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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, March 17th, 2019 - 7:00AM
Expires
Mon, March 18th, 2019 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

Another storm hitting the region today will keep the avalanche danger  HIGH. Large and dangerous avalanches continue to release naturally as rain, snow and wind impact the area. Avalanches releasing in the high elevations have been sending debris to valley floors, which is expected again today.  Travel in avalanche terrain is not recommended.  Avoid slopes 30 degrees or steeper, including runout zones.  


SUMMIT LAKE (& INTERIOR EASTERN KENAI MTS)
 – Although precipitation rates should be less today in the interior Kenai, large to very large human triggered avalanches remain very likely. Up to 30″ of snow has fallen onto a very weak base over the past few days.  Travel in avalanche terrain is not recommended in these zones.

SEWARD/LOST LAKE  –  Large and dangerous natural avalanches  have been observed in this area. Continued rain, wind and snow at the high elevations will keep the avalanche danger elevated and  travel in avalanche terrain is not recommended.  

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Sun, March 17th, 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

Temperatures are rising as yet another storm moves into the region. As of this morning, rain is falling up to 1,500′ with wet snow above this. The rain line is expected to rise as high as 2,500′ in places and drop around an inch of water over the day. The higher elevations are expected to see up to a foot of new snow. This will give the mountains another shock to the system as rain-on-snow could induce natural wet avalanches on steep slopes below 2,500′. Snowfall and strong winds at the upper elevations will continue to load slopes and natural dry snow avalanches are expected. As storm after storm keeps adding more snow to these high elevations, the avalanches are becoming larger, sending debris further and nothing to mess with. There is anywhere from 5-8+ feet of settled storm snow from over the past week and with more snow on the way, it is another day to leave the mountains to themselves.

With obscured skies limiting visibility, it’s difficult to gauge the extent of naturally occurring avalanches over the past week. However, all it takes is a look at the bottom of avalanche paths and you’ll find most are filled with debris. Check out the video below, courtesy of Dwayne Clevenger, that shows debris covering the trail into Lynx Creek drainage. The message here is, avalanche terrain is not only on slopes over 30 degrees, it also includes runout zones (flat areas under steep slopes). Other trails, such as Byron Glacier trail or Johnson Pass trail, run through avalanche terrain and are examples of areas to be avoided during stormy weather.  


 
Big thanks to Dwayne Clevenger for this video of avalanche debris covering the Lynx Ck trail on Mar 16, link HERE.

 


5′ settled storm snow video link HERE.

 


Around 5 feet of snow has piled up since March 8th. The snowpack has almost doubled since then, yet is settling fast with the rain and warm temperatures. 

 

Storm Totals (Wed 6am – Sun 6am): 

  • Turnagain Pass 1800′:  25″ — 4.9″ SWE  (As seen above, 5′ of settled storm snow was found at 2,100′)
  • Girdwood-Alyeska Midway 1700′: ~30″ — 4.3″ SWE
  • Summit Lake 1400′: ~16″ — 1.6″ SWE
  • Portage Valley 95′: ~6-8+ ft snow in upper elevations — 9.25″ rain 
Weather
Sun, March 17th, 2019

Yesterday:   Another warm stormy day was over the area. Skies were mostly obscured with light rain falling below 800 – 1,100′ and moist snow above this. Roughly 1″ of rain fell in Girdwood while just over 1/2″ of rain fell on Turnagain Pass; Portage Valley was the winner with 3″ of rain. Snow amounts can be equated to 12-18″ at the higher elevations in Girdwood and 5-8″ at the higher elevations on Turnagain. Ridgetop winds have been easterly in the 30-40mph range with gusts up to 70mph. Temperatures reached the mid 30’s F at 1,000′ and the upper 20’s F along the ridgelines.  

Today:   Another wave of precipitation and wind is hitting us today. This storm front is warmer and 1″ of rain is forecast to fall up to 2,500′ with a foot of moist snow in the Alpine. Ridgetop winds will rise into the 40-50’s mph with stronger gusts from the east. Temperatures will continue to climb, ridgelines could see 32F while 1,000′ elevations, along the road at Turnagain Pass, may push to 40F.  

Tomorrow:   This storm will be slowly moving out tomorrow and light precipitation is expected with decreasing easterly ridgetop winds. Skies may clear enough to see the higher elevations. Weather models are showing another warm system impacting the region Tuesday night into Wednesday with continued rain/snow and wind.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33   3   0.6   98  
Summit Lake (1400′) 36   0   0.1   34  
Alyeska Mid (1700′) 33   2   1.2    87

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25   NE   34   71  
Seattle Ridge (2400′) 30   *N/A   *N/A     *N/A    
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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.