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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
Sun, January 13th, 2013 - 7:00AM
Expires
Mon, January 14th, 2013 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

A substantial rise in temperature along with precipitation at all elevations will increase the avalanche danger to HIGH today.  Rain on snow below 3,000ft and heavy wet snow above will destabilize the snowpack as a whole. Natural avalanches are likely and human triggered avalanches are very likely. The potential exists for very large, full depth avalanches to release. These have the ability to run all the way to the flats and deposit significant amounts of debris. Travel in any type of avalanche terrain is not recommended.

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Sun, January 13th, 2013
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
  • 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

Once again, our primary concern deals with deep slab avalanches. These are failing in the weak layers at the bottom of the snowpack and can bring down large, dangerous and far running slides. It has been 4 days since the last deep slab was triggered but today the likelihood will go up with the rapid rise in temperature and the addition of rain and/or wet snow.

The precipitation amounts for this storm are not exceptional for this year around Turnagain Pass but the warm temperatures are. Most of our start zones lie in the 2,000 – 4,000’ elevation band and it is exactly this band which has harbored colder, dry snow so far this year and will get a shock as it warms up today. The slab that overlies our weak October and November snow is essentially one cohesive layer 4-8′ thick. It is a complex phenomenon as to why rapid warming destabilizes a dry snowpack. Essentially, the properties of the slab (our 4-8′ cohesive layer) change which increases the stress on the underlying weak layers (our October and November facets). There is a good chance that there are several slopes out there teetering on the balance and that balance may be tipped today.

Avalanche Problem 2
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

Rain on snow near 3000ft and below will give our mid-elevation snowpack a jolt and decrease stability rapidly. Though the lower elevations (below 1,000ft) have seen their fair share of rain it is the next 2,000ft above this that is the biggest problem. As many old-timers say “rain on dry snow is never a good thing”. These wet avalanches can initiate in the top foot or two of the pack where the rain is being absorbed and become quite large on their descent by entraining additional snow in its path. They also have the ability to “step down” and trigger a deep slab avalanche, in which case will mostly likely be quite large. Wet snow avalanches contain very dense snow that is typically slow moving but they also mow down and destroy most things in their path.

 

Weather
Sun, January 13th, 2013

Very warm air is on our doorstep as tropical moisture is being pulled up into our neck of the woods. Anchorage is already in the thick of it but Turnagain Pass is trailing a bit behind. We should see temperatures steadily climb throughout the day and top out near 32F at 4,000′ by this afternoon. The rain/snow line is currently around 1,500′ but will rise to around 3,000′. There has been 0.9 € of water equivalent (7 € of high density snow) in the past 24 hours as of 6am on Turnagain Pass and quite a bit more, 2-2.5 € of water equivalent (~18 € heavy snow), in the Girdwood Valley. Ridgetop winds are out of the SE averaging 25mph and gusting up to 50mph.

We should see around another 1 € of water through the day with most of it falling as rain and very wet snow near 3,000′. Wind will remain SE and in the 20-30mph range with higher gusts on the ridges. Temperatures at treeline will rise to the upper 30’s. F. The rain and wet snow will continue overnight and taper off tomorrow with cooling temperatures.

Pictured below – the “fire hose” of tropical moisture pointed right at southern AK.   (current on page refresh of GOES IR image)


Fitz will issue the next advisory tomorrow morning, January 14th.

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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
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Closed
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Skookum Drainage
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Turnagain Pass
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Closed as of May 1. Thanks for a fun, safe season!
Twentymile
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Carter Lake
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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.