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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Sunday, December 14th 2014
Created: Dec 14th 5:57 am
4 High Alpine / Above 2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
0 NO RATING Below Treeline / Below 1,000'
 Show the Complete North American Avalanche Danger Scale
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Special Announcement

The Alaska Avalanche School will be hosting a backcountry weather course, Weather for the Backcountry Traveler, this Wednesday evening. Taught by longtime avalanche professional and Alaska Avalanche School Instructor Eeva Latosuo. This is a great way learn and/or sharpen your weather skills!!


The Bottom Line

The avalanche danger is expected to rise to HIGH later today at elevations above 2,500' where 10-16" of new snow with strong winds are forecast. Natural slab avalanches 1-2' thick, or more, are likely to occur and human triggered avalanches are very likely. In areas receiving less snow the danger will be CONSIDERABLE. Avoiding all avalanche terrain is recommended for today and into tomorrow as this storm system moves through.

At elevations from 1,000' to 2,500' a CONSIDERABLE avalanche danger is expected where avalanches releasing from above have potential to run into this mid-elevation band. At these mid-elevations, we may also see some natural wet avalanches on step slopes where wet snow will accumulate. 

Below 1,000, there is no snow and no danger rating. However, steering clear of the bottom of avalanche path runout zones where debris from above could funnel into this snow free zone is advised. For example, avoiding hiking along trails in the Portage Valley.

Today looks to be a good day for Christmas shopping.

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The next advisory will be Tuesday Dec16th at 7am.

Avalanche Outlook for Monday: The avalanche danger is expected to remain HIGH above treeline in areas seeing over a foot of snow today and CONSIDERABLE at treeline. Sunday night through Monday evening an additional 10-16" of snow is forecast to fall above 1,500 with ~1.5" of rain below 1,500'.


Primary Concern

A warm and very intense storm is arriving as we speak. The rain/snow line should rise to 2,000' and 10-16" of snow is forecast above 2,500'. Associated with the new snow will be very strong Easterly ridgetop winds. This is a classic storm snow avalanche problem. With wind likely to affect most locations above 2,500', naturally occurring wind slab avalanches are expected on many leeward slopes. These are expected to run into the 2,000' elevation zone, where it may be raining, and possibly further.

Not only is a foot or more of new snow falling in 12 hours, accompanied by strong winds, a concern in itself, it is falling on a very weak pre-existing surface. Widespread surface hoar up to the ridgetops - 2cm (3/4") in size, which is significant - was just starting to be covered up intact and upright yesterday. Hence, bonding between the new snow and old snow will be poor with this persistent weak layer sandwiched in between. As snow piles up and becomes cohesive with the warm temperatures, slabs will have potential for wide propagation.

Slab depths for today's expected new snow will be in the 1-2' range. These are not exceedingly thick slabs for a HIGH danger day, but the expected rapid loading on a weak layer of surface hoar should produce widespread avalanche activity with dense debris. Steering clear of avalanche terrain while it continues to snow and blow is recommended.


Secondary Concern

Rain on an old battered and frozen snowpack is expected from ~2,000' and below. Above this, around 2,500', 6-8" of wet snow is likely to fall on a stout and well developed crust. Naturally occurring wet loose avalanches composed of the new wet snow are likely to run on steep slopes. Areas that are in this zone are the East face of Seattle Ridge and Magnum's West face.


Mountain Weather

Yesterday, skies were mostly cloudy with light snow beginning to fall in the early afternoon as the leading edge of today's low pressure system pushed in. The rain/snow line rose to 500' by the evening. Don't forget about the table below for additional past 24-hour weather details!

Overnight we have seen ~.3-.5 of rain below ~1000 in the Girdwood Valley and Portage area with 4" of wet snow at the Center Ridge (Turnagain Pass) SNOTEL site at 1880'. Ridgetop Easterly winds are on the rise from the teens to the 30'smph with gusts to the 50's. Temperatures are steadily climbing (unfortunately) with 1,000' temperatures in the mid 30'sF.

Today, we will see temperatures rise another few degrees F with the rain/snow line creeping to 2,000'. Between 1 and 1.5" of water equivalent is expected by this evening at Turnagain Pass with 10-15" of snow at the above treeline elevations. Ridgetop Easterly winds are forecast to be in the 30-40mph range with stronger gusts.

Monday, precipitation, Easterly wind and even temperature should decrease slightly. Models are showing 1 - 1.5" of rain below 1,500' and another 10-16" of snow above.

A series of low pressure systems will continue to move through the Northern Gulf with additional cooler temperatures and additional snow (hopefully to sea level). Stay tuned.

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 31  0.4  22 
Summit Lake (1400') 28  4
Alyeska Mid (1700') 32  0.6  15 

 

RIDGETOP 24-hour data (6am - 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 25   E 21  54 
Seattle Ridge(2400') 27   SE 15  31 

 

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: Apr 28, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: ClosedSKOOKUM DRAINAGE CLOSED TO MOTORIZED USE ON APRIL 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: OpenOpen thru May 14th.
Twentymile: Closed
Seward District
Carter Lake: OpenClosed May 1.
Lost Lake Trail: OpenClosed May 1.
Primrose Trail: OpenClosed May 1.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: OpenClosed May 1.
South Fork Snow River Corridor: OpenClosed May 1.
Summit Lake: OpenClosed May 1.

Subscribe to the Turnagain Area Avalanche Advisory:

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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