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Avalanche Advisory

Turnagain Area Avalanche Advisory
Sunday, January 14th 2018 5:43 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger is CONSIDERABLE on all slopes above 1,000'. Triggering a 2-3+' large slab avalanche, composed of the new snow, is likely above 1,500'. Wet slab avalanches near and below 1,500' are possible. Naturally occurring avalanches are also possible. Additionally, avalanches could break in deeper layers of the snowpack, causing a much larger slide. Below 1,000' the avalanche danger is MODERATE for wet loose avalanches. 

*Today is a day to let the mountains adjust to the several feet of recent new snow. Cautious route-finding and conservative decision-making will be essential. 


 Show the Complete North American Avalanche Danger Scale
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.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

A break in the weather has finally moved in after three days of rain, snow and wind. The rain/snow line rose to 1,500' in places yesterday, and possibly higher, yet several feet of new snow is now in the mountains above 1,500'. During the past 24 hours between 1-2' of new snow fell in the region. Favored locations were Portage Valley, Girdwood and the North end of Turnagain Pass. 

STORM TOTALS near 2,000' above the rain - Thursday morning through 6am Sunday morning:

Turnagain Pass     20-30"  (2.6" of snow water equivalent)
Girdwood Valley    25-35"  (3.2" of snow water equivalent)
Summit Lake         10-15"  (1.0" of snow water equivalent)

Avalanche activity was prevalent in the Tincan Trees yesterday due to heavy snowfall creating a 'rapid loading' event. All avalanches were failing under the total storm snow, at the new/old snow surface. The old snow surface is composed of small buried surface hoar (3-7mm) and near surface facets. These are persistent weak layers that don't bond quickly. Hence, we can expect the storm snow to fail in these layers again today. With the storm past, natural avalanche activity will be decreasing but human triggered avalanches will remain likely. If you are headed out - keep these points in mind:

1-  Slabs triggered will be deep (2-3+ feet) - these are dangerous and unmanageable avalanches
2-  Avalanches could run further than expected
3-  Remote triggering an avalanche from below, or near a slope is possible
4-  Due to the depth of the storm snow, no signs of instability may be present before someone triggers a slab

*Giving the snowpack time to heal from these storms is key. Sticking to low angle terrain with nothing steeper above is recommended. Remember, it's the first 2 days after a storm where most avalanche fatalities occur. Although there is nice powder at the upper elevations that can lure us, now is not the time to be sampling it.
 

Stom slab avalanches in the Tincan Trees yesterday. The slab on the left was believed to have been natural while the slab on the right was remotely triggered by a group ascending. Recent avalanches, Bulls Eye clues the snowpack is unstable.

 

Another storm slab avalanche triggered by a skier in the Tincan Trees, note the size of the slab (~2,5' thick). Big thanks to the folks who sent this photo in to us.


-

 


Avalanche Problem 2

Wet Slab

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Rain fell on snow yesterday up to 1,500' and today, light rain is expected to fall up to 2,200'. With these warm temperatures persisting, wet slab and wet loose avalanches remain possible. There have been some breaks in cloud cover overnight, which has likely helped to start freezing the snow surface at these lower elevations. However, clouds and light rain should move back in today softening any crusts that may have formed. Keep in mind that steep slopes with a wet and saturated snowpack are likely to slide. Even a small slope could have high consequences if heavy wet debris is able to pile up on a person. 


Additional Concern

Deep Persistent Slabs

Weak layers within the snowpack have the potential to re-activate with the added load of this week's new snow (2-3+" of water weight). Additionally, avalanches in the storm snow, discussed above, could step down to these deeper layers and produce a very large avalanche depending on the size of the slope. In short, a layer of buried surface hoar from the New Year’s holiday sits roughly 3-6' deep at this point and is a concern at elevations above 2,000'. Basal facets, near the ground, remain a concern at elevations above 3,000'. 


Mountain Weather

Yesterday's storm peaked around noon and brought 1-2" of rain to 1,500' in most locations with moist snow above this. The greater amounts of precipitation seen were in the Portage Valley area. Snowfall in the upper elevations varied from 1-2 feet; Girdwood Valley and the North end of Turnagain Pass saw near 2' of snow while the South end of the Pass and Summit Lake saw 12-15" of new snow. Ridgetop winds were strong from the East, averaging 30-60mph with gusts to 99mph. Temperatures were warm, around 36F at 1,000' and the mid to upper 20'sF along ridgetops. 

Currently, the fire hose of moisture has shifted to our East  and precipitation has decreased significantly. Today we can expect light precipitation with 1-2" of snow above 2,200' and ~.1" of rain below this. Skies could clear slightly at times before light precipitation moves back in for this evening along with cooler temperatures. We could see another 2-5" inches of snow above 1,000' and .3" of rain below this. Ridgetop winds will remain Easterly and expected to be in the 15-25mph range.

For tomorrow, Martin Luther King Day, we can expect partly to mostly cloudy skies with light snow flurries. Temperatures should remain cool enough for snow to fall to 1,000'. The next system looks to move in on Tuesday and again is a warm one. 

*Seattle Ridge anemometer is covered in rime from this storm and not functioning

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 32  11  1.3  66 
Summit Lake (1400') 33  rain  0.9  15 
Alyeska Mid (1700') 33  1.7  48 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 25  NE  39  99 
Seattle Ridge(2400') 28  *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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