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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Sunday, January 13th 2013
Created: Jan 13th 6:51 am
4 High Alpine / Above 2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
4 High Treeline / 1,000'-2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
4 High Below Treeline / Below 1,000' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
 Show the Complete North American Avalanche Danger Scale
Special Announcement

The AK DOT will be conducting avalanche hazard reduction work today on the Seward Highway between Bird and Portage (MP99-83). Motorists should expect intermittent closures and delays of up to 45 minutes between 9:00AM and 2:00PM. Updates can be founds at 511.alaska.gov.


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.


Primary Concern

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.


Secondary Concern

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.

 


Mountain Weather

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.

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).

Winter snowmachine use open/closed status and riding conditions updates

Riding status is not associated with avalanche danger. An area will be open to motorized use in accordance to the Forest Management Plan when snow coverage is adequate to protect underlying vegetation. Backcountry hazards including avalanche hazard are always present regardless of the open status of motorized use areas.

(Updated: May 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur. This advisory provided by the Chugach National Forest, in partnership with Friends of the Chugach National Forest Avalanche Information Center.


USFS SNOW AND AVALANCHE HOTLINE (907) 754-2369
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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