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Avalanche Advisory

Turnagain Area Avalanche Advisory
Monday, January 22nd 2018 5:49 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

There remains a MODERATE avalanche danger on all aspects above 2,500' for triggering a very large slab avalanche between 3 and 8+' thick. These deep slab avalanches are more likely to be found at the higher elevations, above 3,000'. They are difficult to trigger, but if so could have high consequences. Additionally, loose snow sluffs should be expected on steep slopes and be aware of cornice falls along ridgelines. There is a LOW danger below 2,500' where triggering a slab avalanche is unlikely but sluffs are possible.


 Show the Complete North American Avalanche Danger Scale
2 Moderate Alpine / Above 2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Last night a cold moist air mass brought a several inch refresh to the Girdwood and Portage Valleys (4-6"), yet only an inch or two for Turnagain Pass. Water weight was only in the .25 - .1" range, but most of us will take what we can get to cover the crusts at the lower elevations! With that said, until we see more weather, snow, rain, etc, our avalanche problems on the surface remain on the small side (see below) and our main concern still lies with a much larger, but stubborn avalanche problem.

Deep persistent slab avalanches remain our primary concern, which exist in the high elevation terrain above 3,000'. On these upper elevation slopes, there is a dense hard slab sitting on a variety of weak layers in the mid pack (buried surface hoar) and old November facets near the ground. Triggering a deep slab is becoming more and more difficult, but still possible. The most likely trigger spots are thin areas in the snow cover, often near rocks, or where the slope rolls over. High peaks, that see wind, can also be thinner and more likely to find a deep slab.

Again, here are a few points that keep sending home with our current snowpack set up:

-  We have a 'low probability, high consequence' situation at the upper elevations for deep slab avalanches
-  
Obvious signs of instability are not likely to been seen before a deep slab is triggered (such as whumpfing and cracking)
-  Remote triggering is possible 
-  Last, this issue can simply be avoided by sticking to terrain below 3000’ (which is a good portion of terrain at Turnagain) or choosing low-consequence terrain in the alpine

Photos of old avalanche debris from the Seattle Headwall area. Last week's warm storm initiated very large avalanches on many slopes, yet many still remain intact and did not avalanche. 

  
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Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Ridgetop winds bumped up slightly last night into the 10-15mph range from a generally Easterly direction. This isn't much for wind, but with such loose surface snow existing right now, it could be enough to form shallow wind slabs along ridgelines. Watch for recent wind texturing on the snow surface and feel for stiffer wind packed snow over softer snow or a crust. If you happen to find a fresh wind slab, expect it to be quite touchy.


Additional Concern

Dry Loose

Again, the loose surface snow is quick to sluff and has been running far on steep slopes. Hence, watch your sluff on the steeper slopes. Any additional new snow from overnight will add to the volume of these and could catch a person by surprise. 

Photo of loose surface snow (near surface facets) over a stout crust in the mid-elevations. Another crop of surface hoar (on the top of the snow in photo below) grew last weekend and now sits under the little bit of new snow from last night. 


-


Mountain Weather

Mostly cloudy skies filled the area yesterday with a few snow flurries region wide. Snowfall increased overnight and the Girdwood and Portage Valley areas picked up 4-6" at the mid-upper elevations while Turnagain Pass looks to have seen only around an inch. Ridgetop winds from the East, Northeast bumped up slightly overnight, blowing 10-15mph with gusts into the 20'smph. Temperatures have warmed at the high elevations into the low 20'sF, while valley bottoms remain around 10-15F this morning. 

Today, mostly cloudy skies are expected with a snow flurry or two (little to no accumulation). Ridgetop winds are slated to remain light from an Easterly direction, 5-10mph. Temperatures should warm to the mid-upper 20'sF in valley bottoms and remain near 20F along ridgetops. 

For tonigh night into Tuesday morning there is another chance for a few inches of snow to sea level, possibly up to 6" in favored areas. Winds look to remain light to moderate with this pulse of moisture and temperatures look to remain in the teens to 20'sF. Stay tuned.


*Seattle Ridge anemometer is rimed over and not able to collect wind data.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 11  0.1  54 
Summit Lake (1400') 15 
Alyeska Mid (1700') 12  0.23  47 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 19  NE  21 
Seattle Ridge(2400') 15  *n/a  *n/a  *n/a 

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 06, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: ClosedClosed as of 4/27
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

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
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