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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, March 16th, 2019 - 7:00AM
Expires
Sun, March 17th, 2019 - 7:00AM
Forecaster
Graham Predeger
The Bottom Line

The avalanche danger is  HIGH  for a fourth consecutive day given the continuation of a series of warm, wet and windy storms depositing heavy snow and rain in rapid succession in the Turnagain Pass area.    Travel in avalanche terrain is not recommended again today.    Avoid slopes 30 degrees or steeper, including runout zones.  

SUMMIT LAKE (& INTERIOR EASTERN KENAI MTS)   €“ Areas around Summit Lake have effectively doubled their seasonal snowpack in the past week and dropped up to a 30 € storm slab on a very weak base of facets.   Large to very large human triggered avalanches are very likely again today.  Travel in avalanche terrain is NOT recommended in these zones.

SEWARD/LOST LAKE   €“ Coastal areas such as Seward have seen big precip numbers this week, much in the form of rain.   Natural avalanches large enough to bury, injure or kill a person have been observed. Again,  travel in avalanche terrain is NOT recommended.

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Sat, March 16th, 2019
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
High (4)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
High (4)
Below Treeline
Below 1,000'
Avalanche risk
High (4)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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

Each low-pressure event impacting our area over the past week seems to be bringing slightly warmer temperatures than the last; today will be no exception.  As temperatures increase, the rain/ snow line may reach as high as 2,000’ as this next bout of weather impacts the eastern Kenai Peninsula this weekend.  What does this mean for avalanche activity today?  It means that rain on snow may initiate natural avalanches in the treeline elevations where we’ve seen mostly snow for the past 3+ days.  Any avalanches today will be large and un-survivable as storm slabs alone are 2-3’ deep.  Add winds to that or the potential for an avalanche to step down into weaker layers deeper in the snowpack and we’re flirting with the potential for 5-6’+ deep avalanches.

Though observations and info from the alpine (above) 2,500’ have been minimal since Tuesday, an additional 8-16″ of snow forecated and strong easterly winds over known weak layers and crusts create a serious concern for large and destructive avalanches today.  In channeled terrain, debris was running to the valley floor and all the way to sea level in some cases yesterday.  Today the message is simple – Avoid all avalanche terrain, this includes slopes steeper than 30 degrees and all runout zones. 

South of Turnagain Pass: A brief weather window on Thursday allowed observers to view a plethora of natural avalanches that ran mid-storm.  Given a shallower snowpack in these areas, this week’s load is proving generous enough to tip the stress vs. strength balance south of the core Turnagain Pass area.  Suspect areas include Johnson Pass, Lynx Creek and Summit Lake.  

Debris in channelled terrain in the bottom of east facing terrain at the base of Twin Peaks. Just south of Turnagain Pass.  Photo: 3/14.

Storm Totals (Wed 6am – Sat 6am): 

  • Turnagain Pass 1800’:  29” (settled snow) — 4.3” SWE
  • Girdwood-Alyeska Midway 1700’: ~30” — 3.14” SWE
  • Summit Lake 1400’: ~19” — 1.5” SWE
  • Portage Valley 95’: ~5-6 ft snow in upper elevations — 6.25” rain at reporting station
Weather
Sat, March 16th, 2019

Yesterday:  Temperatures in the mid to upper 30’s kept rain the dominant precip type below about ~700′.   Turnagain Pass (1,880′) only saw ~3 € of wet, heavy snow (.9 € water) as accumulation was barely keeping up with settlement rates.   Ridgetop winds were sustained from the east in the mid 30’s €“ 40mph with gusts into the low 70’s at Sunburst.

Today:  Temperatures continue to climb into the high 30’s at 1,000′ with the rain/ snow line anticipated to be in the 1,800′ €“ 2,000′ range.   On average we can expect another ~1 € of water though areas such as Portage and Girdwood could see more.   In the alpine this translates to another 8-16 € of snow.  

Tomorrow: The active weather pattern continues as yet another surface low moves into southcentral AK.   Expect more rain in the lower elevations, moderate to strong southeasterly winds and ample snow/ whiteout in the alpine.   Rain/ snow line looks to be in the 1,800-2,400′ range.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  32  3  .9 102  
Summit Lake (1400′)  35  0 .2   37  
Alyeska Mid (1700′) 32   0   .89   89  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  23  ENE  42 88  
Seattle Ridge (2400′)  28 n/a *  n/a*  n/a*

*Seattle Ridge weather station is not reporting reliable wind data at this time.

Observations
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Riding Areas
Updated Fri, May 01st, 2020

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
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Closed as of May 1. Thanks for a fun, safe season!
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
Closed
Resurrection Pass Trail
Closed
Snug Harbor
Closed
South Fork Snow River Corridor
Closed
Summit Lake
Closed

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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.