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Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, March 15th, 2014 - 7:00AM
Expires
Sun, March 16th, 2014 - 7:00AM
Forecaster
Kevin Wright
The Bottom Line

Since Monday Turnagain Pass has another ~50 inches of snow on the ground.   This has come through 2 storms €“ one that started Monday, the other that just tapered off late last night.    

This is a huge additional burden for the snowpack to hold.  The kicker is that this new snow is sitting on a persistent weak layer above the February melt/freeze crust.  Avalanche danger will be  CONSIDERABLE  at all elevations.

 Partly cloudy skies and a fresh blanket of snow will make for an enticing combination today.   This is not an “anything goes” kind of day.  Conservative terrain choices will be essential today.

 Avalanches may be difficult to trigger, but if you get something to move it’s going to be big and dangerous.

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Sat, March 15th, 2014
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
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
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.
More info at Avalanche.org

It’s been snowing – a lot!  Anchorage got a significant dump last night.  That snow extended to Girdwood and beyond.  This is the kind of maritime storm pattern that we are famous for, and we’ve been missing during this drought winter.  

The storm snow problem is least stable during the active part of the storm, and tends to stabilize quickly over time.  The big message today is that we got a LOT of snow and it will need time to settle out, bond, and stabilize.  We are still within the 24 hour window since active storming, and still within the window of high probability to trigger avalanches in the new storm layers.  

Storms also create wind slabs and build cornices.  Cornices are likely to be bigger and less stable than they were last weeekend.

Time will make these storm layers stable, but today is not the day to test them in big and dangerous terrain.  

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
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.
More info at Avalanche.org

Underneath all the fresh snow from the last 5 days is the prominent crust layer that formed in February.  Just above this crust is a weak layer of faceted snow mixed with buried surface hoar.  

We did some snow pit testing yesterday.  Results indicated the most concerning weak layer (above the Feb. crust) is difficult to initiate, but propagation potential is high.  The triggering is difficult because our slab layer (40-50 inches of new snow) is thick and strong.  This information tells us that avalanches may be difficult to trigger, but when they do the resulting avalanche can be large and deep.  

This kind of deep slab problem is most likely to be triggered from an area of shallower snow.  Wind loading patterns during the storm caused scoured ridges which quickly transition to deeply loaded slopes on the downwind side.  A skier or snowmachiner is more likely to trigger this problem near the scoured ridge than far into the deep pocket.  Once initiated, it could propagate across into the deeper snow.

Larger triggers are also more likely to initiate the deep slab.  Snowmachines have the disadvantage here with 600+ pounds of sled and rider weight impacting the slope.  

Weather
Sat, March 15th, 2014

This has been a great week for snowfall.  Turnagain Pass more than doubled the total snow on the ground from 42 inches on Sunday to 88 inches last night.  Total new snow water equivalent is 5.9 inches.  Wind during the storm was predominately from the east on Sunburst.  Rain did reach up above 1000 feet at times during the storms, but the snow dried out at the tail end of the storm all the way to sea level.  

Last night we got a final shot of snow during a cooling temperature trend.  This last bit of the storm was widespread from Anchorage to eastern Turnagain Arm.  

A chance of snow continues today, with a couple more inches possible.  Decreasing clouds through the day may allow the sun to poke through at times.  Temperatures should be cooler, in the low 20s.  Wind will be light from the south.  

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Riding Areas
Updated Mon, October 26th, 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
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.