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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, January 1st, 2020 - 7:00AM
Expires
Thu, January 2nd, 2020 - 7:00AM
Forecaster
Ryan Van Luit
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′ where it’s likely for a human to trigger a large and dangerous avalanche.  Wind slabs and storm slabs up to 3′ thick are our primary concern and could be triggered on the slope itself or from below, above or near the slope.  Cornices have grown and remain a hazard.  Very conservative terrain management and decision making is advised.

UPDATE:  The lower elevation band, below 1,000′, the avalanche danger is CONSIDERABLE for 12-18″ of new snow that fell last night. Winds slabs in areas with wind effect and sluffing should be expected.

Special Announcements
Seward Highway Road Closures:  The Seward Highway is closed early this morning. Please keeps tabs on road conditions and closures at 511.alask.gov.
 
Chugach State Park area:  Dangerous avalanche conditions are expected in areas seeing new snow and wind.
Wed, January 1st, 2020
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Recent Avalanches

Yesterdays rain and rapid warming contributed to numerous large natural avalanches being reported in upper Girdwood and Crow Creek Valley, through the Portage Valley and near Summit lake.  There was also one skier triggered slab avalanche on Tincan above treeline on a small(ish) rollover. This slab was 2 feet deep and 100 feet wide running 150 feet down. No one was caught.

With limited visibility yesterday, it’s unknown but suspected that many of the natural avalanches initiated in both alpine and treeline elevations, with debris running to valley bottoms in some cases.

The Five Sisters slide path in Portage Valley

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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
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

Happy New Year from all of us at the CNFAIC!

Yesterday the advisory area experienced a rapid warming event in conjunction with rain up to 2200′.  This additional load tipped the balance on many steep slopes causing numerous large avalanches.  Last night, winds picked up and rain shifted to snow as the temperatures suddenly dropped into the teens and snow fell to sea level. Over the past 24-hours the Alpine has seen 15 – 25″+ of new snow in Girdwood Valley and Turnagain Pass. Summit Lake is estimated at 8-10″ of snow in the Alpine while Portage Valley was the big winner with over 4′ of snow near Portage Pass.

Today, temperatures will move toward the single digits and winds should blow from 15-25mph. This may contribute to the high wind effect over the past day and continue to actively load slopes on the lee of ridges and gullies. The new load of snow from the past few storms sits on top of weak snow 2-3′ deep along with a documented weak layer of buried surface hoar from Solstice.  Although we have cooling temperatures, the snowpack is still adjusting to the load and large slab avalanches are likely to be triggered. The snowpack set-up such that remote triggering a large slab is possible. This means triggering an avalanche from below, above or adjacent to the slope.

Very cautious route-finding is essential today. There were several observers who experienced long shooting cracks and large wumpfing yesterday and this will likely be the case again today.  These are clear indicators for us to reconsider our route and plan. These and other red flags should be up front in our minds:

  • Signs of recent avalanches
  • Whumfing in the snow under you (collapsing of the snowpack)
  • Shooting cracks in the snow around you

Cornices:  Strong winds and new snow have further developed the cornices throughout the region. With such varying layers and densities within the snow and wind cycles, it’s prudent to give cornices extra caution- limit your time beneath them, and give them a wide margin.

Weather
Wed, January 1st, 2020

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

Yesterday: Cloudy skies prevailed yesterday as warm storm moved through. Rain fell into the evening up to 2,200′ before the temperatures dropped into the teens F overnight.  Snow accumulation from 10-20″ near 1000′ and an estimated 15-25″ or more in the Alpine.  Temperatures ranged from 40°Fs at sea level to mid 20°Fs at ridgetops. Winds were from the east at 20 to 40 mph, gusting to 60mph.

Today: Cloudy skies today with a chance for some partial clearing as the storm moves out. Temperatures will continue to drop toward a low tonight of  6°F, with snow accumulations of 1-3″ near 1000′.   Temperatures will likely range from 20°Fs at sea level to single digits °Fs at ridgetops. Winds will be from the southeast at 15 to 25 mph, gusts possible to 40mph.

Tomorrow: Cloudy with a chance of snow flurries all day and into the evening.  Temperatures will remain in the teens to a low near 5°F and winds will be out of the southeast at 5 to 10 mph.

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 12 1 45
Summit Lake (1400′) 33 3 0.7 14
Alyeska Mid (1700′) 33 15 1.7 38

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 27 ENE 24 57
Seattle Ridge (2400′) 29 N/A N/A N/A
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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.