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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, March 9th, 2019 - 7:00AM
Expires
Sun, March 10th, 2019 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is CONSIDERABLE  this morning due to 1-2 feet of new snow in the past 24-hours. The danger is expected to rise to HIGH this evening as another round of snow and wind moves in. Human triggered slab avalanches, up to 2+ feet thick, will be likely. Natural avalanches will be possible. The new snow is falling on a very weak base and expected to slide easily on steep slopes.  We are entering spring break with a dangerous avalanche situation and restraint will be required as travel in avalanche terrain is not recommended.  

PORTAGE VALLEY:  Natural avalanches are possible today that could send debris to valley floors. Areas with steep slopes and avalanche terrain above you, such as the Byron Glacier Trail, should be avoided.

SUMMIT LAKE:   Despite little new snow, this area has a very shallow snowpack with multiple weak layers. Strong winds and the potential for a few inches of new snow today could overload buried weak layers, producing an unexpected slab avalanche. Caution is advised if heading to this area.

LOST LAKE:    Dangerous avalanche conditions are expected in the Lost Lake and Seward regions as well due to 1-2 feet of new snow and strong winds.  

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Sat, March 9th, 2019
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
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
Considerable (3)
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
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

It’s a simple equation:  new snow falling on a slippery surface + wind loading = easily triggered avalanches.

Heads up for anyone headed out today. Storm snow avalanches are expected to be easily triggered. These will be in the form of wind slabs on wind loaded slopes, storm slabs in areas out of the wind, cornice falls and new snow sluffs. The size of the avalanche will depend on the amount of new snow and wind loading. In the Girdwood Valley slabs could be up to 3′ thick on wind loaded slopes. In the Turnagain Pass area, slabs could be up to 2′ thick. Come tomorrow, add another 10-20″ to the thickness of these slabs. 

Although hidden from view, under the storm snow is the old surface, which is a combination of sun and wind crusts, facets and surface hoar. Not only will this old surface inhibit bonding with the new snow, it may also allow slabs to propagate wider than expected. Remotely triggered avalanches are also possible, meaning triggering a slide from the ridge or the bottom of a slope. With another round of snow and wind slated to hit later today, pushing the danger to HIGH, now is the time for us to keep out of avalanche terrain and let the mountains do their thing. 

Estimated storm totals (mid-upper elevations) beginning Thursday ending Saturday 6am:

  • Turnagain Pass:  10″ – 16″ snow (1″ water)
  • Girdwood Valley:  16 – 24″ snow (1.5 – 2.3″ water)
  • Summit Lake:  1-2″ snow (0 – 0.1 water)
  • Bear Valley (Portage):  20 – 30″ snow (2 – 2.5″ water)
  • Seward area:  12″ – 20″ snow (1-1.5″ water)

 Rain has been falling below 1,000′ and expected to continue today. This whas saturated the low elevations and wet sluffs will be possible. 

Storm slab avalanche in the Tincan Trees from yesterday. Roughly 6 more inches of snow has fallen with more on the way, which will create much larger slabs for today. Photo: Allen Dahl.

 

The photo above shows the 6-8″ of new snow from yesterday sliding easily on the old sun crust that was the surface a few days ago. (Photo: Allen Dahl)

Weather
Sat, March 9th, 2019

Yesterday:   Light to heavy snowfall was over the region as the second storm front passed through. Rain fell up to 500′ and in some areas up to 1,000′. Snowfall amounts across the region varied greatly from only a trace in the Summit Lake area to over 2 feet in the upper Girdwood and Portage Valleys. Turnagain Pass has seen around a foot of new snow. Ridgetop winds over the past 24-hours have been blowing 20-30mph from the east with stronger gusts. Temperatures have been steady in the low to mid 20’sF along ridgelines and in the mid 30’sF near sea level.

Today:   A brief break between storms is expected this morning with the third wave of precipitation moving in midday and peaking late tonight. An additional 3-6″ of snow is expected to fall today with 10-14″ tonight. The snow/rain line should creep up to 1,500′ in areas and therefore, rain will be falling at the low elevations. Ridgetop winds are forecast to remain easterly in the 20-30mph range with gusts up to 50mph. Temperatures may reach the upper 40F at sea level, 32 at the mid elevations and the mid 20’sF along ridgelines.

Tomorrow:    Stormy weather will continue Sunday and into Monday with an additional 6-12″ of snow at the mid and upper elevations. Cooler air looks to be entrained on Monday, which will lower the rain line and snow could fall near sea level. Another small break in storms may occur Tuesday before another round of precipitation hits. Stay tuned!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31   10   0.8 63  
Summit Lake (1400′) 33   trace    0 26  
Alyeska Mid (1700′) 30   14   1.05   67  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21   NE   29   57  
Seattle Ridge (2400′) 27   SE   14   27  
Observations
Recent Observations for Turnagain Pass
Date Region Location
12/08/19 Turnagain Avalanche: Tincan
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12/04/19 Turnagain Observation: Sunburst
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12/01/19 Turnagain Observation: Tincan, All elevations
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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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