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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Graham Predeger  
Tuesday, March 29th 2016
Created: Mar 29th 6:28 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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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The Bottom Line

A CONSIDERABLE avalanche danger exists today above 1,000’ where storm snow avalanches 10-20” deep may be easy to trigger by a skier or snowmachiner.  With an increase in elevation, the avalanche problem will transition from a wet snow issue to a wind slab problem in the alpine.  Yesterday’s new snow fell on a fully supportable crust that extends to ridgetops This crust can act as a slick bed surface and any storm snow avalanches initiated today will have the potential to run significant distances.  Daytime warming today will further act to destabilize the storm snow and weaken glide cracks and cornices.

Of course glide cracks continue to plague us in the mid-elevation band and may be covered up by yesterday’s storm.  Keep your head on a swivel and continue to avoid the base of slopes where known glide cracks exist.


Primary Concern

Deep southerly flow yesterday brought .4- 1.1” of water (4-12” of heavy, wet snow above 1,500’) across the eastern Turnagain Arm region with the Girdwood and Portage valleys being favored.  Any new snow fell on a stout melt-freeze crust and the big question today is ‘how well is the new snow bonding to this pre-storm surface’?  It’ll be prudent to ease in to terrain today and seek out small no-consequence test slopes to investigate the storm/ crust interface.  Quick hand pits will also help distinguish how this interface is acting.  With an increase in elevation expect to move from more of a wet snow avalanche problem to a wind slab avalanche problem in the upper elevations.

Heavy, wet snow was plastering to all windward surfaces yesterday including this vehicle in the motorized parking lot  at Turnagain pass.  photo: Ryan Lewthwaite

Wet avalanches: These can be easy to initiate in steep terrain (greater than 35 degrees) and will have the potential to entrain a significant amount of storm snow while gaining mass and momentum.  These can be particularly dangerous when paired with a terrain trap.  Unseasonably warm temperatures today, rain on snow or direct sun will further act to promote wet avalanches failing naturally.

Wind slabs: A brief period of wind toward the end of the storm yesterday likely built tender wind slabs in the alpine.  These may be touchy, particularly on leeward (south and west), wind-loaded slopes.  Expect wind slabs to be in the 16-24” range, again deposited on a stout melt-freeze crust that was found up to ridgetops before the storm.


Secondary Concern

With warming temperatures today and through the week, we could see another spike in glide avalanche activity.  Glide cracks have been avalanching, several per day over the last couple of weeks with at least a couple caught on video HERE and HERE. Avoidance of the crack is best; but easier said than done at this point with glide cracks threatening very popular and well-traveled backcountry routes on both sides of the highway thru Turnagain pass.  Continue to maintain vigilance and limit your exposure to slopes with glide cracks.


Additional Concern

Cornices warrant mention today as well.  We haven’t seen a real active day of widespread cornice failure yet this season.  This just means they continue to grow and creep closer to failure. Warming temperatures this week could act as a catalyst for cornices to fall.  Keep a wide berth both on ridges and when moving below corniced terrain.


Mountain Weather

Moisture-rich southerly flow moved into the region Sunday night bringing storm clouds and consistent rain/ snow showers throughout the day yesterday.  Girdwood and Portage saw the lion-share of moisture with over 2” of water since Sunday evening.  The rain/ snow line was generally between 1,000 – 1,500’ with a bit of wet snow falling as low as a couple hundred feet yesterday morning.  Temperatures at Turnagain Pass averaged in the mid-30’s F at 1,000’ with winds generally light from the northeast before picking up yesterday in the late afternoon.  Gusts late last night hit 64 mph at the Sunburst weather station (3880’) before dying off after midnight.

The moisture looks like it’ll mostly shut off today as the main band of precip moved just east of us overnight.  Temperatures will continue to warm into the mid-30’s at 3,000; some of the warmest temperatures we’ve seen all winter are forecasted this week.  Winds will be light (10-20mph) from the SE with perhaps just a few light rain showers this morning. 

Another wave of moisture moves in late tonight and tomorrow before we see a day of drying on Thursday.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  33  4-6 .4  129 
Summit Lake (1400') 35   1-2 .1  42 
Alyeska Mid (1700') 32   7-12  1.1  119

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 24   ENE 18  64 
Seattle Ridge(2400')  26  SE 28  61 

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: Mar 15, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: Open
Skookum Drainage: OpenSkookum drainage closes to motorized use on April 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: Open
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
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: Open
South Fork Snow River Corridor: Open
Summit Lake: Open

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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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