the mid-elevations. Another crop of surface hoar (on the top of the snow in photo below) grew last weekend and now sits under the little bit of new snow from last night. 


Weather
Mon, January 22nd, 2018

Mostly cloudy skies filled the area yesterday with a few snow flurries region wide. Snowfall increased overnight and the Girdwood and Portage Valley areas picked up 4-6″ at the mid-upper elevations while Turnagain Pass looks to have seen only around an inch. Ridgetop winds from the East, Northeast bumped up slightly overnight, blowing 10-15mph with gusts into the 20’smph. Temperatures have warmed at the high elevations into the low 20’sF, while valley bottoms remain around 10-15F this morning.  

Today, mostly cloudy skies are expected with a snow flurry or two (little to no accumulation). Ridgetop winds are slated to remain light from an Easterly direction, 5-10mph. Temperatures should warm to the mid-upper 20’sF in valley bottoms and remain near 20F along ridgetops.  

For tonigh night into Tuesday morning there is another chance for a few inches of snow to sea level, possibly up to 6″ in favored areas. Winds look to remain light to moderate with this pulse of moisture and temperatures look to remain in the teens to 20’sF. Stay tuned.

*Seattle Ridge anemometer is rimed over and not able to collect wind data.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 11   1   0.1   54  
Summit Lake (1400′) 7   0   0   15  
Alyeska Mid (1700′) 12   4   0.23   47  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19   NE   7   21  
Seattle Ridge (2400′) 15   *n/a   *n/a   *n/a  
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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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